View Full Version : Is it worth changing gears for better MPG's???
Time too time the topic of switching rear end ratio's comes up to save fuel and there for $$. Here is a little though and calculation I came up with on this topic. The conclusions will vary based on your cost and if you have 2 wheel drive vs 4 wheel drive. The calculations are based on 4x4.
If you pickup 2 mpg going from a 4.10 to a 3.73 ratio which assume you average 16 mpg and then would average 18 mpg. 16 MPG would take 62.5 gallons to go 1,000 miles 18 MPG would take 55.5 gallons per 1,000 miles. That is a savings of 7 gals per 1K miles or $21 per 1k at $3 per gallon. So if it cost $1800 to swap gears ($800-900 per axle) $1800/$21=85.7k miles or 85,700 miles to break even. Now unless you tow heavy and a lot say over 7,000 lbs I would consider going up too 3.42 ratio the cost would be about the same and if you pick up an extra 1 MPG that would mean it would take 52.6 gallons per 1K miles or 9.9 gallons less or a saving of $29.70/1k miles. $1800/$29.7=60.6k miles or 60,600 miles to break even.
So anything over 61,000 miles and your ahead of the game. The key is HOW LONG do you plan on keep your truck or really how many miles do you plan on keeping your truck??? If you keep the truck for about another 100,000 miles you would save ~ $1200 in fuel cost @ $3/gal and 3 mpg increase.
Gear changing was something More Power talked about more in the early days at The Page.
I did this calculations back when I had about 30,000 miles on my truck and did the swap at 38,000 miles and figured it at $1.35 per gallon for Diesel. It worked out that I need to keep the truck at least 60,000 miles to break even. MY goals/was to drive the truck too at least 300,000 miles. With about 110,000 miles past break even on my truck and with fuel cost well above the $1.35 I used I am way ahead.
So. I believe it is feasible to change axel ratio's out and save enough to pay for it self PROVIDED you drive the truck enough.
So if you only keep the truck for 20 or 30,000 miles after changing gears your only wasting money and helping the next owner.
A couple other thoughts about changing rear end gearing, More Power said in another thread when he did it on his old K-5 Blazer it made the truck much more pleasant too drive.I found this true also, lower engine and drive train noise. Jim in the early days talked about extending engine life by going to 3.42's from 4.10's by an estimated 100,000 miles and maybe 50-75,000 miles going from 3.73's (my old ratio) too 3.42's. At the time with a New 6.5 this was important too me. Maybe it's not as important to folks who buy a now well used 6.5TD as it was then. I do think there maybe few folks like myself who buya truck for a long time and want to keep their long term cost and headaches to a minium.
In conclusion I think changing gears is a good option for some but not all 6.5TD owners. If your considering this consider your towing profile, type of usage, and expected ownership time frame.
john8662
06-19-2006, 13:15
I just wanna go faster!
Didn't like the 75mph interstate traffic with me driving 70 and getting looks from other drivers like that was the fastest my rig could go. It could go faster but at the cost of fuel economy and my ears.
6.5 4.10 gears..
Planning on the 4.10 to 3.42 swap, doesn't make sense to go 3.73 since I don't pull too often and too heavy anyways (just the weight of another vehicle occasionally).
This way, all RJ has to do is follow the black cloud ;)
J
More Power
06-19-2006, 13:47
I agree with John & Marty... Switching gears from 4.10 to 3.73 might not be worth the investment. If your use of the truck is primarily non-towing, then 3.42 is your best choice.
I encourage people to look at how they use their truck to determine whether they should invest in a gear swap. If you use your truck to tow heavy, then stick with 4.10's. You need the gear reduction. Otherwise, you'll notice a big improvement in driving pleasure as well as a bump in fuel economy when going from 4.10's to 3.42's for a non-towing or light towing use.
The cost of a gear swap is highly variable - depending on whether you can do the work or if you hire the work out. The parts aren't really all that expensive, but getting the gears set up correctly is vital for a long and noise-free gearset life.
To get an idea of what the driving experience will be like when going from 4.10's to 3.42's, take your truck up to 65 mph out on the highway, then put the trans in neutral with the engine idling. After switiching to 3.42's and while running in OD, the engine noise almost completely goes away.... :)
Back in the mid 90's I added an OD auto (it had a non-OD auto) and a Banks turbo to a 6.2 GMC K1500. If I were forced to choose just one of these two upgrades, I would choose the OD auto - just for how nice it made the truck to drive on the highway - regardless of how it affected mpg (although it added about 5 mpg). The truck already had 3.42 gears.
Jim
DA BIG ONE
06-19-2006, 15:21
It would be 3.73 for me the next time around because of the autotrac. What would be nicer is a stand alone tranny controller so I could stay w/3.42's.
moondoggie
06-19-2006, 19:20
[font=times][size=+]Good Day!
I picked up ~ 2 mpg going from ~ 3.80 effective ratio (4.10 gears w/ 8% oversized tires) to 3.08 effective ratio (4% oversize tires + Gear Vendors Aux. OD).
To figure out when a modification will pay for itself, put this in your spreadsheet program (do NOT input the quotes
How about the 5sp manual trannys. They about the same ratio as the automatics?
arveetek
06-20-2006, 09:58
Good info!
What's funny is that my 4.10 geared powerhouse 6.2L turbo truck gets about the same mileage as my 3.42 geared 6.5L family car...around 16-17 mpg.
However, the Tahoe will cruise at 75 mph all day long without breaking a sweat and without much noise. The truck struggles to get to that speed, and the noise is quite annoying. Both vehicles have overdrive transmissions.
The truck is designed to tow trailers, and does a marvelous job at it. But it sure doesn't like long-distance interstate driving.
Casey
How about the 5sp manual trannys. They about the same ratio as the automatics?
IIRC, the 4L80E overdrive ratio is 0.74:1 and the NV4500 is 0.71:1
winemaker
06-20-2006, 21:01
I just got my truck, 1996 2500 6.5td, 5spd, xcab 4x4, at the end of May. The guy I bought the truck from didn't know the diff. ratio. How would I find out what mine is? I pressume it's stock because everything else was. My buddy thinks they're 3.73, but I don't have a clue. The only hint I have is that, unless I have a load on, and am stopped on a hill, I don't use 1st gear. Cheers! Brett
I thought the OD ratio's for the auto vs manual were opposite of what John wrote, ie the auto was a .71 vs tha manual at .74. Where the auto lose's, is the first gear effective ratio. The manual depending upon yr, is 5.64 for later NV4500's or 6.34 for the early IIRC pre 94 NV4500's or ANY of the dodge tranny 4500's. Where as the auto first gear effective ratio is about 4-1. A 1.64-1 difference, quite abit when it comes to take off! You can have 3.08's with a manual, and still have better take off than a auto with 4.10s, and if you can drive in OD, what should be great MPG's!
If you tow, be carefull about changeing out gears, you may lose all you take off ability if you go too tall.
what is lowest ring and pinion you can get for a 4x4? The lowest i have seen is 3.42.
TurboDiverArt
06-27-2006, 18:05
It would be 3.73 for me the next time around because of the autotrac. What would be nicer is a stand alone tranny controller so I could stay w/3.42's.
You and I have similar trucks. Why is the auto track a problem with 3.42
DA BIG ONE
06-28-2006, 02:59
[QUOTE=TurboDiverArt]You and I have similar trucks. Why is the auto track a problem with 3.42
TurboDiverArt
06-28-2006, 03:08
I'm thinking as 4x4 2500 burb is raised catching more air the 3.42 is ok w/stock, even slightly larger sized tires, after this I think the drivetrain gets loaded "height/weight/speed" and defeats any would be gains milage wise. However, the tires I used were 285/75/16 GoodYear MT/R's so that may be the problem, now using 285 SilentArmor which is more highway friendly, so flip a coin now. The forged alcoa's 16" x 7"w/285 silentarmor weigh about the same as the factory 16" x 6.5" riveted steel wheel w/stock 245 tires.
I'm thinking, stay w/the gears you have now and go for larger diameter tires that would equate to 3.42 +- & don't use a too aggressive tread pattern. You'll be looking at od/lockup @ 60mph +-.
As for towing? With my mods, I don't see much of a loss except from a stop but I don't really tow too much.
That's sort of my feeling. I really don't stomp on it much from a stand still so I don't expect to see much difference. For towing, based on the last rendezvous pull-off, the stock pickup with 3.42 gears pulled the heavy tow trailer in about the same times as a stock truck with lower stock gears so I don't think towing is too much effected.
When you have the 3.42's and the VSS hacked so speed is corrected, is the OD-converter lockup speed raised from 48 to 60 MPH? I guess I just assumed the lockup parameters would stay the same if the VSS were properly set.
Art.
DA BIG ONE
06-28-2006, 03:30
That's sort of my feeling. I really don't stomp on it much from a stand still so I don't expect to see much difference. For towing, based on the last rendezvous pull-off, the stock pickup with 3.42 gears pulled the heavy tow trailer in about the same times as a stock truck with lower stock gears so I don't think towing is too much effected.
When you have the 3.42's and the VSS hacked so speed is corrected, is the OD-converter lockup speed raised from 48 to 60 MPH? I guess I just assumed the lockup parameters would stay the same if the VSS were properly set.
Art.
Yes, hacking the VSSB only gives od/lockup @ 60+-.
I have hacked the signal to the vssb from the VSS and the shift points for the 4.10 gearset remained even though gears are now 3.42. However, I get some banging of gears on occasion, I'm thinking this is because I have a shift kit (transgo towing/off road), and the PCM is upgraded with shift mods too. It shifts fast when driven normal, holds gears a little longer when I stomp it.
Looking now at hacking vssb for 3.42 gearset, then modifing the signal from vss for tire changes, this will keep the od/lockup at 55 mph+-.
Keep in mind I have a full tilt 4L80e w/all updates so it may take more of a beating than say a tranny w/shift kit. So, proceed w/caution when hacking just the signal from vss to vssb.
That's sort of my feeling. I really don't stomp on it much from a stand still so I don't expect to see much difference. For towing, based on the last rendezvous pull-off, the stock pickup with 3.42 gears pulled the heavy tow trailer in about the same times as a stock truck with lower stock gears so I don't think towing is too much effected.
Art.
Art;
That was my truck at the Pull Off your talking about. And I tow a lot about 5,000 lbs. I have towed bumper pull Travel Trailers from Yuma Arizona to Great FAlls Montana right up through the middle of several Mountain ranges. The largest TT I have pulled was 27 foot and my truck handled it fine and that was before the Heath MaxiTorq EPROM. This is always in January or February how ever. I have had the 3.42 gearing for about 170,000 miles and I feel that with my set up I can two 7-8,000 lbs with no worries. If I was towing more than that on a regular basis I would have the 3.73 gears put back in. Also it is not just weight but Aerodynamic drag has big affect. The last TT I brought back was a "18" foot but did include the hitch so it was about a 22 foot if you include the hitch to bumper. The weight wasn't bad empty like 4,700 lbs but I got the worse fuel economy pulling this trailer than any I have pulled. I pulled the passes fine but the thing was very Areodynamic dirty. Frontal area like a 2 4x8 sheets of plywood, high clearance axels, A/C and storage locker on the roof and TV anenta, and awning, crank down jacks hanging dwon on all the corners. This TTweights about the same as mine but mine sits lower too the ground, sloped front end, not much on the roof no A/C storage locker or jacks hanging down. I get 12 to 13 MPG towing it were the Dirty trailer I averaged 10 MPG. The difference between 10 & 12 MPG 1s 20% and the 10 MPG TT takes 17 gallons more fuel on a 1,000 trip. Thats a $50 bill at $3 per gallon. So to wrap this up I find the 3.42's do a good job towing in the lighter and middle weights for towing. I don't mind towing heavier once in awhile.
DA BIG ONE
06-28-2006, 13:25
ART, Just a tire size change to 285/75/16 and your 3.73's will give you a final of 3.42+-
TurboDiverArt
06-29-2006, 03:47
ART, Just a tire size change to 285/75/16 and your 3.73's will give you a final of 3.42+-
I wasn't intending on making a big change in tread width. I think increasing the cross section of the tire from 9.6" to 11.2" will probably have a pretty big adverse effect on MPG. Additionally I think it'll be much louder.
If I kept the stock height I was planning on using a 245/70-17 tire.
If I went up I was thinking of using a 255/75-17. I think this brings me pretty close. Might not be down to 3.42's but definitely at least 3.55's. Increases the height of the tire from 30.46
DA BIG ONE
06-29-2006, 04:46
I wasn't intending on making a big change in tread width. I think increasing the cross section of the tire from 9.6" to 11.2" will probably have a pretty big adverse effect on MPG. Additionally I think it'll be much louder.
If I kept the stock height I was planning on using a 245/70-17 tire.
If I went up I was thinking of using a 255/75-17. I think this brings me pretty close. Might not be down to 3.42's but definitely at least 3.55's. Increases the height of the tire from 30.46” to 32.06” or 1.6”. I think the ideal height change is probably closer to 2” to get it real correct. Don’t know how precise you can be with correcting the speed sensor.
Not having the converter lock up until 60 MPH is a little bit of a concern for me though. That means that on most state routes around here where the speed limit is 50 MPH I probably won't get the converter to lock up as I usually don't go more than 10 MPH over the speed limit as there are just too many police waiting to give me a ticket. It’s nice that at 50 MPH the converter will lockup. Did know that the 1500 Suburban’s with stock 3.42’s locked up at 60. Does this mean that a truck with 4.10's locks up before 48 mph?
Can someone point me to the article regarding hacking the VSS/VSSB?
In your post above you mention modifying the signal from the VSS (at trans?) as well as modifying the VSSB? I guess I didn’t think that there were two things in play here that could be modified. My thought was to hack the sensor signal (resistor or something) under the dash. Thought doing this would correct for the gearing so that based on output shaft speed the gauges and computer would read speed correctly. Again, I didn't know that this had an effect on how the PCM instructed the transmission to lockup. Does it also have an effect on shift point? I think I'm confused on how this works. My assumption was that you were correcting the speed but the computer still functioned the lockup at the same speed regardless of gearing, 48MPH for 3.42’s through 4.10’s.
Art.
Art, I'm thinking closer to 45mph for od/lockup w/4.10's. I also think using cruse control locks converter too.
Tire width does effect milage, but tread pattern plays bigger role the MT/R's I used made mpg suffer, the SilentArmor is more road friendly and quieter so not as bad.
Your vss is on the t-case along w/2 other speed sensors, 1 for the front drive shaft, 1 for the rear driveshaft. I just discovered the "vss" hack works a little while ago.
Hacking the speed signal from the vss to the vssb will correct the speedo only and leave the 3.73 shift/lockpoints you have now.
Hacking the vssb you modify speedo, shift/lockup to higher mph setting, abs, cruse control. TheDieselPage sells the book showing the hack of VSSB.
I used a commercial VSS re-calibrator to modify vss signal only.
Getting accurate on speedo calibration comes w/hack either way, especially if you measure tire diameter and use this measurement in re-cal.
LanduytG
06-29-2006, 04:49
Who's a good source now days for the gear sets?
Greg
moondoggie
06-29-2006, 07:36
Good Day!
"I used a commercial VSS re-calibrator to modify vss signal only." Could you be more specific? Jim doesn't mind at all if we mention product names, as long as we're not hawking them.
Hacking the VSS signal looks like it would NOT be a resistor or pot situation - from a quick glance, that signal is a frequency that would have to be multiplied or divided to hack (clarification please).
Blessings!
(signature in previous post)
TurboDiverArt
06-29-2006, 08:48
Art, I'm thinking closer to 45mph for od/lockup w/4.10's. I also think using cruse control locks converter too.
Tire width does effect milage, but tread pattern plays bigger role the MT/R's I used made mpg suffer, the SilentArmor is more road friendly and quieter so not as bad.
Your vss is on the t-case along w/2 other speed sensors, 1 for the front drive shaft, 1 for the rear driveshaft. I just discovered the "vss" hack works a little while ago.
Hacking the speed signal from the vss to the vssb will correct the speedo only and leave the 3.73 shift/lockpoints you have now.
Hacking the vssb you modify speedo, shift/lockup to higher mph setting, abs, cruse control. TheDieselPage sells the book showing the hack of VSSB.
I used a commercial VSS re-calibrator to modify vss signal only.
Getting accurate on speedo calibration comes w/hack either way, especially if you measure tire diameter and use this measurement in re-cal.
That
TurboDiverArt
06-29-2006, 09:03
Hacking the speed signal from the vss to the vssb will correct the speedo only and leave the 3.73 shift/lockpoints you have now.
Hacking the vssb you modify speedo, shift/lockup to higher mph setting, abs, cruse control. TheDieselPage sells the book showing the hack of VSSB.
OK, reading into your post a little more.
Assuming that from a calibration standpoint the 4.10 VSSB setting does not affect mileage in itself or general health/management of the engine and drive train. Would it make sense, or is it even possible, to set the VSSB to 4.10
DA BIG ONE
06-29-2006, 09:25
Good Day!
"I used a commercial VSS re-calibrator to modify vss signal only." Could you be more specific? Jim doesn't mind at all if we mention product names, as long as we're not hawking them.
Hacking the VSS signal looks like it would NOT be a resistor or pot situation - from a quick glance, that signal is a frequency that would have to be multiplied or divided to hack (clarification please).
Blessings!
(signature in previous post)
Ok, It is called and "electronic ratio adapter" (ERA) from ABBOTT ENTERPRISES, INC. Just use your divide ratio between changes match it the switch settings (micro-rockers) and your goos to go.
www.abbott-tach.com or www.atrol.com
TurboDiverArt
06-29-2006, 12:51
Ok, It is called and "electronic ratio adapter" (ERA) from ABBOTT ENTERPRISES, INC. Just use your divide ratio between changes match it the switch settings (micro-rockers) and your goos to go.
www.abbott-tach.com or www.atrol.com
I assume you put this in series? Meaning you cut the signal wire going from the VSS to the VSSB and put the ERA in the middle? That way the VSSB knows the actual speed as modified by the ERA but thinks the gearing is still stock?
Art.
moondoggie
06-29-2006, 16:28
Good Day!
Thanks!
Blessings!
(signature in previous post)
DA BIG ONE
06-29-2006, 17:04
I assume you put this in series? Meaning you cut the signal wire going from the VSS to the VSSB and put the ERA in the middle? That way the VSSB knows the actual speed as modified by the ERA but thinks the gearing is still stock?
Art.
Yes, that's it.
As for engine management on the 1999 6.5 w/NP246 the vss output signal @ pin C-11 from vssb does not connect to pin F-13 (speed signal) @ pcm.
DA BIG ONE
06-29-2006, 17:42
JET makes a re-calibrator SCU-2000 that hacks vss only, in a recent e-mail to them I asked if it will function w/NP246, they replied yes.
Their unit plugs into harness at t-case then requires modual to be installed into vehicle.
TurboDiverArt
06-30-2006, 05:44
Yes, that's it.
As for engine management on the 1999 6.5 w/NP246 the vss output signal @ pin C-11 from vssb does not connect to pin F-13 (speed signal) @ pcm.
Just for my own clarification. There are two computers at play, right? The PCM that controls the drive train and the ECU that controls the engine? If correct, any idea which each uses the speed signal for and why? What's the VSSB feeding then if not the PCM? Only the gauges?
Sorry for so many questions but I think it's an interesting topic and conversation.
Art.
ronniejoe
06-30-2006, 06:05
The PCM or Powertrain Control Module controls both the engine and the transmission (and senses engagement of the front differential). Therefore, it controls the entire powertrain of the vehicle. It's one box. There is no ECU or ECM separate from the PCM.
TurboDiverArt
06-30-2006, 07:35
The PCM or Powertrain Control Module controls both the engine and the transmission (and senses engagement of the front differential). Therefore, it controls the entire powertrain of the vehicle. It's one box. There is no ECU or ECM separate from the PCM.
I didn't know that, thanks!! For some reason I thought there were two computers in play. So, when you upgrade to a Heath or other computer, it's the PCM you are upgrading?
This begs the question, if the PCM is not getting speed from the VSSB as stated above, where does it get it from? I'd think it would care for management of the transmission, cruise, etc.
Art.
ronniejoe
06-30-2006, 08:41
Actually, it does get it from the VSSB. I'm not real sure I understand everything stated earlier in this thread.
DA BIG ONE
06-30-2006, 09:01
Actually, it does get it from the VSSB. I'm not real sure I understand everything stated earlier in this thread.
Hello RJ, I'm by not means an expert, but this is what I've found when hacking VSSB. When switching gears, or changing tire sizes hacking vssb to correct speedo also changes shift/lockup points by the same %. However, if the vssb is not hacked and only the vss is then speedo is corrected but the shift points/lockup all stay at the points they were before the gear/tire change.
DA BIG ONE
06-30-2006, 09:12
My burb came w/4.10's when I changed out the gears to 3.42's I hacked the vssb the speedo then the shift/lockup points all changed the same % of the change ratio w/od/lockup at 60+- mph.
I rehacked the vssb to the original 4.10 setting "even though I still have the 3.42'2 and then hacked the vss to correct the speedo, the result was quicker shift/lockup points w/od/lockup at 45+- mph.
The vssb on the 1999 diesel burb I have does not include the C-11 (VSS) pin hookup connected to the F-13 pin @ PCM, not sure if this is because of the AutoTrac, or?
So, If one has a 3.73 gearset then hacks the vssb to think there are 4.10's then hacks vss to correct speedo, the shift/lockup points will be closer together, go the other way and the shift/lockup points will be farther apart.
DA BIG ONE
06-30-2006, 09:24
I didn't know that, thanks!! For some reason I thought there were two computers in play. So, when you upgrade to a Heath or other computer, it's the PCM you are upgrading?
This begs the question, if the PCM is not getting speed from the VSSB as stated above, where does it get it from? I'd think it would care for management of the transmission, cruise, etc.
Art.
@ vss 821 purple/white line "high resistance vss output" to pin C-12 vss input @vssb
@vss 822 lt green/blk line "vss output" to pin C-7 vss input @ vssb
C-8 @ vssb 451 blk/wht body ground
C-9 @ vssb 441 BRN 10 amp power ign on
C-10 @ vssb 690 wht to antilock ABS
C-11 @ vssb output blank but drawings have it going to F-13 of PCM
C-13 @vssb transmission output 437 bwn to F-12 @ PCM transmission output speed (NOTE: I don't know if this is an in or out signal at vssb) surely others may know.
C-14 @ vssb output 817 grn/wht to cruse control
C-15 @ vssb 389 dk grn to speedo
moondoggie
06-30-2006, 09:26
Good Day!
Owning two 95 6.5's has been handy. The pickup has 4.10 gears, the Sub 3.42. I noticed the higher shift points on the Sub right away. I'm quite sure the shift points are controlled by shaft rpms (& footfeed position etc), NOT vehicle speed.
As fuel economy is my only hobby, this is of interest. I'd like lower shift points, & even more, an earlier TC lockup in the Sub, more like how the pickup shifts.
This thread has been very profitable for me. It never occurred to me that there was a way to hack the VSS signal - the links provided earlier in this topic show this is readily available. Some day I'd REALLY like to do this to our Sub.
I'll plagiarize a local radio show - you learn more here by accident than anywhere else on purpose. Thanks again, folks, for helping me keep my junk running, & running the way I like.
Blessings!
(signature in previous post)
.... When switching gears, or changing tire sizes hacking vssb to correct speedo also changes shift/lockup points by the same %. However, if the vssb is not hacked and only the vss is then speedo is corrected but the shift points/lockup all stay at the points they were before the gear/tire change.
I thought we flogged this one beyond death a while back. This may be a semantic argument, but...
Shift points and lockup are controlled relative to (as they should be) the torque curve of the engine as it relates to engine RPM, NOT by road speed. When you change the axle ratio, the shift points do NOT change (relative to engine speed). Hacking the VSSB has no effect one way or the other, except to make the speedo reflect the actual road speeds. What you have accomplished with the double fake is to move the shift points lower on the torque curve, thus maintaining shift points at the same road speed as before but at lower engine speeds. Maybe good for unloaded economy, but wrong for everything else.
Had you purchased the vehicle with the 3.42 gears, the shift points would not be where you have them now.
It is interesting to note that otherwise identical LD and HD chips differ in TCC lockup speed. the HD chip is set about 5 mph higher to allow torque multiplication farther into the power band.
That's my story and I'm stickin' to it...
TurboDiverArt
06-30-2006, 10:46
I thought we flogged this one beyond death a while back. This may be a semantic argument, but...
Shift points and lockup are controlled relative to (as they should be) the torque curve of the engine as it relates to engine RPM, NOT by road speed. When you change the axle ratio, the shift points do NOT change (relative to engine speed). Hacking the VSSB has no effect one way or the other, except to make the speedo reflect the actual road speeds. What you have accomplished with the double fake is to move the shift points lower on the torque curve, thus maintaining shift points at the same road speed as before but at lower engine speeds. Maybe good for unloaded economy, but wrong for everything else.
Had you purchased the vehicle with the 3.42 gears, the shift points would not be where you have them now.
It is interesting to note that otherwise identical LD and HD chips differ in TCC lockup speed. the HD chip is set about 5 mph higher to allow torque multiplication farther into the power band.
That's my story and I'm stickin' to it...
If I'm understanding things correctly, I "think" we are all talking the same thing but using different or maybe slightly incorrect semantics. You are definitely correct that the shift point is load and TPS based and not strictly RPM based.
One area I think I'm going to disagree with you on is that the stock shift points are where you want them and that lowering them somewhat is not what you want to do. Yes you hold torque multiplication longer by delaying the shift point higher in the RPM range but torque multiplication is power in multiplied by the gear ratio. So, making the shift point above the max output on the torque curve means less power into the torque multiplication so less power out. Now, you do have to shift higher than the max torque otherwise the bottom of the shift will be below the torque curve and the truck makes no power after the shift. I don
moondoggie
06-30-2006, 12:06
Good Day!
"...(as they should be)..." I might drive my truck different than you do, so maybe what you think is best isn't best for me. I'd prefer to help you get your truck where you want it (unlikely - you've forgotten more than I'll probably ever know about these things) & you help me get mine where I want it. ;) If what I want to do with my truck might hurt it, it'd be nice if you'd let me know, however - I'd certainly do the same for you.
"Maybe good for unloaded economy, but wrong for everything else." Well, maybe that's at least one of the things I'd like to try eh? :)
"I thought we flogged this one beyond death a while back." Is it just possible one of us hit JohnC's hot button? :eek: Please take no offense - none intended. Like I said, I need you folks to help me keep my junk running, especially experts like JohnC. ;)
Blessings!
(signature in previous post)
ronniejoe
06-30-2006, 12:41
[quote=TurboDiverArt]As the truck increases past about 2800 the truck seems to make less and less power. It's like someone has engaged cruise control. I hit 3400 or so, switch gears, drop below 2800 and she starts pulling again, get past 2800 and the acceleration rate drops. At least by the "seat-o-pants" meter, if I stomp on it, let it get to about 2800-3000 RPM's, let off the throttle a little so it shifts and then increase the throttle (making sure it doesn
DA BIG ONE
06-30-2006, 12:44
[QUOTE=TurboDiverArt]If I'm understanding things correctly, I "think" we are all talking the same thing but using different or maybe slightly incorrect semantics. You are definitely correct that the shift point is load and TPS based and not strictly RPM based.
One area I think I'm going to disagree with you on is that the stock shift points are where you want them and that lowering them somewhat is not what you want to do. Yes you hold torque multiplication longer by delaying the shift point higher in the RPM range but torque multiplication is power in multiplied by the gear ratio. So, making the shift point above the max output on the torque curve means less power into the torque multiplication so less power out. Now, you do have to shift higher than the max torque otherwise the bottom of the shift will be below the torque curve and the truck makes no power after the shift. I don
ronniejoe
06-30-2006, 12:59
The shift points should actually be near the engine's power peak because power is the rate at which work is being done. You want the work to be done at as fast a rate as possible to get down the road as quickly as possible.
DA BIG ONE
06-30-2006, 13:23
The shift points should actually be near the engine's power peak because power is the rate at which work is being done. You want the work to be done at as fast a rate as possible to get down the road as quickly as possible.
Hello RJ, When you mention power peak, is this torque, or hp, or somewhere in between? In my case peak torque is at 2,200 rpm's, peak hp is at 3,500 rpm's, I'm thinking peak torque, right, or?
TurboDiverArt
06-30-2006, 15:02
Yes I believe you are all correct in that you want the shift at peak torque, in fact you want the engine to always operate at this point. But.... after the shift you don't want to be out of the power range either. If you shift at 2200 RPM
ronniejoe
06-30-2006, 15:56
I am talking about power as measured in HP. The engine is most efficient at its torque peak, but gets the work done more quickly at its power peak.
Now in the case of these engines in stock form, the real optimum point is around 2700 - 2800 rpm where the rate of increase of power (second derivative...) drops. On my dyno plots, you can see the power curve trail off at about that point. It keeps increasing all the way to 3500 rpm, but not very rapidly. If I were racing, I would want to shift at that roll off point, or around 2800 rpm.
If performance is your goal, you want to operate near the maximum power point, which will be above the maximum torque point. If efficiency is your goal, operate near the maximum torque point.
I should have an experimental turbocharger installed next week that will let this thing breathe up to 3500 rpm. I think big numbers are possible with good airflow at 3500 rpm. Planning to go to Montana in a coupla weeks...;)
DA BIG ONE
06-30-2006, 16:32
I want to thank all of you for the expert input, mine is just so, so but the rest of you make sense of it.
jspringator
06-30-2006, 16:39
Will it hurt a high mileage motor (like mine) to run all day in 3rd at 2800 RPM? Mine does seem to pull best like this, but I have avoided it because of fear of blowing it up. BTW, I tow a little less than 9,000 lbs. I am not greatly concerned about gas mileage, but don't want to get stranded on vacation.
john8662
06-30-2006, 17:57
As discussed, the 45mph is the lockup point on the 4L80E with 4.10's and 245's.
I like that lockup point and want to maintain it during the swap to 3.42's and 265's (at the same time).
But, one thing I don't like is that once up to speed at say 65mph and above, I don't get a shift out of OD, so passing is done with boost and fuel.
So, my question...
If you use the vss modifier and I leave my VSSB at the stock 4.10 setting, will I still see a no-shift out of OD at 65+?
Hmm.
TurboDiverArt
06-30-2006, 18:11
As discussed, the 45mph is the lockup point on the 4L80E with 4.10's and 245's.
I like that lockup point and want to maintain it during the swap to 3.42's and 265's (at the same time).
But, one thing I don't like is that once up to speed at say 65mph and above, I don't get a shift out of OD, so passing is done with boost and fuel.
So, my question...
If you use the vss modifier and I leave my VSSB at the stock 4.10 setting, will I still see a no-shift out of OD at 65+?
Hmm.
I'm not sure how the 4.10's work. The 3.73:1's lockup the converter at about 47-48, which is pretty close to the 45's you now have. At 65MPH it'll drop out of OD. it'll drop out of OD at 75 if there is enough load like when you have a trailer in tow up a hill.
Art.
moondoggie
07-01-2006, 14:30
Good Day!
On reflection, I really don't care much about the shift points, I just wish the TC would lockup at a lower speed, & have more hysteresis in that lockup speed.
I sure wish I'd known about these trucks as they were being introduced in '94. I think a guy could have written some killer code to allow changing many different parts of the algorithm to suit the owner. I would REALLY have liked to integrate my Gear Vendors Aux. OD into the PCM.
Blessings!
(signature in previous post)
TurboDiverArt
07-01-2006, 18:05
Boost is the reason you feel the lessening acceleration. The problem is the small housing and nozzle on the GM-4 turbine. Above about 2800 rpm, it simply cannot flow enough to keep up with the engine. The backpressure blows the waste gate open (even against full vacuum straight off the pump...as I've been running for a year now) and the turbine rotor holds constant speed. I've plotted data points on the compressor map and the compressor is following a constant speed line above 2800.
This means that boost falls off even as total flow increases. Power falls as well.
I thought my turbo was a GM-8? I thought the GM-8 came on the newer trucks. Mine being a 1999 I assumed mine came with it. Maybe the GM-8's only came on the Hummers?
Thanks,
Art.
john8662
07-01-2006, 18:34
Art,
RJ's only had experience with the GM4 turbo which was used from 94-95. Being that you have a '99 you should have the GM8. I do personally believe there is a little better flow with the GM8, but the internals of the turbo are almost identical, the change is in the exhaust side. GM5 and GM8 are almost the same turbo too, except for a better wastegate bushing on the '8.
TurboDiverArt
07-01-2006, 19:42
Art,
RJ's only had experience with the GM4 turbo which was used from 94-95. Being that you have a '99 you should have the GM8. I do personally believe there is a little better flow with the GM8, but the internals of the turbo are almost identical, the change is in the exhaust side. GM5 and GM8 are almost the same turbo too, except for a better wastegate bushing on the '8.
So, has anyone seen a compressors map of a GM-8? In our motors where does the turbo run out of steam? On mine it appears that at high RPM's it
DA BIG ONE
07-02-2006, 04:37
[QUOTE=TurboDiverArt]So, has anyone seen a compressors map of a GM-8? In our motors where does the turbo run out of steam? On mine it appears that at high RPM's it
TurboDiverArt
07-02-2006, 05:35
Art, The GM-8 exhaust turbine "exhaust outlet" is some of the limiting factor needing some porting. How much porting? It's more a matter of how much risk one is willing to take making walls too thin.
Some say the elbow after the gate is an issue, then some smoothing out of its inside surfaces are in order.
I really thing wee need those bigger Holset 35, 40 turbo's providing we stay out of the surge line, and keep boost at a level of 15+- psi @ intake.
If the GM-8 seems to run out of steam at 2800, were does a GM-8 run out with a free flowing exhaust? Mine definitely seems to lose it by 3100, maybe 3000.
Art.
ronniejoe
07-02-2006, 08:52
The rotors on a GM-4 and GM-8 are identical. The only difference is a slightly better compressor housing and a slightly better exhaust elbow. The waste gate was moved out of the exhaust housing into the elbow on the 8's and I've been told that the elbow is more efficient. With that said, I don't think you'll see significant performance differences between the two. The wastegate move was to improve reliability of the bushing (mine failed) and had nothing to do with performance.
I have an outline map of a the GM series compressors...it has no detail and IHI will not even respond to my inquiries. The other manufacturers have been very responsive to my questions.
It is fair to take my comments as being applied to the GM-X series in most cases.
My main comment here was to clarify the relationship between peak torque and peak power and to give you some of the rationale behind choosing shift points. The turbo talk was simply to help explain some of your observations.
TurboDiverArt
07-02-2006, 18:13
The rotors on a GM-4 and GM-8 are identical. The only difference is a slightly better compressor housing and a slightly better exhaust elbow. The waste gate was moved out of the exhaust housing into the elbow on the 8's and I've been told that the elbow is more efficient. With that said, I don't think you'll see significant performance differences between the two. The wastegate move was to improve reliability of the bushing (mine failed) and had nothing to do with performance.
I have an outline map of a the GM series compressors...it has no detail and IHI will not even respond to my inquiries. The other manufacturers have been very responsive to my questions.
It is fair to take my comments as being applied to the GM-X series in most cases.
My main comment here was to clarify the relationship between peak torque and peak power and to give you some of the rationale behind choosing shift points. The turbo talk was simply to help explain some of your observations.
Thanks for the info, it's good information! It definitely seems that the stock turbo putters out in the 3000 range. This is why I thought the shift point should be at about that point. It just seems to take forever to get from 3000 to 3500. Now if you had a turbo that would pull all the way up to 3500 RPM
ronniejoe
07-02-2006, 19:59
[quote=TurboDiverArt]Now if you had a turbo that would pull all the way up to 3500 RPM
john8662
07-02-2006, 23:29
Hold that thought...
You just couldn't resist could you!
ronniejoe
07-04-2006, 12:16
Will it hurt a high mileage motor (like mine) to run all day in 3rd at 2800 RPM? Mine does seem to pull best like this, but I have avoided it because of fear of blowing it up. BTW, I tow a little less than 9,000 lbs. I am not greatly concerned about gas mileage, but don't want to get stranded on vacation.
My experience has shown that egt's run high under those conditions. I prefer to run in OD at higher boost levels where things stay cooler.
TurboDiverArt
07-04-2006, 18:01
My experience has shown that egt's run high under those conditions. I prefer to run in OD at higher boost levels where things stay cooler.
I'll agree with that! RPM's and low boost equals high EGT's. Before the intercooler install, when the transmission would downshift out of OD and the RPM's would go up to the 3000 range the EGT's would climb dramatically and quickly. Higher boost helps to cool things down but isn't the real solution to the problem.
That was why in a previous post I was suggesting hacking the VSSB to read 4.10 gears when mine were in fact a higher ratio. If setting it to 4.10 gears helps to keep the converter locked and/or keep it from dropping out of OD then I think it's a possible viable modification. I believe one poster above said that with the 4.10 gears it was very difficult to drop out of OD over 65-70 MPH. With 3.73 gears that's about 2200-2400 RPM's. That's a nice RPM range for a lot of boost when towing. On mine if it kicks down out of OD at 65-70 that means like 3100 RPM's and the trucks just not pulling anymore, only generating EGT's.
Art.
DA BIG ONE
07-05-2006, 03:50
It has been suggested that I try and run my burb in 3rd only to see if mpg results get better.
TurboDiverArt
07-05-2006, 16:12
It has been suggested that I try and run my burb in 3rd only to see if mpg results get better.
You thinking you got too little gear? With the oversized tires you're probably at what, 3.08's? Probably real good at 50 MPH but maybe the engine's got to work too hard at highway speeds with wind resistance. What do you get at 65-70? On straight highway I'll get about 18.5 MPG and 14 towing on relatively flat highway.
Art.
dieseldummy
07-05-2006, 20:39
WOW!! I just read through this thread to catch up and find myself wondering what turbo selection has to do with a gear swap for MPG??? Unless one has an interest beyond MPG.
On my '93 I started out with stock 245/75/r16 tires and 4:10 gears. That would net a consistent 15MPG around town. When I swaped to 285/75/r16's I gained nothing... probably lost 1mpg truth be known. I always atributed it to added rolling resistance. I've always been under the impression that swaping out gears doesn't have that effect because rolling resistance is the same and the only difference is how long it takes to get rolling. That's what I got out of this thread thus far, am I somewhat correct?
ronniejoe
07-05-2006, 20:44
While I agree the turbo stuff drifted a little, it was originally on subject.
The conversation had to do with engine speeds and ideal shift points for economy. There were some questions that ended up bringing the discussion around to performance as well. Then the subject of falling flat above 2800 rpm... That led to turbos... That led to discussions of power... That led back to economy...
You get the drift.:D
dieseldummy
07-05-2006, 21:22
Vicious circle ain't it...;)
TurboDiverArt
07-06-2006, 03:37
WOW!! I just read through this thread to catch up and find myself wondering what turbo selection has to do with a gear swap for MPG??? Unless one has an interest beyond MPG.
On my '93 I started out with stock 245/75/r16 tires and 4:10 gears. That would net a consistent 15MPG around town. When I swaped to 285/75/r16's I gained nothing... probably lost 1mpg truth be known. I always atributed it to added rolling resistance. I've always been under the impression that swaping out gears doesn't have that effect because rolling resistance is the same and the only difference is how long it takes to get rolling. That's what I got out of this thread thus far, am I somewhat correct?
I think as Ronniejoe said the subject drifted a little but did cover a lot of interrelated issues.
I don't think any of the above topics concluded that a gear reduction has an adverse effect on mileage. I think yours is the only one that has stated that reducing the gearing from 4.10 to 3.73 via. tire change adversely effected mileage. I think DaBigOne's poorer mileage may be because he's reduced a little too far and was using an aggressive tread pattern. Tread pattern has a big effect as does the width of the tire. If you go bigger, any benefits may be negated if you use a really wide tire and/or aggressive tread pattern.
I believe comparing stock trucks to stock trucks it's been proven that 3.42's get better mileage than 3.73
dieseldummy
07-06-2006, 07:22
I never corrected the VSSB/speedometer, but made the correction in my head. If I wanted to travel 65 mph I would put the speedometer at 60 mph. Whenever I filled up I corrected the number of miles on the odometer to make up for the larger tires. The tread pattern is not that aggressive, the tires are yokohama geolander at+2.
TurboDiverArt
07-06-2006, 08:48
I never corrected the VSSB/speedometer, but made the correction in my head. If I wanted to travel 65 mph I would put the speedometer at 60 mph. Whenever I filled up I corrected the number of miles on the odometer to make up for the larger tires. The tread pattern is not that aggressive, the tires are yokohama geolander at+2.
Huuumm, strange I think. I would think you'd see a fairly significant difference going from 4.10's to an equivalent 3.73's if you were traveling at the same speed. I'd think with 4.10's you probably don't go long distances at over 65 MPH. You'd probably be screaming along at about 2300-2400 RPM's. I just wanted to make sure you were not calculating mileage at 60 MPH with the 4.10's and comparing it to 70 MPH with the 3.73's. Although the RPM's may be similar you are going to experience a significant amount of additional wind resistance at 70 that you would not have at 60.
I
Hi Diesel Dummy;
I agree that things did "drift" of topic a bit. Any way my thoughts on the worse MPG for larger tires is that with wider tires you have besides more rolling resistance you also have more areodynamic drag with a larger tire face in the slip stream. The other with a "taller" stance on your truck with the taller tires you also increase the "drag" from the under carriage of the truck.
This all adds up.
Holy smokes! Go away for a couple of days and miss 4 pages of posts!
The hot button is DaBigOne keeps saying his shift points changed. I'm saying the way they are computed is not based directly on road speed and they have not changed; the road speed is what changed. I never meant the factory settings were optimal. To each his own.
On that subject, now that he's got them "back where they belong" he's thinking of driving in 3rd all the time. Anyone else see any irony here? ;)
Re optimal shift points, I always thought you wanted to be where the decending torque curve of he current gear crosses the ascending curve of the next gear. No?
ronniejoe
07-06-2006, 13:28
If you want to accelerate down a race track as quickly as possible, you want to shift where the power curves cross from gear to gear.
If you want to accelerate down a race track as quickly as possible, you want to shift where the power curves cross from gear to gear.
I'm sure you are correct, but wouldn't the torque curve give you the strongest acceleration, hence the highest trap speed? (Bear in mind I've retired all my math skills past basic algebra... ;) )
DA BIG ONE
07-06-2006, 14:24
The hot button is DaBigOne keeps saying his shift points changed. I'm saying the way they are computed is not based directly on road speed and they have not changed; the road speed is what changed. I never meant the factory settings were optimal. To each his own.?
Perhaps, I'm just thick headed so bear with me will ya?
I changed out to 3.42 gears from 4.10's frt/back, using stock sized tires 245/75/16.
I hack the vssb to correct speedo and shift points/lockup go to higher rpm's and speed points and od/lockup goes from 45 w/4.10's to 55 mph w/3.42's.
Now I only hack the vss only to correct the speedo and the shift points lockup, od/lockup all stay as they were w/the 4.10's, same rpm's same speeds.
So, I guess I'll remain confused on this one until someone can drill it into my thick skull........................
john8662
07-06-2006, 15:58
For what it's worth, I'm with you DA BIG ONE!
I'd like to try the same mod, but keeping the lockup at the same speed on the speedometer.
ronniejoe
07-06-2006, 18:33
Torque is basically work, or energy...they both use the same units.
Power is the rate of doing work or rate of energy usage. To go down the track quickly, you want to do the work quickly.
john8662
07-06-2006, 20:57
You going to be racing that burb down the track Ron?
DA BIG ONE
07-07-2006, 02:31
Biggest lesson learned with much $$$$$ in my gear changeout is that you get good mpg until you start going larger tire diameter & width, then you arrive at the same spot you paid so much to get away from in the first place.
So, perhaps leaving the 4.10's and just doing the tire change I might have been happier.
All, in all the burb is a keeper.
TurboDiverArt
07-07-2006, 03:04
Hum, food for thought. I have a set of H2 rims on the way to me. I was planning to put slightly bigger tires on them and increase the diameter by about an inch and a half. This would not have reduced the gears down to 3.42's but probably to about 3.55's. The width would have increased by 0.4 inches. Now I'm wondering if it's worth it. If I
DA BIG ONE
07-07-2006, 04:12
I'll add that my burb w/it's mods is happy w/3.42's and stocked sized tires. These 6.5 td's aren't like the old 6.2's in that the 6.2 4x4's were ok w/3.08 gears.
Hi DA BIG ONE;
Thankes for all the great input about gear changes. Your shift points changed on a per MPH basis but I bet are about the same on a RPM basis, that's what happened with me when I changed to 3.42's. This makes sense for the tranny controller isn't concerned about speed across the ground but engine speed for shifting. OD lock up happens about 1600 RPM if I am using very modest acceloration. That was about 47 -48 MPH with the 3.73 gears now OD lockup happens about 52-53 MPH with 3.42 gears but still 1600 RPM.
If lock up happened for you still ~ 45 mph that would be too low of RPMs and would "lug" the engine. It appears your thining in MPH's instead of RPM's.
I hope this helps you out. I appreciate you tire size observations it has helped me from going to a larger tires.
Yeah, what 16ga said. If there was any increase in RPM relative to shifting it was due to the fact that you were harder into the pedal as a concequence of the taller gearing.
I just find it ironic that you worked so hard to get the shift points back up to the original speeds and now are contemplating driving around in 3 instead of OD. Could it be that your upshifts are happening too early? ;)
RJ, you may be concerned with doing work faster. I gave that up a while ago... If time is an issue these days, I usually opt for less work. ;)
a = dV/dt
TurboDiverArt
07-07-2006, 13:36
Does anyone have any experience changing the gearing using tire only but not reducing the effective gearing past 3.42. I think what DaBigOne was saying is that reducing the gearing to 3.08 is too much. I could choose a tire that reduced my gearing to about 3.50-3.55 I estimate. Stock tire is 30.5" tall and a 255/75/17 is 32.0 (but .4
moondoggie
07-07-2006, 16:17
Good Day!
"I think what DaBigOne was saying is that reducing the gearing to 3.08 is too much." (Following based on 3.08 gears, NOT what DaBigOne may or may not have meant.) For my 95 pickup, with 4L80-E in OD, GV (Gear Vendors Aux. OD) engaged, & 4% oversize tires, that's my effective ratio. It pulls it just fine. In fact, the last couple races we went to, I started pulling our trailer (looks like the US Cargo SM727TA2 (http://www.uscargo.com/uscargo/products/enclosed/snowmate.asp) [Click in colored text] except it's 25' long instead of 27') in double OD * with no problems; I only did this if cruising 65 mph or more. As long as I anticipated the roll of the highway with my footfeed (the cruise would let it lag too much, causing a downshift, causing my tranny to code due to how I've got the GV electrically hooked up (non-standard)), it worked great, & my truck's bone stock - it's never even been timed in my ownership (80K miles to present).
I don't recommend doing this, but from time to time I'll be in double OD at 50 mph, which is ~ 1250 rpm. Within the range the PCM allows before commanding a downshift, it cruises & accelerates without a hitch.
You guys are just jealous because us GV folks are only turning ~ 1750 rpm @ 70 mph. ;)
Blessings!
(signature in previous post)
*double OD: What us fortunate GV owners call it when the tranny's in OD & the GV is engaged - 0.75 (I think) for the 4L80-E, 0.78 for the GV.
DA BIG ONE
07-07-2006, 17:55
It's been a costly ride changing out gears, wheels, & tires.
I'm thinking 3.42:1 w/stock sized tires is about the limit w/everything going down hill from there.
The third gear on highway idea came from the fact that the motor is no longer in it's best rpm range w/my setup. Defeated, or?
moondoggie
07-07-2006, 18:38
Good Day!
"Biggest lesson learned with much $$$$$ in my gear changeout is that you get good mpg until you start going larger tire diameter & width, then you arrive at the same spot you paid so much to get away from in the first place." I ran 235/85R16's on my pickup for a few years, which are ~ 4% taller than stock & 10mm/.4" narrower. As much as I take care about recording mpg, I can't determine what if effect they had on my mpg. So, I'm switching back to stock (245/75R16's) on both 95's.
Blessings!
(signature in previous post)
Warren96
07-19-2006, 13:16
'' As long as I anticipated the roll of the highway with my footfeed (the cruise would let it lag too much, causing a downshift, causing my tranny to code due to how I've got the GV electrically hooked up (non-standard)''
Moon ....,
What does that mean ....isn't the Gearvendors made for your truck?
Stratosurfer
07-20-2006, 04:48
My question to the group is this: I can get a Gear Vendors installed turn key in Houston for $3,400, about double the price to lose my 4.10 gears. I have only heard/read glowing reports on how the 6.5 TD responds when given an 8 speed transmission that is corrected down to 3.08 final drive when not towing.
I am on the fence as to what to do with all this data y'all are pouring out on installing smaller gears against the future possiblilty that I will obtain the bumper-pull portable Texas Ranch House/pontoon barge (Texsas Reservoir Yacht) of my dreams and need to tow 9,000+ lbs once in a little while.
I like the idea of the gear change for the component of simplicity, I lile the idea of the second transmission for the reportedly phenomenal results.
Anyone opine on this conundrum?
As well Texas DPS is slowly changing the speed limits in the 'remote' areas (I live in a remote area) to 80MPH. I will somehow feel deprived if my RPM's are so high at 80 MPH as to force the stereo to maximum DB's and I still can't keep up with the lawyers from Austin in thier sporty German Turbo Panzerwagens.
Towing, MPG and MPH; is Gear Vendors the only true solution to all these?
moondoggie
07-20-2006, 06:12
Good Day!
"...I've got the GV electrically hooked up (non-standard)." I didn't expand on this previously, in the name of saving space in case no one was interested.
Normally when a GV is installed, there is a second VSSB used. One supplies the PCM with the shaft rpm signals received from the tranny input & output shafts & massaged by the VSSB. The 2nd VSSB is fed from an additional shaft rpm sensor, identical to the GM units, on the GV output shaff. Then the wire that feeds the speedo/odo is disconnected from the 1st VSSB & connected to the 2nd.
Mine's wired different. I only use one VSSB & don't use the tranny's output shaft sensor, just the GV output shaft sensor. Because of this, I have to make sure I never use the GV except in OD (tranny). When I mess up on this & downshift the tranny while the GV is engaged, the PCM figures there's slippage (input & output shaft rpms don't match the gear ratios in the tranny, which the PCM knows) & commands full tranny fluid pressure, causing hard shifts.
Why does this work? For some reason, the PCM never checks for slippage when the tranny's in OD.
Why did I do it? In the GV-approved hook-up, as soon as the GV is engaged, the PCM thinks the vehicle is going 0.78x the speed it's actually going. This tends to make the truck downshift a lot more than I like. As mpg is my only hobby, I like my truck to get into top gear & stay there.
"I can get a Gear Vendors installed ...Anyone opine on this conundrum?" Send me a private message with your real email address & I'll send you an email with a spreadsheet attached that will allow you to make a reasonably well-informed decision. This spreadsheet allows you to type in what ANY mod you might be considering costs, what you get for mpg now, what you guess you'll get after the proposed mod, & the price of fuel, then returns exactly how many miles it will take to pay for your mod. This works REGARDLESS of what mod you're contemplating.
My best guess is that my mpg increased ~ 2 mpg after installing the GV. The added benefit is that you literally can't tell you're driving a diesel at highway speeds. With the addition of 4% oversize tires, I'm only turning 2000 rpm @ 80 mph. (A GV in front of 4.10 gears will give you 3.20 effective ratio, NOT 3.08 - 3.08 is what I've got with the addition of the 4% oversize tires.)
Another alternative is to build a mondo strong & powerful 6.5 like RJ's done, then you can have taller gears all the time, although I'm not sure anything taller than 3.73 is readily available for 14-bolt full-floaters. (I'd suggest a search - this has been hashed out B4; I didn't pay much attention as I already had my GV.)
Blessings!
(signature in previous post)
DA BIG ONE
07-20-2006, 13:11
My question to the group is this: I can get a Gear Vendors installed turn key in Houston for $3,400, about double the price to lose my 4.10 gears. I have only heard/read glowing reports on how the 6.5 TD responds when given an 8 speed transmission that is corrected down to 3.08 final drive when not towing.
I am on the fence as to what to do with all this data y'all are pouring out on installing smaller gears against the future possiblilty that I will obtain the bumper-pull portable Texas Ranch House/pontoon barge (Texsas Reservoir Yacht) of my dreams and need to tow 9,000+ lbs once in a little while.
I like the idea of the gear change for the component of simplicity, I lile the idea of the second transmission for the reportedly phenomenal results.
Anyone opine on this conundrum?
As well Texas DPS is slowly changing the speed limits in the 'remote' areas (I live in a remote area) to 80MPH. I will somehow feel deprived if my RPM's are so high at 80 MPH as to force the stereo to maximum DB's and I still can't keep up with the lawyers from Austin in thier sporty German Turbo Panzerwagens.
Towing, MPG and MPH; is Gear Vendors the only true solution to all these?
If you can use the GV it would be a better option, and doubtful the tranny would search for the right gear like it does with only the 4L80e and 308's. The gear vendor was my first choice but never an option for me because of the NP246 AutoTrac.
I'm thinking the GV w/4.10's is the right route.......
Posted: 80mph= 90+ for most
If I understand right, my 4.10 gears effective ratio with 235/85R16s is about 3.73 (plus or minus). And if I change to 3.73 it would be about the same as 3.42 and going to 3.42 it would be about 3.08? Currently at 70 mph I am turning about 2200 - 2300 rpms.
My K3500 dually has the NV4500 with the low 1st gear. I recently found a couple large chipped pinion gear teeth and I am contemplating changing to 3.42, but I am wondering if that will be too high with the 235/85R16 tires. Would I be better off at 3.73? I only tow boats and an open car trailer once in a while.
I would like the GV but it appears the payoff time is very long, the gear sets are about 1/3 the price and a shorter payoff, and I need to do the rear end anyway. I am currently averaging about 19mpg (summer blend) and about 14 mpg towing, and wondering how much better can the mileage get, maybe 2 - 3 mpg?
In short
Lowering the ratio, lowers the RPM - this does not mean lower MPG
This can and will be detrimental to the engine to lug a motor.
Every engine out there has a "sweet" spot for power and were it like to run.
Outside of this area is wear either by friction or poor lubrication, yes even at low RPM
The 6.5 pulls best around 2700RPM
Put in a gear the you can live with and run the engine as intended.
I run 4.56 gears with stock tires, I pull 8000 lbs. However I can only go 75MPH top end, fast enough for me. When the engine runs at 2500 to 2800 it takes alot to slow it down, hills etc. Run the engine at 1500 and your foot will be in the gas pedal more often
Key in all engines for MPG is vacuumm not gearing.
JCM5
Key in all engines for MPG is vaccum not gearing.
How are you thinking this? Turbo's have no vac. Added boost up to 10lbs. 12lbs. max W/O intercooler helps with EGT and better fuel burn.
Your running the same tire set up as I am. Gearing one ratio down will help in the RPM area. This will work with lite towing and needed can tow in 3rd for hills, slow driving, ect. Running with out load will help with mpg. Diesel like the tourqe range over rpm's.:) I wish I could get the mpg you are seeing:( Though I have bed mounted side rail tool box with ladder rack and in bed slide out box. Lot's of weight and not at all areo when it comes to drag. My best is 14mpg.
I do like 85's when it comes to tires. What air psi do you run?
ronniejoe
07-26-2006, 04:44
Diesels don't make vacuum...
Gearing is the answer...
The engine operates with maximum efficiency near its torque peak... For best fuel economy, operated near 1800 rpm. Gearing will let you accomplish this.
Also, slow down. Don't run much over 65 mph.
Why do you think all of the late 70's and early 80's cars suddenly started using really tall gearing?
I calculated with my tires, I will be at exactly 1800 rpm with 3.42 gears at 70 mph, and at 60mph I would be at 1540 rpms using the 5th OD. In the 4th gear at 60 mph the engine would be at 2175 rpm, which is close to what I run now at 70 mph in OD
With 3.73 gears at 70mph the engine will be at 1960 rpms, and at 60mph the engine would be at about 1675 rpms in OD, in 4th the engine rpm would be about 2375.
From what I have read, it appears that I will gain driveabilty, but lose some towability, (is that a word?). Since I have the low-low 1st gear I should be good with the 3.42s as long as I do not increase tire size. Since I am running the NV4500, I can always drive in 4th, or select the gear I need.
It appears the 3.42 gears run the engine in the sweet spot (1800 rpm) at 70 in OD, and at a good (familiar) spot at 60 in 4th gear (2175 rpm) and using OD in town at 35mph it will be close to idle.
Are these calculations correct? Again my tires are 235/85/16, approx 31.75" tall. I usually run the fronts about 60psi and the rears at 65-70psi.
...Since I have the low-low 1st gear I should be good with the 3.42s as long as I do not increase tire size....
This is the setup I had in my '93. It was OK on flat ground towing a 5000' trailer. First is too low for most starts and 2nd is too high if you're on much of a grade. Also, all of the gears are spaced too far apart and you have to really flog it before shifting.
The mileage was great, though. However, if I had it to do over, I think I'd opt for the 3.73 or maybe the automatic.
Running empty it was fine.
For those of you that have gone to 235/85/16 tires how do you like them? Does the taller side-wall lead to more floatiness (is that a word), or other undesireable handling characteristics? What about 265/75/16's? The 265's are about the same diameter as the 235/85's and would look more manly, but I am concerned about the wider tire having more drag. So, for better MPG, with no other changes, should I go 235/85 or 265/75? Of course, the other option is stock - 245/75. BTW, I have 4:10's
Bill
TurboDiverArt
08-01-2006, 08:06
For those of you that have gone to 235/85/16 tires how do you like them? Does the taller side-wall lead to more floatiness (is that a word), or other undesireable handling characteristics? What about 265/75/16's? The 265's are about the same diameter as the 235/85's and would look more manly, but I am concerned about the wider tire having more drag. So, for better MPG, with no other changes, should I go 235/85 or 265/75? Of course, the other option is stock - 245/75. BTW, I have 4:10's
Bill
For what it's worth, tomorrow I'll have 265/70-17's mounted on H2 rims. It's about an inch taller than stock (31.6) and about 1/2" wider section width than stock (10.4
TurboDiverArt
08-01-2006, 16:19
[QUOTE=TurboDiverArt]For what it's worth, tomorrow I'll have 265/70-17's mounted on H2 rims. It's about an inch taller than stock (31.6) and about 1/2" wider section width than stock (10.4
DA BIG ONE
08-10-2006, 03:47
Update. I just pulled the steel rims from the truck. Unfortunately the weight of the steel rim and 245/75-16 is right at 72lbs. If my calculations of what the H2 rim and tire will weigh (265/70-17), it's the about the same. H2 rim weighs 30 lbs and the tire is 41 so they weigh the same. Bummer for finding a lighter wheel combination, at least it'll look good!
Art.
How about update..........
TurboDiverArt
08-21-2006, 03:43
How about update..........
Sorry about that, been off-line for little bit. Towing out to Salem seemed to be good. I got 15 MPG, one more MPG than I did last year. Average speed about 70 MPH. Coming back I was tired and had a friend drive. He doesn't use cruise control so not a fair comparison.
Around town driving it seems to be about the same. I have not taken the truck on a long highway non-towing trip yet.
Art.
Shikaroka
08-23-2006, 07:56
I apologize if this has been covered, but I have a question.
If I want to put in a set of 342s in my 96 Suburban K2500, where should I look? What other trucks can I use the parts from?
Thanks!
Todd
Shikaroka
08-27-2006, 08:18
I just swapped out the stock 16" steel wheels off my 96 Suburban, for a set of aluminum 16" wheels from the newer trucks.
My stock steelies (w/ 245/75/16 tires) weighed about 82 lbs. The aluminum wheels (w/ same size tires) weigh about 54 lbs. That's a difference of 28 lbs. which is pretty substantial when you are talking about unsprung weight.
I can already tell a difference. The truck is certainly peppier. I suspect I will get a little better MPG too, at least I hope so.
Also, since I have the 14 bolt, 10.5" rear end, is 373 the lowest number gear set I can get?
I think I'll be rebuilding my rear end soon.
DmaxMaverick
08-27-2006, 11:08
I just swapped out the stock 16" steel wheels off my 96 Suburban, for a set of aluminum 16" wheels from the newer trucks.
My stock steelies (w/ 245/75/16 tires) weighed about 82 lbs. The aluminum wheels (w/ same size tires) weigh about 54 lbs. That's a difference of 28 lbs. which is pretty substantial when you are talking about unsprung weight.
I can already tell a difference. The truck is certainly peppier. I suspect I will get a little better MPG too, at least I hope so.
Also, since I have the 14 bolt, 10.5" rear end, is 373 the lowest number gear set I can get?
I think I'll be rebuilding my rear end soon.
You can get aftermarket R&P's. Randy's Ring & Pinion (http://www.randysringandpinion.com/) has gears down to 3.21 for the 14 bolt.
Since your truck is a 4x4, you'll need to do the front, as well.
Shikaroka
08-28-2006, 07:37
Thanks!
But, I think 321 might be too low. They don't have anything listed between 321 and 373.
How do I know what gear set I need for the front? Would it be the same as the rear, a 10.5"?
Please forgive my ignorance.
I have been working on cars for over 15 years, but I am new to the 4x4 game.
DmaxMaverick
08-28-2006, 08:55
Thanks!
But, I think 321 might be too low. They don't have anything listed between 321 and 373.
How do I know what gear set I need for the front? Would it be the same as the rear, a 10.5"?
Please forgive my ignorance.
I have been working on cars for over 15 years, but I am new to the 4x4 game.
Give them a call. Tell them what you have, and what you want to do with it. They have options not listed on the website. A 3.42 (common ratio) may be available, but you asked about ratios higher (lower #) than 3.73. There wouldn't be a significant difference between 3.42 and 3.21, and you can adjust final drive with tire size, as well. If you stay with stock tire size and don't tow heavy or frequently, 3.21 may be ideal. Some rigs are as high as 3.08 and loving it.
Shikaroka
08-28-2006, 10:28
Cool, thanks for the info!
3.42 was available from the factory, so it should be available in the aftermarket, too.
6.5 Detroit Diesel
11-15-2006, 17:50
Personally for me, because I use my truck for heavy duty work, the 4.10's are awesome. The 5 speed has the low gear and combined low and 4.10 gears mean this truck could climb a tree without breaking a sweat. Example of this was when I had 60 sixty to sixty-five pound bales on the back and was delivering up a mountainside. The truck hauled the whole way without having to rev it high. Once there, I had to turn around on a hill and back over the curb. Did both things without having to touch the throttle. Just let the clutch out. My previous hauling truck was an older Ford with 2.75 gearing and big block six. I had to have the engine screaming to get power out of it with a ton on the back. The 4.10's are so much better for pulling power. I've also had the truck at just over 170 kmh on a road trip, but at this point it was howling. (Not recommended again.) So for a work truck, my points go to the 4.10 gearing.:D
I got 93 4x4 5sp with 4.10, i found a 2-3in lift for $150 that i plan on putting 33x12.50 on a 17x8 rim which should help me with highway mileage. What do you guys think?
DA BIG ONE
02-22-2007, 05:22
I got 93 4x4 5sp with 4.10, i found a 2-3in lift for $150 that i plan on putting 33x12.50 on a 17x8 rim which should help me with highway mileage. What do you guys think?
Drag will increase w/lift. I run 33"x11.5" w/o lift happy w/it...........
moondoggie
02-22-2007, 08:27
Good Day!
As above, lifting increases drag. Those tires are pretty wide, which will also increase rolling resistance. Look at the high-mph vehicles - they like to put skinny hard tires on them to minimize rolling resistance.
I think it'll look cool & cost more to drive.
Good Luck & Blessings!
well i am really set on getting these 17x8 rims, and was really set on getting 33x12.50 MT MTX. I like tall skinny tires but cant find any with a all-terrain tread with a skinny tire. Could you guys help me out. Also the tires have to be somewhat cheap
baker2acre
02-26-2007, 13:09
Boy, that sounds like the ideal lady... tall.... skinny... likes mud, and CHEAP!!!! :D
bmp34, I'm just messing around.... honestly though, specialty and economy don't usually get put on the same invoice. In the same token, I don't know that I've seen an "aggressive" tread on a low profile tire either. Low profile's are usually reserved for "high-performance street" use where the need for low tire roll from hard cornering supercede the need for shock absorbtion of off-road impacts. However, I've been wrong before, so I'll take a look-see.
Well i see yokahama makes some pretty tall skinny tires but i cant figure out the sizes, the only ones i know how to read are when they say 33x12.50 not 305/75r or whatever
DmaxMaverick
02-27-2007, 01:46
Well i see yokahama makes some pretty tall skinny tires but i cant figure out the sizes, the only ones i know how to read are when they say 33x12.50 not 305/75r or whatever
The tire sizes are really pretty simple. Stop reading here if you are scared of a little math.
For example, LT305/75R/16. The LT is Light Truck, P is Passenger, and R is Radial.
The 305 is the tread width in milimeters (305mm). The 75 is the height of the sidewall, as a percentage of the tread width (75% of 305mm). The 16 is the wheel diameter, in inches.
So.....305mm = ~12", and the sidewall height is ~9" (75% of 12"). There are 2 sidewall heights (above and below the wheel), so there is a total of 18" of sidewall. Add the wheel diameter, and the tire height is ~34". Or....34x12x16. The actual numbers won't be exact, but neither are the tire manufacturers stated sizes.
I could have given you a link to a tire size calculator, but didn't (obviously). Give a man a fish, and he'll eat for a day. Teach him to fish, and he'll eat for a lifetime.
"Give a man a fish, and he'll eat for a day. Teach him to fish, and he'll eat for a lifetime."
DMAX- That is true, but it does depend on the fish. !! I have found them very uncooperative. !!!
DmaxMaverick
03-01-2007, 09:09
"Give a man a fish, and he'll eat for a day. Teach him to fish, and he'll eat for a lifetime."
DMAX- That is true, but it does depend on the fish. !! I have found them very uncooperative. !!!
No problem. I'm not going anywhere. If it doesn't work out the first time, we'll still be around, and I always have lots of fish. You can live on carp, if you have to.
jasondmann
04-01-2007, 18:28
Another good option for tall skinny tires are military tires. They have a very agressive tread pattern but are extreemly hard (something like 10 ply) I would only recomend if you are going for the look not performance, however they will never wear out even when used on road.
Jason
PS: This is my first post, these forums have a lot of info and it seams that I have a lot of reading to do... Anyway I am currently runing 285/75/16 through 3.73 with a 2" lift, I'll let you know how fuel economy is in a couple of weeks.
DA BIG ONE
04-05-2007, 03:33
After all is said and done I admit I would have saved $$$$.+ dollars not changing out gears on my 4x4 burb to 3.42's from 4.10's.
Been through 2 sets of GoodYear MTR's stock and 285's great of road but a waste on road. Now using 285 GoodYears SilentArmor like the quiet sure footed ride on road and they work good in sand.
MPG is not consistant unless I drive at slower speeds, but I'm now geared for 70+ mph and the drag is a drag.........................
I'm actually thinking seriously about going back to 4.10's maybe 4.58's w/taller tires................
I doubt your TCC is ever locked...
DA BIG ONE
07-07-2007, 15:12
Been mulling this around for some time now and decided to go back to the 4.10's.
Will have the 3.42's on the market soon, frt 9.25" ring w/pinion, rear 10.5" ring w/pinion.............
try the resister to fool the tcc lock up, stay in 3rd gear, tcc should stay locked above 45 mph, don't use 4th on a hill, down shift manuel...
2nd gear will also lock tcc about 32 mph...
but you have to shift manuelly, as Trans will be in high pressure mode,
Need to shift like it's a std shift, un-throttle and match rpm to drivetrain.
I installed a sw for the TCC lock up, and a sw for the 3-4 shift,
2 sw's by the console to control shifting...
DA BIG ONE
07-08-2007, 17:21
try the resister to fool the tcc lock up, stay in 3rd gear, tcc should stay locked above 45 mph, don't use 4th on a hill, down shift manuel...
2nd gear will also lock tcc about 32 mph...
but you have to shift manuelly, as Trans will be in high pressure mode,
Need to shift like it's a std shift, un-throttle and match rpm to drivetrain.
I installed a sw for the TCC lock up, and a sw for the 3-4 shift,
2 sw's by the console to control shifting...
I'd like to try this, what's involved?
50 ohm resister accross the tran emp sensor to ground, through a switch.
this will allow the TCC to lock up at 40 mph for a 3.73 gears,
allow 2nd to lock the tcc at 28 mph for 3.73 gears.
4th , mph not affected,(abot 50 mph tcc lock up)
But the TCC will not unlock, will hold untill down shift , ( very harsh shift ) thats why you need to manually shift,,,
Note all all your speeds will be about 10 per cent higher, with the 3.56
( there are posts on the resister. ).....
for the 3-4 gear shift, need a switch in one of the 3 shift control lines,
that go to the trans,leave in 4th, open switch and it will downshift to 3, close for upshift.
I will have to look in my manuel to find which wire it is, will get back to you,
Note: if you forget and leave in 4th lock out ( 3rd gear, sw open )
and restart engine, a code sets that makes a harsh shift,,,
I was working on a 2-3-4 shift box, with a lock out relay, to prevent
the code problem but sold the truck.
If you have a code reader, setting code is not a problem as a code clear resets it.
will get back with more info..
Shikaroka
08-03-2007, 13:30
I have read most (if not all) of this thread, but I am still a bit confused.
I just swapped out my 4.10s in the Burb for some 3.73s. I rarely tow and never very heavy. I was looking for some lower revs on the interstate and my rear end needed rebuilt anyways.
I checked my speed with a handheld GPS and it appears as though I am actually going about 3-5 mph faster then my speedo claims.
Do I need to "Hack the VSSB"? Or, maybe get a signal modifyer to hack the VSS? I'd like to have my speedo be more accurate and I'd like to have the TC lockup a little sooner (for economy if possible). What should I do? What's the best compramise?
Any advice/help would be appreciated.
Thanks!!
Hacking the VSSB can correct the speedometer. The TCC lockup is based on engine speed (torque) not road speed. No easy way to hack it and it probably isn't a great idea. If you did hack it you'd want it to lock up earlier only under very light load conditions, which may result in it going in and out of lock annoyingly often...
Shikaroka
08-03-2007, 16:23
See? I am confused.
So, is hacking the VSSB the best (maybe easiest/cheapest) route?
turbotim
08-04-2007, 19:10
I'm new here and tried to read through this thread before asking...I recently picked up a "95 3500 HD 2WD dually w/19.5s that has a 4L80 and a Dana 80 rear diff. that according to the tag it is 4.63 and noticed everyone else seems to have 3.42,3.73,or 4.10. It needs a rebuilt 6.5L and wasn't running when I bought it, so I have no idea how it is at highway speed or the mileage. I'm in the process of building a dump bed for it, and it won't see speeds above 55mph very often and will be used to tow on occasion. Does this sound like the correct ratio for this truck and it's intended use? I apologize if this is a dumb question, but I'm new to all of this... /// tim
mr. monte
08-04-2007, 20:29
for that diameter tire, sounds right
Hacking the VSSB is the way to correct the speedometer. The TCC lockup speed is best left alone.
93GMCSierra
09-14-2007, 21:54
just a couple of questions, I have a 5 sp manual trans the shifter was labeled
L 1 2 3 OD
However I can drive in OD at 23 mph with out lugging an even have some torque on acceleration an at 65 mph my tach is about 26-2700 RPM. When really pushing the truck I hit 90 mph at 4000 which is were it seems to have a rev limiter, which is good as I was not intending to blow the motor.
Now my questions are this, why do my RPM's seem alot higher then others with the same set up?
Oh an when I got the truck it had stock sized tires, 245/75/16 steel rims, now has 265/75/16's still steel rims.
My speedo has not been corrected however the difference between its mark an a traffic radar checker is at most 2 mph at 45 mph
TurboDiverArt
09-15-2007, 05:07
just a couple of questions, I have a 5 sp manual trans the shifter was labeled
L 1 2 3 OD
However I can drive in OD at 23 mph with out lugging an even have some torque on acceleration an at 65 mph my tach is about 26-2700 RPM. When really pushing the truck I hit 90 mph at 4000 which is were it seems to have a rev limiter, which is good as I was not intending to blow the motor.
Now my questions are this, why do my RPM's seem alot higher then others with the same set up?
Oh an when I got the truck it had stock sized tires, 245/75/16 steel rims, now has 265/75/16's still steel rims.
My speedo has not been corrected however the difference between its mark an a traffic radar checker is at most 2 mph at 45 mph
What kind of gears do you have in the rear? It's either steep gears or your tach is off. 4000 RPM's seems pretty high. My engine has pretty much quit at 3500.
Art.
93GMCSierra
09-15-2007, 06:49
What kind of gears do you have in the rear? It's either steep gears or your tach is off. 4000 RPM's seems pretty high. My engine has pretty much quit at 3500.
Art.
I have not had the opportunity to find out yet, nor which transmission it is. Or is there only 1 5 spd they put in these trucks?
There was only one trans in '93 for the 6.5. Don't know if the 6.2 was the same or not. Chances are your alternator was swaped and has the wrong pulley. This throws the tach off. 4000 RPM is above the governor set point.
93GMCSierra
09-18-2007, 18:53
Has anyone ever replaced the stock 5 spd with a 6 spd?
6.5 Detroit Diesel
02-07-2008, 16:49
I know a few people who have swapped the trannys. The Dodge trucks have the NV5600's which is the 6-speed. I think one of the biggest things would be finding out if the bellhousing from the 4500 will bolt onto the 5600.
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