Max fuel economy for the 6.5TD

[ees]

Good to know I am not alone. I also have 3.73s, but I have new injectors. My next step is water injection because I can feel a big difference on warmer days. I have Heaths turbo master? (spring loaded waste gate control) set at stock levels, but I still think I am loosing power from intake temps.

[More Power]

Things like engine rpm, vehicle weight & drag, and driving strategies for max fuel economy will apply to just about any light diesel engine. Our vehicle choices affect weight and drag, and have an effect on fuel efficiency.

I think you'll be surprised at what components are available for all 6.2/6.5 diesels (EFI and MFI) that were designed to improve fuel economy, and we'll be discussing all of them here. Some components you may already know about, but there are a few you probably don't… At least not yet!

Jim

[ogrice]

The Max MPG project uses a 72 El Camino. I have a 56' Ranchero that I wish to put a 6.5td or a 7.3psd in. Under the hood is a 352 FE, and the car has been sitting for the last 20+ years in the garage. Big project, a full restoration, but i'm going to do what it takes to get it back on the road.

[Robyn]

In reading here I see a lot mentioned about back pressure. If your engine is fighting back pressure you need to address it. The muffler in stock rigs is most likely a big part of this as well as the catylitic converter. Now if you live in an area that monitors this stuff you cant remove it but there are better units that will flow better. Take for example the big trucks, we run 500 HP caterpillars in our big trucks and they breath out through a 5 inch main from the turbo into a Y pipe and split to two 5 inchers up the stacks and out the top. There is very little back pressure here at all.
If you are seeing more back pressure than boost you need to be opening up the exhaust to let the little beastie breath. The retained heat alone is not doing the engine any good.
Just a thought.

[Marty Lau]

How about adding AIRTABS, http://www.airtab.com/
they claim a 4-8% increase of MPG with them. If your getting 25MPG that is a full MPG increase. I been think about adding this to my truck for
S's&G's.

[Truckie117]

Hey Guy's
I am jelous of the milage. I run stock and I mean really stock.I calculate milage every time I fill up and usally get 15.5 to 16.5 for all around diriving hiway street NY bumper to bumper 495 stuff. The best milage I got was when I drove the truck back from VA dealership 20mpg 2 Pump chages and lota miles later 16.5 is the best I can do at fastest 65mph 2000rpms. Would like to up this with the price of fuel.

[skittle]

The only thing left out of the discussion about the affects of faster travel speed... is the simple fact that most of these vehicles are geared to run somewhere well above the optimum 1800 rpm and as you increase travel speed you also increase engine speed. Since the engine efficiency drops off quickly as engine speed increases above 1800 rpm, the faster travel speeds really hurt. A simple test would be to compare fuel economy at the same engine rpm in direct vs. overdrive. That would show you the areo and friction stuff, excluding the engine and some of the transmision. I have lots of mpg data on a stock 1995 1/2 ton 4wd 6.5 turbo with 3.42's. I couldn't tell you what the mileage is at 65 mph, I've never done that! My year around average is about 14.5 mpg. Less when towing (11 ish) and more when not towing, especially at 70-75 mph (16.5 ish). Enuf for my first post.

[More Power]

Welcome to the board!

I've long held that 1800-RPM and 65-MPH are magic numbers for best fuel economy. The engine's torque peak will appear at 1800-1900 RPM and wind resistance at 65-MPH is still manageable, yet allow you to travel at a realistic speed.

Jim

[Nobby]

Makes sense to me with 3.42's and 265's i'm in that 1800 to 2000 rev band and it feels real sweet right there. I see somewhere around 18 - 19mpg, i should point out that I do alot of long distance driving and my foot is not made out of lead. I am just installing a 4" exhaust and hoping to maybe break the 20mpg barrier. Not sure if my foot will stay unleaded tho!

To me if I had the money an underdrive with my current setup would be a sweet rig that covers all bases. If I had that kind of money a Duramax would probably make more sense tho.

cheers
Nobby

[6.5 Detroit Diesel]

There was a lot of discussion about how bigger tires cut down milage. I agree that with a typical small gasser engine, this would be the case. However, the diesel puts out so much torque that I don't feel it affects milage. I am running the 36" Military mudders combined with a 4.10 rearend and a NV4500. My truck weighs around 6300 lbs with a full tank of diesel and driver. In town my milage sucks, (15-16). On a recent trip on the highway we kept very close tabs on the fuel consumption. With around 800lbs in the box I got close to 24 mpg. (Imperial) I kept engine speed in between 1,600 and 1,800 rpms which worked out to between 60-65 mph. This is significantly better than with the stock size tires.

[TDSECK]

I just had my 4:10 ratio axle replaced with 3:42 after much reading and thought about it. I also had the factory posi replaced with an Eton unit.

Thanksgiving of 2011 I towed my old 91 Montero 4x4 to Maine on a U Haul trailer and got around 15 mpg from NJ. I didn’t go past 55 mph for the trip.
On the trip home I got 18 mpg but had to keep the speed under 60 mph as I didn’t want to go past 2000 rpm for my 6.5. It was tuff having every one pass me for the whole trip home! So it was bitter sweet, good mpg but a very slow drive.

This Sub was very well taken care of by the pervious owner. It has 1149000 miles on the clock and runs and starts well.
The only mod I can see is the FSD has been replaced and relocated in the front bumper. Also the exhaust system is 4”. I replaced the straight through type muffler with a 4” reveres flow muff to lower the noise level inside.

I am planning another trip to Maine in July and will let you know what mpg I get with the new gearing.

So far I like the 3:42 gearing MUCH better than the 4:10
I have no plans to do any heavy hauling with my Burb. I bought it for long trips and hauling big stuff inside with the 3rd seat removed. (a 4x8 sheet of dry wall or plywood fits right in!
So far:
Less engine and exhaust noise (no one talks about that)
Less engine wear per mile
Hopefully better mpg

Some one said the having 3:42 gearing makes your truck or Sub a dog! I disagree! It’s a diesel and now the rpm’s are 1200 to 1500 for everyday driving around my NJ suburbs right where it should be, in my opinion.

The Trany Shop offered to recalibrate the vehicle speed sensor buffer but I felt I could do it after reading about it in the Vol 1 Book about the 6.5.
Has any one out there done that mod them selves and or installed the 7-position dip switch instead of the jumper settings?

PS: FYI I wanted to install a overdrive unit but found out from the mfg that the “Auto” type transfer case that is in my Burb is a one piece unit and can not be split apart for the install, other wise I would have gone with the overdrive unit…
The manual transfer case will work with the overdrive unit I looked at.

[DennisG01]

VSSB re-cal... yes, have done it. I bought a DIP switch (after I did the recal) with the anticipation of soldering it in for future use but never did. Either way, it's a pretty easy-peasy thing.

[TDSECK]

Can you tell me where you bought the dip switch?
Radio Shack no longer sells the one shown in the Article written in the Turbo Diesel Vol 1 Page 51
Also I can not fig out how you translate the divide code into ones and zeros.

[greatwhite]

1998 K2500, ECLB, Auto, 4:10, 265 75 16.

Latest results are 18 MPG combined.

Combined is roughly 60% highway, 40% city. Highway speeds not above 100 Kph, windows up, AC on.

Just switched rims to a set of PY0's from a later 2500HD. Requires far less throttle for same rate of acceleration and lighter touch highway to maintain speed.

Weights:
steel wheels scaled at 34 lbs each
PY0's scaled at 17 lbs each

That's 50% savings at each wheel in rolling mass.

Hoping for a small return on the less rolling mass. Would be overjoyed with even 1 mpg increase.

[DieselDavy]

Wow!
While 68 lbs are a lot go haul down the road, I'd be surprised if you gained 1 mpg.
Keep us updated on how much you gain!

[More Power]

I've been thinking lately about the questions posed here for improving fuel economy in the 6.5.

My thinking includes a trans swap to a TH700R4 which is more efficient (higher OD and less rotational resistance) than the 4L80-E, a mechanical DB2 (possibly a 6.2L pump) and a Holset HX-35 for a more free flowing turbo.

I know that that combo in a 6.2L diesel pickup I owned in the 1990s delivered 24-25 mpg. That truck was geared 3.42, and ran a Banks Sidewinder turbo system. The 6.2L engine itself, DB2 fuel injection pump and matching injectors were all pretty fresh.

By comparison, the 1994 Blazer we have (6.5TD/4L80-E, DS4 and 3.73 gearing) has to be coaxed to produce 17 highway...

Just thinking out loud...

[2INSANE]

I've been thinking lately about the questions posed here for improving fuel economy in the 6.5.

My thinking includes a trans swap to a TH700R4 which is more efficient (higher OD and less rotational resistance) than the 4L80-E, a mechanical DB2 (possibly a 6.2L pump) and a Holset HX-35 for a more free flowing turbo.

I know that that combo in a 6.2L diesel pickup I owned in the 1990s delivered 24-25 mpg. That truck was geared 3.42, and ran a Banks Sidewinder turbo system. The 6.2L engine itself, DB2 fuel injection pump and matching injectors were all pretty fresh.

By comparison, the 1994 Blazer we have (6.5TD/4L80-E, DS4 and 3.73 gearing) has to be coaxed to produce 17 highway...

Just thinking out loud...

After doing my 700r4 swap behind the 6.5 TD Optimizer with 4.56 gears, GM1 turbo (Soon HX35w), it for sure gets better MPG in town and on Hwy compared to the Th400. Even better Mpg in town then my Stock LBZ Duramax. I have not crunched all the number yet except Hwy mountain grades where it gets about 15mpg empty at 75mph and about 10mpg towing a heavy 2200 pound pop up camper. I have not been conservative. So far 3,000 miles with the built 700r4 and it is still going strong with my heavy lead foot! That 1st low gear is amazing!

[ToddMeister]

Yeah my 1995 with a CKO-HX40W-II turbo, DS4, and 4L80-E is very similar in MPG to your 94

Most of my miles are local stop/go in town and I am averaging about 15 MPG

[More Power]

Yeah my 1995 with a CKO-HX40W-II turbo, DS4, and 4L80-E is very similar in MPG to your 94

Most of my miles are local stop/go in town and I am averaging about 15 MPG

The Blazer produces 15-16 locally as well. Doesn't make sense when compared to that GMC I owned with a Banks 6.2L. The Blazer's engine is equipped with the small port cylinder heads, which don't seem to make a lot of difference - or there are other factors that make more of a difference.

Our 6.5TD Power Project engine ran with the large port cylinder heads, 4L80-E, 4.10 gearing, GM-8 factory turbo, a mechanical DB2 marine pump and matching injectors. It would deliver about 2-mpg better than the 1994 Blazer (we owned them together in 2000).

So... it looks like the transmission and the turbo make up the rest of the difference in MPG. I do know that when I swapped in the OD equipped TH700R4 for the TH350 3-speed non-OD automatic that that 6.2L GMC diesel K1500 pickup had in it, I saw a jump in fuel economy of 5-7 mpg before the Banks system was installed. Adding the Banks Sidewinder made no difference I could measure in the 65-mph fuel economy (50 miles per day commuting speeds).

[Robyn]

Just my opinion here...

Having been into several 700R4 OR Currently called the 4L60E

The 700R is a wimpy gear box.....Even the later renditions are nothing to write home to momma about.

I have opened up several of these that were behind 6.2 diesels....Literally shook to pieces.
The clutches are tiny, the sprags are also tiny.

The planetary gear sets are small....a 5 planet upgrade helps....

The factory sun shell is a POS..."The beast" (After market unit) is much better

The input shaft is pressed into the aluminum clutch housing.
The housings break or the splines rip out.
There is a hardened steel piece the presses over the aluminum hub to help it out.

Several other issues.....
The 700R or 4L60 is OK behind the V6 and the 305 V8.....

The factory did not use the 700R / 4L60 behind the 6.5 for a good reason....The N/A 6.2 could break them....The 4L80E is a good durable box and will hold the 6.5....

The cost of doing the swap, plus all the parts that need to be massaged....Drive shafts and such....

IMHO This swap would be a really bad jump.....And I am not sure you will get much if any gains that will ever pay off before the little gear box that could ...grenades...

When the 700R goes bang....It's very ugly, and usually spreads parts all over the street.
I trashed 3 of the 700R in my K5 Blazer......Then dropped in a TH400 with a nice tight RV coverter.....No more issues

The 4L80 does have a tad more parasitic drag due to it's size....Size ....as far as bigger parts is a good thing.
The TH400 and the 4L80 share some internal parts....Bigger is better..


Ma general likely knew what they were doing....

Just sayin....