Is it worth changing gears for better MPG's???

[DA BIG ONE]

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.

[16gaSxS]

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.

[JohnC]

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]

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]

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 [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]

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?

[Warren96]

'' 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?

[moondoggie]

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)