Changing rear gear ratio

jorgejohnson72 · July 29, 2021

i have a 4.3 vortex v6 in a single cab with 4.11 gears. it cruises comfortably at 50 but am really looking for 70mph cruising at about 1,000-1,200 rpm. What gear ratio should i put? and any tips for doing the swap?

Grumpy Bear · July 29, 2021

I had to make some assumptions based on your photo and little detail. It matters not. Ya just can't get there from here.

IF the transmission is a 6L80 the high gear is 0.67 and a 2.73 gear running a 245/70R17 (681 revs per mile) then 70 mph is 1450 rpm and a stone pig.

CamGTP · July 30, 2021

In 2013 they still ran the 4L60e with the 4.3 engine.

Did someone install 4.10's before you or something??

I'm not exactly up on my 4.3 option knowledge but I didn't think they ever had those gears, just 3.42's or 3.73's.

If you want better cruising RPM, you'll need to go down to 3.42's or 3.73's if it really does have 4.10's in it. I'd even do 3.55's if they offered those for the rear. Do the gear swap, get a engine/transmission calibration/tune fixed and away you go.

Edited July 30, 2021 by CamGTP

Grumpy Bear · July 30, 2021

33 minutes ago, CamGTP said:

In 2013 they still ran the 4L60e with the 4.3 engine.

Did someone install 4.10's before you or something??

I'm not exactly up on my 4.3 option knowledge but I didn't think they ever had those gears, just 3.42's or 3.73's.

If you want better cruising RPM, you'll need to go down to 3.42's or 3.73's if it really does have 4.10's in it. I'd even do 3.55's if they offered those for the rear. Do the gear swap, get a engine/transmission calibration/tune fixed and away you go.

Okay that is useful. That transmission has a 0.696 high gear.

Same as before but 3.42, 245/70R17 and 70 mph, 4L60E 1892 rpm.

Same as before but 3.73 245/70R17 and 70 mph, 4L60E 2064 rpm.

4.10 gear yields 2268 rpm

There is no 3.55 option for the 10 bolt 8.625 diff.

jorgejohnson72 · July 30, 2021

22 hours ago, Grumpy Bear said:

I had to make some assumptions based on your photo and little detail. It matters not. Ya just can't get there from here.

IF the transmission is a 6L80 the high gear is 0.67 and a 2.73 gear running a 245/70R17 (681 revs per mile) then 70 mph is 1450 rpm and a stone pig.

the tire is 265/65/r18 with a 4L60E so i had made the assumption from how short the gears are that they had 4.11 gears but turns out my truck has 3.23 but i still want longer gears.

jorgejohnson72 · July 30, 2021

sorry it actually has 3.23 but it still feels short . what is the next step longer that chevy sent with these trucks?

Edited July 30, 2021 by jorgejohnson72

CamGTP · July 30, 2021

Did you put different wheels on it too?

Most single cab work trucks like that come with 17's.

There is nothing else offered. They had 3.23's, 3.42's or 3.73's in the half tons like that with a 4 speed auto.

I just don't see a way that you will ever get to 1,100-1,200rpm at 70mph with your truck. It will ruin how it drives in all the other gears. If you go to a different tire size that could lower the rpm, but anything under 1,400-1,500 in a 4 speed is going to be really tough.

My 6 speed does 1,700ish rpm at 70mph with 265/65/18 tires and I can get low 20's for fuel mileage.

Grumpy Bear · July 31, 2021

5 hours ago, jorgejohnson72 said:

sorry it actually has 3.23 but it still feels short . what is the next step longer that chevy sent with these trucks?

Still under 1800 rpm. You're basing this wish on how it feels at 50 mph (your first post) but it takes a good deal more power (torque) to run 70 mph than 50 mph. Hold up a sheet of plywood in a 20 mph wind.

3.08 gears are available but not factory 'flash'. Will take an aftermarket device. All that will buy you under 100 rpm. At lower speeds the trans will start hunting like a dog in a field full of rabbits. Every bump in the wind, undulation in the road will run it from high gear locked up to 3rd gear unlocked. I will drive you batty. But it is possible if but costly.

I had a 76 Caprice 350 TBI wagon geared 3.08 with a TH700R-4 just wore itself out several times rifling through the gears and never could get happy. That had much shorter tires. Just say' n.

TxVet33 · July 31, 2021

So GB ur sAying even withBlackBear the shift points will hunt??? I’m seriously considering BB tune dang it. We talked about V4. To V8 and the 6spd getting to high gear ASAP. But u didn’t mention hunting tranny????

Grumpy Bear · July 31, 2021

1 minute ago, TxVet33 said:

So GB ur sAying even withBlackBear the shift points will hunt??? I’m seriously considering BB tune dang it. We talked about V4. To V8 and the 6spd getting to high gear ASAP. But u didn’t mention hunting tranny????

He has a Vortec 4.3. About 100 less hp than the Ecotec 3. How much torque do you think a 190 hp motor has at 1800 rpm? If it doesn't kick back, forced by a tune, it WILL tear itself up lugging.

Ya just can't wish a thing into existence and another thing out of it.

TxVet33 · July 31, 2021

yup, I wish I could find the end of the rainbow. I worked on Army helicopters most of my adult life.... In the air you fly through the rainbows, dad-gummit...

Sharpz · July 31, 2021

sounds like buying a 1/2 ton short body w/ 5.3 is the cheaper way to go. Sell yours and put toward the other. If you start changing gear ratios it defeats the point of a gas saving truck and without adequate power. There will be someone very pleased with what your stock 6 offers them.

Cruising at 80 mph in Oklahoma (no hills) my z71 extended cab, w/ 5.3 (265 70 r 17) will be happy about 2200-2300 rpm, w/ a 10 foot job trailer. 65-70 just about 1800-1900. I bet the single cab empty will do even better.