Gearing suggestions for my LS swapped truck

[layinrocker65]

Truck has been on the road for about 7 years with the 5.3/4L80e swap. Still has the stock 12bolt with 3.08 gears. About 28.5” tire height. Looking to make the truck a better around town driver but still cruise the freeway. Will be doing some mild towing. Any gear suggestions?

[mongocanfly]

at 65 your turning around 1600rpm.....a 3.73 will give you about 2000rpm......use this rpm calculator to help figure it out.......http://www.csgnetwork.com/multirpmcalc.html

[tucsonjwt]

Having bought a lot of new Tahoes, Yukons, Silverados, and Sierras in the past 15 or so years, the 3.73 is the most common rear axle ratio for some light towing and adequate acceleration, but the 3.23 is better for fuel economy and highway cruising, IMHO. The difference in fuel economy between the two ratios will not be noticeable if you drive with a heavy foot.

[RADustin]

personally I'd get a slightly looser converter and go 3.23. 2000rpm at 70 with this setup and it'll move better off the line. The 80e is a tough transmission to get to feel sporty and have good highway manners because of the 2.48 1st gear and .75 4th VS a 60e that is 3.06 1st and .7 4th.


that or slightly looser converter, keep the 3.08 and add one or two turbos.

[Palf70Step]

3:42 is also a good combo. It's what most of the newer LS equipped trucks come with. Seems like a good mix of cruising and low end.

[RADustin]

Originally Posted by Palf70Step

3:42 is also a good combo. It's what most of the newer LS equipped trucks come with. Seems like a good mix of cruising and low end.

yep.

4L60 with a 3.42 === 4L80 with 3.23 on the interstate. only about 20 rpm off.

problem is 1st gear may feel a little heavy with a stock converter.

you'd need a 4.22 gear with a 4L80 to feel like a 3.42 4L60.

[layinrocker65]

Thanks for the opinions. I think 3.42 might be a good choice since I can keep my carrier. Should be a relatively cheap mod. I do not want to spend the money on a converter or turbos for this truck. Got enough fast vehicles. Need at least one I can always count on lol

[mongocanfly]

3.42 is not much of a change from a 3.08....my 13 gmc has 3.42s and its always downshifting....my 99 chevy has 3.73s and doesn't have the shift issue....
your 3.08s with a worn set of tires will add about 100 or so rpms at 65
3.42s will only be 183rpm increase over your 3.08s at 65...3.08=1652rpm....3.42=1835rpm
my 81 6.0 has 4.10s turning around 2100 at 65....and I love it...
bottom line its all in what you want.....

[layinrocker65]

That’s what I’m looking for is people experience. Thanks. I appreciate it. I have 3.42s on my other LS trucks but they’re turbod with loose(ish) converters so it’s so hard to tell that a stock truck motor needs. I’ve never owned a new LS powered truck.

[mongocanfly]

3.42s will def be an improvement over the 3.08s...but I would give a lot of thought to 3.73s if it were mine...especially with the od and towing....
my 81 6.0 with 4.10s gets roughly 16-17 mpg at 344hp...but so does my 13 z71 5.3 315hp with 3.42s...and so does my 99 5.3 270hp with 3.73s...
but I know some get 20+...
but mine dont

[mongocanfly]

also something else came to mind...have you ever had it on a chassis dyno?...that can make a huge difference in the performance of the LS engines....my 81 gained over 40hp on the dyno and they could have went more if I wanted....if you do change the gearing its something id recommend.....

[layinrocker65]

Originally Posted by mongocanfly

also something else came to mind...have you ever had it on a chassis dyno?...that can make a huge difference in the performance of the LS engines....my 81 gained over 40hp on the dyno and they could have went more if I wanted....if you do change the gearing its something id recommend.....

I can tune the truck but I have just been way too lazy to do it. It’s already licensed on my HP tuners. I’m not looking for performance necessarily, just know I’ll need more low end pep with towing. Will probably tune it when I do gears since I’ll be changing the setting in the pcm anyways

[D13]

My '17 K10 regular cab long bed is 3.08 with the 5.3. 22mpg and still can overpower the tires in a heartbeat. Adn drag anything I'm dumb enough to hook it up to.

[RADustin]

just curious why you put an 80e behind a stock 5.3? The gear ratios really do suck for performance.

anyone who doesn't have a 4L80e in a light truck really won't understand the problem with first gear in the 80e.

I talked to my brother for real world experience, he has 3.73 now in his c10 with a 4.8L and 4L80e. He described it as if you 'need' an 80e than you're not going to like anything else other than 4.10s. He is switching soon.

[layinrocker65]

I put an 80e in it because I had one laying around. 3.08 is just too high of gearing for a truck I drive mostly in town.