Correct gears with a 4l80?

[1968vetL-71]

I was wondering if anyone was running 35"-36" tires with a 4l80e and 3.73 gears? If so, is the OD useable or do I need to bump up to 4.10's or 4.56's to get the rpm's in the right range so it's not bogging down? I've always ran a manual trans in all my trucks so it never really mattered too much. I have a 4spd/205 vss setup I can run instead of the 4l80/205 vss combo if I'm not getting the use of OD out of the auto. Hate to waste it if its not beneficial. Any info is appreciated.
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[bilfman]

I have 32" tires in my 4l80 swap and run 3.73 gears this spins me around 1850rpm at 60. A little low for my liking but I just completely rebuilt both front and rear diffies this past spring so I'm not going to open them up just yet. I think 4.10 would be my minimum with 32" tires, money not an issue, that would be for my liking.

So for your question, with my 3.73s, 32" and od it is just fine for cruising. But when I pull the big boat I find myself needing to shift to 3rd occasionally. I am currently redoing some 781 heads with a bigger exhaust valve and roller rockers. Also switching to a stouter lower rpm cam to bump my power and torque for pulling to help 4th towing out.

So I am thinking with 35's 4.10 or 4.56 is the way to go. I had 4.56's before I had the 4l80 and wish that I had that back.

Hope that helps.

[b454rat]

Depends on what motor your running. My father used to have a 98 2500HD 454/4l80 that had a 6" lift and 35s w/3.73s in it. Truck would friggin move. I had a 97 that was stock with same motor/tranny but with 4.10s and 285s, didn't have nearly the power. But, I think it had issues just before it got sold.

If your running a small block, might want to go with at least 4.10s.

[mcmlxix]

4L80e OD ratio is .75

35" tires at 65mph and 3.73 gears = 1746 rpm
36" tires at 65mph and 3.73 gears = 1697 rpm
35" tires at 65mph and 4.10 gears = 1919 rpm
36" tires at 65mph and 4.10 gears = 1866 rpm
35" tires at 65mph and 4.56 gears = 2134 rpm
36" tires at 65mph and 4.56 gears = 2075 rpm


here is a link to the calculator I used...
http://www.csgnetwork.com/multirpmcalc.html


I have a 4L80e going in my Blazer with 4.10s and I'm looking at 35" tires that are more like 34". Check with the tire manufacturer for actual diameter...

[kwmech]

The 4.56 gearing with the 25% overdrive equates to final drive of 3.42. So 3.42 final gearing with a 35'' tall tire would be good. When I had my suburban I geared it with 4.56s and was running a 700r4. drove really nice, that was with a 285-16'' tire which was a bout 31.5'' tall. So, I would go with the 4.56s

[1968vetL-71]

Thanks for the input gentleman! I can't decide if I want to keep my auto or convert to 4spd. I have everything to do so including a 4spd tilt column with cruise!! Well see how lazy i want to be. lol. But I'm thinking a loaded 91 crew with a stick would be cool. Thanks again.
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