I'm building a 57 Cadillac with a twin 3076r 390 and a 4l80e. Rear tires are 29.8in tall. It will weigh around 5000lbs.

Since those specs are pretty close to a full size truck I thought this would be a good place to ask.

I would like to run a 3.50 rear gear to keep cruise rpm down. Also plan on running a rather tight converter. Is it going to feel like a pig in 1st gear?

Other options are more rear gear (which screws up the cruise rpm) or lower 1st gear in trans.

Any opinions welcomed.

 

If your Turbos spool and come on strong down low,, no its gonna be amazing..

Now they do make a lower first gear set for the 80E but its not that big of a difference in numbers..

 

I think it takes 1st from a 2.48 to a 2.75 and 2nd from 1.48 to 1.57.

 

The 3.50 gears should be just right

 

Now that i look at the tire size,, thats gonna be some good gearing..
most guys run 3.42s and 3.73s with a 28 or 29" tire.. so your right there in with the pack

 

Hey Nonnie a tranny guy told me those gears were only avail for earlier model 4L80s? Is that true? To the OP I'm thinkin not a super tight converter and it looks good to me.

 

Mines 5200lb, 370ci, single 76mm, 80e, with 373 gears with a 31.5" tire, so yours should be similar to mine. You'll be fine.

 

Thanks for the input guys, it's going together with 3.50's.

 

Man i have no clue. I just read that some of the old RVs woth the 454/4l80 come woth the diff gear sets. And i knew a company made them now or some jibberish.
Just thought id throw that out there for the OP to think bout.
But i read that they arent near as strong as the factory .48 gears.

What stall are you running in the car?

 

Thats pretty much what I heard too.