Technical scotts 12 bolt posi

hello i have a scotts ?473 posi detroit locker in my 56 .in my opinion way too low geared for the street the trans is a turbo 400 with manual shift 3 speeds if i change the rear end gears to 373s what effect will it have on that trans except not having to shift so soon will it just give it longer legs for speed ?

 

Longer legs, improved fuel economy and a risk you may not beat them all block to block.

 

Is the '56 in your avatar the one we're talking about? It probably weighs around 3500 ish pounds. What's your engine setup? Stock or stall converter? 3.55 or 3.73:1 gears would let the TH400 take you to 55mph at around 2300 rpm. While still getting out of the hole.

 

https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

Here's a gearing / rpm calculator.

I don't know the rest of your setup, 3.73 or 3.55 gear is good street gearing.

 

I'm a bit confused because I haven't heard of a 4.73 ratio for GM or 12 bolts. Is it a special ratio?

Pat

 

I was just thinking the same, 4.56 I think I recall and 4.88.

 

I run a 3.89 in my car with the M20, a bit wound up at 70 but has great acceleration.

 

I have never heard of 4.73's either, 4.33's yes. But I know of a group of Mopar Stock Eliminator racers that got together and had some 470-somethings made. Also, if Aircoup has a 9" there are so many used NASCAR gear sets out there, it would make your head spin at the selection! Gene.

 

hahaha thats ok

great its now 35 or heiher at 55 -60

 

327 w 350 heads a nice cam dominator manifold and a 650 holley

 

Air, with those tall tires, I'll say 3.73s
How far will you have to drive to Lloyd's?

 

yes thats the one !!

 

from what the seller told me yes its a scotts built rear center section !

 

my rear end !!

 

3.73 would put you about 3500 at 70 without o.d.

 

How did you get that rpm without factoring in a tire diameter???
You would be running a very small rear tire to get those figures.

 

26 inch tall tire. about the dia. of a n50 15 tire

 

Something bugging me and I have to say it, your rearend is just a 12 bolt. Scott's is just the guy that built it. Stop calling it a Scott's rearend, it is simply a 12 bolt Chevy rearend. Plenty of previous replies have given you info on figuring out what gear ratio you can change to. Consider what your intended driving is, and then make changes to meet that. With some cam and being a 327, a 3.73 might be a nice choice as suggested. 3.73 is a common available gear for a 12 bolt. You also need to actually open the rearend and see what exact gear ratio you have, and what series carrier it has; probably a 4 series. Depending on the carrier, you may or may not need to get a new one 3 series.

 

Nice car aircoup!

 

Ok. Yes, with a 26" tire you would be approaching 3500rpm doing 70mph with a T400.
And yes, 26" dia. is quite a small tire.

 

well thanks for the info yes 373s is what im going to do . a scotts is new to me but its what the guy that built it said it was so ...