Beamin23

I have a 1972 cutlass convertible with a 455 motor low compression motor cam intake headers 750 carb 2000 stall bolt up to th350 I have 15 inch rally's I think there 255/50/15 i mite upgraded to 20 inch wheels later I want 3.23 or 3.42 I want to burn out easy and get off the line faster and still have drivable to go 5 hours trips what gears u think would be best I don't want a dog off the line ?

RetroRanger

I have 3:42s w 255-60-15s w th350 at 70 mph I'm turning 3kish rpms. Some will say that isn't screaming but if I was on a 5 hour trip I would prefer an extra gear or a lower rear end ratio.

Beamin23

What's the longs you've been on the freeway to the point is unbearable ?

Allan R

455 is a torque monster, so make sure you build your TH350 to take the pounding it sounds like you want at low end. The factory put TH400 behind the 455 to handle the power, and also suggested the 3.42:1 bears. For overall performance and highway I'd suggest possibly dropping to a 3.08:1 . Note also that you've changed to 15" wheels which is an inch taller than the factory's 14" wheel in 1972. You could likely go with the 3.23:1 gears and get the effect of closer to 3.08:1 that way.

RetroRanger

Everybody's got different tolerances, but the car could be driven cross country like that, i just prefer lower hi way rpms. I have a newer muscle car w 5 speed that turns 2 k ishrpms at 70 mph, it's less noisy Engine wise in the cabin even tho it has a louder exhaust note. This makes conversation or music more pleasant and easier . Given the choice again w no other changes I would have got a 3:08 or kept my original 2:7x rear. I don't race the car but I do drive it like one would like to drive a BBO posi car if you don't plan on an overdrive in your future, I would consider how you use the car most and accomadate that.

Allan R

^^^ True enough. A 455 could roast tires even with being married to a 2.56:1 which a lot of CS came from the factory with. I changed my SA code axle 2.72 (factory 72 Cutlass S) to posi 3.42, but I also keep the tire and wheel size stock at 26.5". Didn't change out the 350/350 combo.

Qwik71442

out of the two 3.23

joe_padavano

There is only a 6% difference between the 3.23 and 3.42 gears. You will be hard pressed to see or feel a difference. 255/50-15 tires are a Honda-sized 25" in diameter and nearly two inches smaller in diameter than the OEM tires. I'd go with 245/60 or 255/60-15 tires.

oldsmobiledave

When finalizing a gear ratio you must also consider tire diameter, intake, converter, cam profile, engine displacement, vehicle weight & how you use the car (amongst other factors).


If you can't decide between a 3.23 & a 3.42 you can always swap in a Chevy 12 bolt & run 3.31s.

wr1970

I vote 323 being as you want to go to 20 inch wheels later.If you go to a 308 that would be perfect.

oldcutlass

Rim diameter has nothing to do with gearing, tire diameter is what people need to know.

wr1970

20 inch rim and then add tire. I would think that is more that a stock 14 wheel and tire.Most like more that a 15 also.

joe_padavano

Surprisingly, it usually ISN'T.

Most 20" tires are very low profile - like 35 series. A 245/35-20 is smaller in diameter than a 245/60-15. Not only do these "rubber band" tires look like crap on a vintage musclecar, with these very short sidewalls the ride sucks and the incredibly expensive rims get destroyed on the first pothole.

sailinghudson25

3.23 if your going to put a 2004r in it someday. 3.08 if not.

oldsmobiledave

Totally disagree. If you are going to a 200R4 then nothing less than a 3.42 & 3.73 or 3.90 are much better.

GEARMAN69

3.23 is the go to on a 455 w 3 spd . Which intake BTW ? Also do you have stock advance springs in the dizzy ? it should burn out with any gear ratio honestly. My 8:1 350 will spin both back tires on my wagon with 3.08's and a stock converter

anthonyP

I agree 100%.

olds 307 and 403

You want 3.08 or 3.23 max with those short tires. What speed do you drive on the highway? I say run a 275/60R15 or 255/70R15 rear tire. Make sure your cooling system can handle sustained high rpms. A 2004R needs a 3.42 gear at minimum, with the converter locked up with a 25" tall tire 1900 rpm at 60 mph. With a normal 27 or 28" tall tire, you will be 100 to 150 rpm lower, who needs lower than 1750 rpm at 60 mph?

442fanatic

I have 3:42 behind my 455, using the stock 15" rims. Cruising at 70mph it is pulling 3ks. Have a stall torque converter, medium shift kit... Built TH350, would prefer to have a 4rth gear as well. Looked at what it would take to switch it to a manual and put a rock crusher in it. Costly after the restoration... I would like to know what the 3:08s would do...
Looked at gear vendor's over drive. Another pricey option. Enjoy it's responsiveness with the 3:42, imagine the 3:23 would be not much difference. 3:08s...

olds 307 and 403

I use the Olds Gmail RPM calculator, add 300 RPM for a non lockup torque converter.
http://tech.oldsgmail.com/axle_RPM.php

oldsmobiledave

The 'Rock crusher" you want will have less 1st gear & still have a 1:1 top gear which will result in lower acceleration performance than your current T350 with the same fuel economy.


Turning 3000 rpm at 70 mph is hurting NOTHING. Just drive it.

My442

Having fun with a 3.91......

Firewalker

http://precisionsite.com/auto-x/tools/