71Cutlass-S

Great site, lots of useful information!
I'm rebuilding a 455 olds motor (68-72 casting numbers on block), going to use after market aluminum heads, bored .030 over, roller rockers, new cam etc...
Should end up around 500hp... using rebuilt TH400 trans...
Looking for rear end gearing suggestions - I'm looking for this car to hook up decent off the line yet still be able to get on the freeway at 70mph.
I'm hearing 3:23, 3:31 or 3:42 gears is the range I want to be in with this motor having the low end torque it has..
Thoughts / Suggestions please?
Thanks!

oldsmobiledave

3.23s with a 26" tire (235 60 15).

3.42s with a 27" tire (255 60 15).

3.73s with a 28" tire (275 60 15).

507OLDS

You are correct.The 3:42 is the highest I would go with a 3-speed auto,if you plan on frequent highway driving.I am assuming you have a 71 Cutlass,so if you do,and it has the original rearend,then it is an 8.5" 10-bolt,which is a good rear to build.Your gear ratio selections are 3:08,3:23,and 3:42. The 3:31 was a ratio for the 12-bolt Chevy.

Rickman48

My nephew had the same quandry when choosing a complete 12-bolt from Strange, and ended up with 3:55.
His 455 has a stroker, and I felt it'd be better to keep the RPM's down - but now he wishes for harder acceleration.
IMO, keeping the rpm's down on the highway would contribute to longevity of the motor, and I think the 3:23's would give real decent acceleration.

Ozzie

Without 2 speed rear ends or overdrive transmissions, you will have to just make a compromise. It's hard to have the best of both worlds. Numerically lower ratios mean lower RPMs, less wear, less noise, and better fuel economy. Numerically higher ratios mean better low end acceleration and the opposite of the other stuff above. Which way you go depends on what's more important to you. If you have a true 500 HP, it won't be a slouch coming off the line no matter what you do. So far you have a lot of good suggestions.

Jimmy_B

I'm in the market for a new rear end too, but not till next Spring. Currently have a stock 2.73 10 Bolt with my 72' CS. I have the same setup as the OP and am leaning toward a 3.42 from everything I've read and heard. Richmond gears with Eaton posi.

Anyone have any guess as to what RPM one will encounter on the highway (lets say going 70mph) with the 3.42 setup?

The tire selection that was posted by oldsmobiledave is interesting to me too. I'm currently running with P225/70rs14's. Would switching to 15" rims be a more optimal setup??

Not trying to hijack the thread... so I will just hang up and listen

gearheads78

You can play around here and adjust on paper untill you find the desired numbers.
http://www.richmondgear.com/101032.html

The_Jeremiah

My cutlass with a 275 60 15, with 3.89 gears (ford 9 inch ), 3k stall converter th400 behind my 455 was around 3k on the freeway, not sure if i was going exactly 70, but i was close. but theres calculators all over the net you can use to find out numbers, i use them all the time just for fun

Also, 500hp out of a 455, be prepared to spend a little bit of cabbage my friend, not saying its not do able, just saying i spent lots of money on mine, and i would be happy if it had 460 horsepower.

What are you waiting for?! Change the gears, drop in the engine, lets see this s.o.b. !!!

jims2000lt

69 442 hrer at 3540 LBs with me in it. Runs mid 11s with 3.42 gear, 3500stall th 400, and 455 with E-Brock heads.

Cruises at 2800rpm at 65-70mph with 27inch tall M/T Drag radials.
275/60/15s. I may switch to a 3.90 if I buy a trailer next spring but probably not.

This combo has always worked well for me; drive to the track, 35miles one way, race, then drive home.

A tighter converter would help with the driving mileage.

gearheads78

275-60-15 should be 28" tall

jims2000lt

Should be but they only measure 27.5 with 30lbs on my car right now. My bad.

507OLDS

The 72 has 325/50/15 tires,3:73's,and turns 2800rpm at 65. The converter is a custom order piece from Continental.It took a few converters to get what I wanted in drivability,and performance.Chris at Continental has done the best so far.It acts fairly tight driving it to & from work,and on the open road,then has a completely different attitude when I force the pedal through the floor.I had a custom TCI,but didn't get too much time with it because I split the insides of it,but my cruising rpms were noticably higher with it.The PTC converters are also very nice.No complaints with the one I got from them.I just wanted to try what Continental had.
Just don't go picking one from the selection at Summit.Those are very vague applications,and most are intended for your typical Chevy.

I would suggest something like an 11" converter,1800-2000 stall,with the 3:42's.

Qwik71442

I would use 3.23's or the 3.42's max if you want drive it on the freeway. My 442 has a roughly 500hp 455/TH400 combo and has gone 11.88 with a 3.23 Type "O" 12 Bolt. I have 3.90's now and it is quicker but I sure miss the drivability of the 3.23's Thats my .02

71Cutlass-S

Thanks for all the feedback.
Yes, the car I'm building is a 71 Cutlass - S.
The rear end I found is out of a 68 GTO, it's a 12 bolt w/3:31's, boxed arms, rear sway bar...

copper128

I'd bolt it in as-is and see how you like the 3.31's. Should be just about right with a 455.

507OLDS

Yes,if you have the 12-bolt Chevy,with the 3:31's in it,leave them in there.Replace all the bearings & seals,and if it's not a posi,put that in too.Get it all ready before it goes under the car.

Leroy Sanders

I have an 1985 Cadillac Fleetwood delgance I swap a 455 olds big block I have a set of 24 inch wheels I want to put on I'm currently buying perfomance parts for when I tear down and go in the block I want to have no slag when I take off what gear ratio do u think is best under these condition s I still want to to ride and play with the wheels on

joe_padavano

Unless you plan to just drive on the metal rims, what matters is the TIRE diameter, not the wheel diameter. Also, what's the trans, what has been done to the engine, and how do you really plan to use the car?

Mark Kramer

I am swapping a 307 to 455 in an 1983 olds 98. should. should I change the trans.?

JohnnyBs68S

Even a smog-era 455 is going to generate a boat load more torque than that 307, so if you aren't changing it to something built to handle it (TH400), then at least it will need a proper upgrade to make it stronger.

joe_padavano

Your original trans SHOULD make it to the end of the driveway before it grenades.

oldsmobilejim

1971 cutlass rag top built a 455 keeping it gas pump friendly. Seven hundred R-4 with 2500 stall and a 1971-72 Oldsmobile 10 bolt 8.5 in. non C-clip 342 ratio rear axle and 275's. I'm loving it, running 2000 rpm's at 70 mph. Next would like to get it on a dyno tweak it and then to the track. I'm sure its going to do everything I want for a good while. And yes it is expensive to build, cause it's called a Olds. Keep us updated and good luck!!!