Have a 70 Cutlass Supreme and I'm thinking of changing it from a TH400 with 3.42 Posi rear to a 5 speed with a 3.91 rear. The motor is a 455 with approx. 400hp and 500tq. Looking for something that still accelerates very quickly but yet still driveable on the highway at 65-70mph. Maybe I'm dreaming but I hope it's possible. Any clues or tips on where to look for what I need is greatly appreciated. The car is a summer driver that may see a few passes a year down the 1/4 mile along with occasional highway driving. Hoping to keep highway RPM'S under 2500@70mph. Thanks

 

Look into a 2004R swap, this has been covered many times. A modern overdrive is the best of both worlds, better off the line acceleration and lower cruise rpm. Depending on how stout the engine is a overdrive might need some internal upgrades.

 

Manual transmission good.

More Smiles per Gallon.

I'd go for it, if you've got the time and the bucks.

- Eric

 

Others on line would know more about this but you may need to have your crank drilled for a pilot bushing.

My vote for any hot rod is always for the manual. My Delmont has a TH400 and now that I'm falling for the car (my original intent was to build a custom and sell it to beef up the retirement fund) and will keep it a while I'm sorry that I didn't install a manual. Even my wife, who will drive the car pretty hard when it's finished, prefers a manual.

 

I have a 5-speed swapped in behind my 350. Not 100% done yet but it's driveable and lots of fun. Then again, I absolutely hate automatic transmissions.

 

I think you know my answer! See my video link.

 

I'll add my vote for the 5-speed. Installing a Tremec in my 48 behind a 455. "Real Hot rods" Have three pedals" Is the common saying

 

 

LOL.

- Eric

 

z11375ss Nice ride! Cant wait to finish mine. The only thing holding me back right now is the cash for the 5 speed.
Mr Nick, I couldnt agree more! lol

 

I ordered a Keisler TKO 5 speed for the Cutlass. I expect it will be here around the end of jan. I think I may do Power Tour this year because it has a .64 overdrive. Yes! Downside? $3700 complete, not cheap, but what is these days! Thanks for the props Steeb75! You'll get there sooner than you think. Then you'll be like me. Ok, what do I do to it now?

 

This is a decision only you can make. I'll take a manual trans any day, but you may or may not prefer driving one. You might not need to change the rear gears, depending on the trans you pick. For example, if you get a trans with a steep first gear and a fairly high numeric OD, your 3.42 will be fine. It's all about the equivalent ratio in each gear. Just build a simply spreadsheet and do the math. You can quickly compare different gearsets with your current or planned rear ratios and pick the best for your situation.

 

I did the 2004r Thing always had an auto i absolutly hated it could never get the shift right,got alot of money tied up in it.Ordered a new Tremec Tko 600 alot of money but i cant wait,best of all my wife wants it as bad as i do 2004r going to get a new home as soon as i can collect some more parts.

 

Unintended benefit of driving a manual trans....It's difficult to talk on the phone. So I just don't answer it...lol

 

Best argument yet...I'm in!