68 Gto gear swap
 

Hello everyone, I have a 68 gto with a rebuilt ys code 400 in it. The engine has pretty much everything stock (including compression) exept for the cam and rocker arms. It has 1.52 roller rockers with a Crower 60242 cam. The duration of the cam at .050" lift is 221/229 (INT/EXH). The car also has a Th400 tranny with a 500 higher than stock stall speed 12" converter. The car is running a 2.93 open rear end on 225/70/R14 tires and was planning on getting a gear swap and a posi. The car is only driven on the streets in my local area, car is never on the highway. The highest speed limit is 50 mph. I was wondering if I should get 3.55, 3.90, 4.11 or 4.33 gears. im looking for max acceleration, The car right now is a dog off the line and has traction problems since its an open rear end.

I have a couple sets of 68 dated 4:33 gears, also a 65 or 66 dated set if you want one - all in beautiful condition.

In case I do go with 4.33's how much ?

If you plan on keeping your present engine combo and don't want to make it a garage queen, 355's would be the most gear I would consider. For a long time I ran 3.90's in my 68, but that was with a RA4 style cam.Interstate or highway driving was annoying with 26" tall tires and high RPM's. I now have 3.42's with a smaller cam and the car is a pleasure to drive once again. 3.55's will get your 68 accellerating alot better than those 2.93's

I agree, with a TH400 the most I'd go is 3.55. In the chance you do take it on the freeway you'd hate those 4.33s.

Just going from a 2.93 to a 3.55 will make you feel like Superman...;)

I had 4:10s on my 1968 and it was fun for a little while but got tiring after driving the car beyond city blocks. I swapped-in 3:55s and couldn't be happier.

Based on the online calculators im going a little over 2000 rpms with 2.93s, almost 2500 rpms with 3.55s, and a little over 2700 rpms with 3.90 with my tire height and tranny at 55 mph. My jeep patriot does about 3400rpms at 70 on the freeway so 3.90s I guess isn't so bad since most of my streets in town have a 35-45 speed limit. Besides 3.90s are lower than 3.55s so wouldn't it give me have a little better acceleration and more push to the seat? but everyone seems to be recommending 3.55s

I'm running about 3k around 65mph with 3.55s, a TH400 and 225/70/R14s.

3.55s are generally a good compromise for performance and streetability, that's why everyone recommends them.

I think it's because most of the posters have "been-there-done-that" myself included. You certainly can put 3:90s in your ride and be as happy as Bill Clinton at an ass grabbing contest.

At 55 mph 2500 rpm doesn't sound bad but if you want to drive the speed limit (it's 65 in CA) then your spinning 3300 (though most drive closer to 70 mph and now you're almost at 3600). It may or may not be a problem and if you are just running the car around town then sure, 3:90s will give you a bit more push.

IMO, 3:55 are the best all around gearset for futzing around town and tolerable highway rpms. Just my 2¢

Your Patriot has half the cylinders and half the power. It needs 3.90's just to get moving.

You've got a Pontiac V8 with torque - you don't need the same gearing as a 4 banger...;)

Like I posted earlier, going from a 2.93 rear to a 3.55 will make you feel like Superman.

With those skinny 225/70/14's, you probably would have extreme traction problems with 3.90's or higher.

I've got a 3.42 geared 12 bolt in my GTO with 27" tall tires, and very happy with the "push to the seat". But I do have a 455...;)