4.10 gears are too stiff for cruising....about 3000 rpm's to do 55. You will shorten your engine life and not enjoy the ride.....3.55 is probably a good ratio to use "Ask your Doctor if 4.10's are right for you".......if I never hear that commercial phrase again ......................
VettenGoat: In my opinion, especially with a 421, I would get a "year correct" rear end for your car and run a 3.23 gear or a 3.36 gear. A 3.55 gear with a 421 would sure be great around town, but you'll be wound out on the freeway, looking at shorter engine life, higher engine temps, more road noise, and less fuel economy. The 421 has enough torque to run a really long legged gear like a 2.93 or a 3.08 and still not be able to hook up! I would suggest going for a ride or driving a 3.73 or 3.55 geared car and see how you like it. With me, it was great when I was 19, but now, I like to get in the car and GO SOMEWHERE!!! As for 5.13 gears, Yeah, I saw a guy in a white '67 Camaro one day waaay back when pull the front wheels up about 18 inches out af a stoplight on San Leandro Blvd. Needless to say, I didn't even race THAT Chevy!!!!
Jeff
The size of the engine won`t change the RPMs. I have 3.55`s with a 4-speed and it goes down the interstate with ease. I even raced a Bemmer looking thing up to about 125 and it was still pulling away strong. I drive the car all over the state and it cruzz`s awesome down the highway. A lower # ratio would get better millage, but who drives their classic GTO for gas millage??
You're right about the RPM's, Rukee. But a 421 rev's lower than a 389, and makes more power at lower RPM's. While a 3.55 is the standard gear for a 389 equipped stickshift 3400 pound GTO, the usual gearset for a big Pontiac with a 421 and stickshift seems to be 3.42 or 3.36. 3.55 was considered the best "all-around gear" in the GTO back then....... Like you, I had 3.90's out back until I went as long legged as I could: 3.36's. I have no regrets!!!!!!
The size of the engine won`t change the RPMs. I have 3.55`s with a 4-speed and it goes down the interstate with ease. I even raced a Bemmer looking thing up to about 125 and it was still pulling away strong. I drive the car all over the state and it cruzz`s awesome down the highway. A lower # ratio would get better millage, but who drives their classic GTO for gas millage??
I'm trying to figure out this gear ratio thing, Rukee. If I am going 70 mph on the highway, my 400 cubic inch engine is at about 3200 RPMs. Is that similar to your story above and, if you can venture a guess, what kind of gears am I running?
I'm trying to figure out this gear ratio thing, Rukee. If I am going 70 mph on the highway, my 400 cubic inch engine is at about 3200 RPMs. Is that similar to your story above and, if you can venture a guess, what kind of gears am I running?
Pull the diff cover and count the teeth on the ring and pinion, then divide the # of ring teeth by the number of pinion teeth.
Another way is by using Rukee's method and turn the tire 10 times and if the drive shaft turns 39 times the ratio would be a 3.90.
10 tire revolutions is too many, between counting the tire and the driveshaft it` too easy to lose count.
That`s what the ratio is though, how many times the driveshaft turns for evey one complete turn of the tires.
10 tire revolutions is too many, between counting the tire and the driveshaft it` too easy to lose count.
That`s what the ratio is though, how many times the driveshaft turns for evey one complete turn of the tires.
Thanks guys, I've been having the same inner dilemma. The 65 originally had 3:90s like Rukees, but they are long gone several owners ago and now it has a wrong 1971 rear in it with 3:23s. So I am still looking for a 65 rear and thinking about what ratio to use with the 421. Geetoguy is right, we're not kids anymore and gas isn't .35 a gallon so 3:90s are out. I'm tossing up whether to go 3:55s or 3;73s. Anyone running 3:73s? Thoughts?
Mike
The 3:55s should work well with a 421. they made a lot of torque
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