71cutlass350

Hi Im trying to figure out what would be the best gears for my setup. I have a 350/350 that's mostly stock except for the intake and carb. I pretty sure that I have 2.73 gears right now but I have to check and make sure. I want to get more acceleration off the line but still maintain to have decent highway driving. My rear tires are P255/60R15. Thanks

z11375ss

I would go with the 3.08s myself. Even though I have 3.73s in my Cutlass. I have a 5 speed manual though.

Octania

I'd vote for 3.42
Note that the dividing line between "performance" and "economy" is between those ratios- the axles and other parts for the 3.42 may be harder to find and pricier because the 3.73 and 3.90 owners are also looking for those.

joe_padavano

The difference in RPM between the two will be about 11%. Assuming 26.5" diameter tires, that's 2360 RPM at 60 MPH vs. 2600 RPM. Get the 3.42s.

My preferred solution is 4.33s and a 200-4R, by the way. 2240 RPM at 60 MPH in fourth (and a hell of a launch off the line).

yankees

27 inch tall tire then go 3.42. True ratio could be around 3.32 with 27 inch tires. 26.4 diameter is supposedly for the true gear ratio and for every inch the ratio changes by .1

jdana24

I had 3.08 with a 310hp prior to my rebuild, with a Muncie M21. Now I have 348hp and switched to 3.42, and am glad I did. My tires before and after the rebuild are P235/60R14. Highway driving at 55-60mph is not a problem with the 3.42's. I would suggest the 3.42 if you want to have some acceleration on the line. JMO.

oldsmobiledave

Why are you choosing between 3.08s & 3.42s when 3.23s are available & the perfect compromise gear?

71cutlass350

Thanks for all the advice!
And the 3.23 are a good compromise but I want to buy some used and I can't find to many of those.

joe_padavano

The TRUE ratio will always be 3.42:1 until you change the gears. The EFFECTIVE ratio will depend on the tire diameter, and this only applies when comparing two different tire sizes. The difference is purely the ratio of the diameters. Going from 26.4" diameter to 27" diameter is a 2.27% change in EFFECTIVE ratio, or the equivalent of 3.34:1 gears with the original tires. You'll never feel that small a difference.

Of course, that also means that you would have had 225/70-14s before and need to change to 255/60-15s to get that diameter difference.

charlie_hustle

I am considering basically the same upgrade as the original poster. I have a 350/350 combo with 2.73. there is a 3.08 open rear end for sale locally and the price is right. however, is such a small (~13%) bump in ratio worth the bother?

i'd love to upgrade to a 2004r in the future, as well. would it be smarter to just do the trans swap first (deeper 1st AND overdrive), rather than an incremental change in differential ratio? the goal for me is to maintain comfortable highway cruising and make the car less of a dog off the line. I am just looking for some totally subjective advice from anybody who has tackled this already on a low compression small block (1972).

drop top olds

I would jump on the bandwagon of 3.42 gears for the original poster. That is what I am going to upgrade to when I can.

For Charlie-Hustle, I would only change to the gear seat I wanted, not use an interim that is not much different than what you have now.

Joe has a good idea on the 200 4R and lower gears also.

Allan R

I had 2.73 open in my car till last year. 225/70/14 on all 4 corners. My plan was for 3.23's but went with 3.42's instead. Same thing as you guys 350/350 stock. There's no shortage of suppliers for any of these gears BTW.

If you find that 3.42's are too short for the majority of your driving, you can always change the tranny to a 200 4R to balance performance and some degree of economy as it's over drive ratio is .67:1. It will bolt right up to the 350 no problem and shouldn't lug at all with 3.42's. Just a thought.