Hello, i have a 67 chevelle with a 350 and an m-21 4spd. I blew up my 10 bolt which i believe was geared 3.08. i now have a 12 bolt under it, but it has like 5 series gears (SOOOO not streetable!) I purchased a yukon 3 series posi carrier and a 3.73 ring and pinion. My question is: for a street/strip application with what tranny i have, is this a good combo? Will I be quick off the corner and still have somewhat decent highway driving? thanks guys-John

An m-21 is 1:1 in 4th gear, just like a TH 350. I had 1:1 with 373's, and my engine ran at about 3000 Rpm going about 65. This was a little fast for me, but the 350 didnt seem to care. It definitely used more gas than if I had something less.

try this
http://wahiduddin.net/calc/calc_speed_rpm.htm
dave

I wish I had stayed with the 3.31's. The 3.73's use way to much gas and the extra rpms make my 454 way to loud.

so basically they're not so good for the highway, but i'll get a faster shot out the whole? thanks again guys-john

John,

I have seen a bunch of posts on this issue and the common response is 3.42's. I had the same problem (12 bolt w/4.56 gears). I decided on a new 3 series posi and 3.42 gears for my '66. It seems to be a good happy medium gear for performance and driveability. If you want another great RPM calculator, check this out:

http://www.f-body.org/gears/

It lets you enter your tire size and calculates the diameter for you.

Vince

John (Or anyone):

If you have Microsoft Excel, I can send you a spreadsheet I made that lets you pick a transmission, tire size, gear ratio and then see a large chart of RPMs in each gear and the corresponding MPH. PM me if interested.

John (Or anyone):

If you have Microsoft Excel, I can send you a spreadsheet I made that lets you pick a transmission, tire size, gear ratio and then see a large chart of RPMs in each gear and the corresponding MPH. PM me if interested.

Showoff...

Pm sent.

Showoff...


Who you calling a show-off? :boxing:

:D

Hope you find the sheet useful...

Who you calling a show-off? :boxing:

:D

Hope you find the sheet useful...

I was afraid to open it, thought you would send me a virus after what I said. :D This thing is awesome. Nice work. :thumbsup:

so basically they're not so good for the highway, but i'll get a faster shot out the whole? thanks again guys-john

The 3.73 might make it feel faster out of the whole,but it doesn't mean that it will be faster!

You sure you had an M21 with 3.08s? It would have been terrible to drive anywhere where there was traffic. I have found 3.50 and a fairly tall tire is about all the gear I want for a street car.