Changing final gear ratio

[twizted]

We ran what you would probably consider a hobby stock car on a banked big 1/4 mile dirt track some this year. We ran 26.5" or tall 8" race tires with a basically stock 350 with holley 1850 box stock carb a 3 speed manual and stock HEI weight rule was 3400 lbs.

The final drive ratio was 6.33 and we turned the motor about 6000-6100 when we were running the high line. We would like to turn 6300-6500 next year but no more so we thought about a 6.50 and wanting to try the taller 27.5" x8" race tire.
Would that give use the extra 300 or so rpm's we are looking for or should we consider more gear? Thank you for you advice

[StreetStock57H]

For every .1 in rear end gear you go or Final drive it is equal to about 100 rpms. Going from a 6.33 to 6.50 would only be about 270 rpms more roughly, plus going to a bigger tire is going to take rpms away also. To get the extra 300-400 rpms you want, i would probably go 6.66 gear that would be roughly 330 rpms

[floppyfoot]

We run a 3/8 mile track, the turns are as long as if not longer than the straights. The rpm's have to stay up. Running a 6:50 gear with a full spool with Hoosier D35 tires, right rear 92, left rear 88, turning 7000-7200 rpm's. Was trying to figure out why he turned 7600 the last race, it was a little burnout during his victory lap.

[twizted]

Thanks for you input street stock, thats about what I was thinking.
Floppyfoot- are you running stock bottom end? if so how does it stay together? just wondering cause every engine builder I talk to says to keep stock bottom end below 6500?

[speedbuggy]

For every .1 in rear end gear you go or Final drive it is equal to about 100 rpms. Going from a 6.33 to 6.50 would only be about 270 rpms more roughly, plus going to a bigger tire is going to take rpms away also. To get the extra 300-400 rpms you want, i would probably go 6.66 gear that would be roughly 330 rpms

Isn't your math off by 100 rpm's?

[speedbuggy]

We ran what you would probably consider a hobby stock car on a banked big 1/4 mile dirt track some this year. We ran 26.5" or tall 8" race tires with a basically stock 350 with holley 1850 box stock carb a 3 speed manual and stock HEI weight rule was 3400 lbs.

The final drive ratio was 6.33 and we turned the motor about 6000-6100 when we were running the high line. We would like to turn 6300-6500 next year but no more so we thought about a 6.50 and wanting to try the taller 27.5" x8" race tire.
Would that give use the extra 300 or so rpm's we are looking for or should we consider more gear? Thank you for you advice

If you're truly running a bone-stock HEI, put a replacement module in it. Stock module not reliable above 5500 rpm, give or take...

[twizted]

The HEI has a different module that is legal and runs fine to 6100 never turned more than that on track. I think street stock did mean to say 170 instead of 270 rpm.

[Driver88]

I turned a stock bottom end 7000 for 3 seasons and never had a problem. Nobody told me I could. I just did.

[StreetStock57H]

My bad, Yeh would be 170 not 270, but I'm sure he got the theory i was going toward.