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Author Topic:   Gearing
rickbraley
Dirt Full Roller

Total posts: 58
posted November 11, 2004 02:13 PM  
What is the proper method for selecting the gear ratio for the rear end in terms of maximum RPM and matching the gearing to my engine's power band?

I recently ran my modified on a chassis dyno and based on the HP & Torgue curves it doesn't seem logical to set the gearing to turn RPMs above the level where my engine output falls off? I have been gearing the car to turn a max of around 7400 RPM on whatever track I run but my power curves show a significant decrease in power at this level. Am I just wrapping the motor tighter than it needs to be or what?

Any insight on this will be appreciated.

rrrrick
Dirt Maniac

Total posts: 192
posted November 11, 2004 04:33 PM  
I always felt that torque gets you off the corner.. and HP gets you down the straightaways. I would like a gear that is best torque RPM coming through the turn, and peaking my HP just near the end of the straight.


FASTLAP
Dirt Maniac

Total posts: 171
posted November 11, 2004 05:25 PM  
I agree. I had a 406 built once and the engine guy told me there was no need to turn it over 6000 'cause that's where the bulk of hp and torque came in at. So I geared it accordingly. Turned 5850 - 5900. Won races that way and the engine lasted 3 seasons with nothing more than rings and bearings over the off season! He still builds them that way, and they're still winning. I think there's a calculator in the tool box that would help you select the gear for the rev's you want to turn, isn't there? No sense of screamin the motor if you don't have to. Sorry a little lengthy.

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted November 12, 2004 06:34 AM  
I would shoot for having he rpms at peak HP just past the flagstand, which will end up maybe 400-500 over by the time you lift. At the same time find a gear that will work with your torque curve to get you off the corner and keep up with the other cars. I would concentrate on coming off first. sometimes in order to get a car off the corner you end up turning it tighter at the end than what you need to but if you cant get off the corner you most likely wont be able to make it up down the straight. Just my opinion anyways....

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