Auto Racing: Outlaw Modified Dirt Track Car, dirt track car, peak horsepower

Question
I am racing on 1/2 mile and 1/4 dirt tracks here in Texas and I am wanting to know how to figure out the proper rear end gear ratio to keep my engine in its power band at the end of the start away with out running it flat. Right now I am running a SBC 383, a Bert Trans, and 9" with 5.67 for 1/2 and 6.0 for 1/4 mile tracks. Do you have any recommendations on this? Thank you for the help, Dave


Answer
Hi Dave:

The basics of gearing are simply to gear the car so that it exceeds the peak horsepower RPM by about 500 AT the shut down or braking point on the longest straight. It's a trial and error thing.  You'll need to take a bunch of gears with you and find which one gives those results at each track.  What this hopefully does is give you a building amount of horsepower as you accelerate down the straight, that just barely starts to fall off as you arrive at the braking point.  If you find that the car is slow off, it may be you are running a bit too much cam duration, or the carbs are a little fat.


If you're running a passenger car rear end, you really need to cough up the bucks for a quick-change unit from Frankland or one of the others.  The off season is coming, it would be a good time to start looking around.  With a quick-change unit you can try one gearset for practice, another in qualifying, another in the heats, and with luck,  have the right one for the C main .

I wish I could tell you there were a scientifuc approach to this, and there may be , but I don't know of it !


Good luck,

Dan Liddy
Sarasota, Florida