AboutDan Liddy Expertise Anything concerning race cars, 20 years competition experience, Senior
Competition Driver Instructor , car builder, mechanic, welding,
fabrication, tuning , engine modifications, set up, suspension design.
Specializing in Datsun/Nissan products. Please submit questions about RACE CARS ONLY. No street cars, no video game scenarios Thank you.
Experience I have been racing for 20 years, I have been the Central Florida SCCA Regional Championship points for 5 years running, and won the championship in my class 2 times. During my first start in the 60's I won many solo awards and the State Championship Drags. I serve as a senior instructor for SCCA, and have taught in Mercedes AMG events at Daytona, and Dodge Viper Days at Sebring International. I have been in the thick of the competition for all of my career. At one time or another I have driven race cars at speeds nearing 195 MPH. It's quite a ride !
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 !
