Automotive Specialists' Jeff...
Automotive Specialists' Jeff Dorton makes a carburetor tuning change to this USAR Pro Cup car during a practice session while a crewmember also works on the suspension.
No matter if you are racing a four-cylinder in a Mini-Stock class or a no-holds-barred, alcohol-burning V-8 Super Late Model, all stock car racing engines work on the same principles. And one of the most critical is that it's up to your carburetor to provide the proper mixture of air and atomized fuel to maximize power.
When your engine builder handed over your race engine, it was optimized to the absolute best performance under a given set of conditions. Of course, those conditions are always what's found in the dyno room that day. But at the racetrack there's no way to control temperature, humidity, altitude, barometric pressure, and a host of other things. If those conditions don't match those on the day your engine was tuned on the dyno, you may be down on power.
This is why being able to properly tune your race engine at the track is so critical. NASCAR Sprint Cup teams keep a person on staff to handle the tuning duties, but most of us simply can't afford that luxury. Dedicated engine builders will often spend their weekends visiting different racetracks to support their customers, but what happens if your builder isn't at the track that day? Then it's up to you to make sure your engine is at least close to peak power.
To find out more, we spent a Saturday shadowing Keith and Jeff Dorton of race engine builder Automotive Specialists at a USAR Pro Cup race. As the owner of Automotive Specialists, Keith Dorton has built the engines powering multiple champions in the Pro Cup Series, and he regularly follows the series to support his customers at the racetrack. The track-tuning practices he's developed are certainly proven to work, and he was willing to share them with us. And as long as you're racing a carbureted engine, the same principles should work for you.
No matter if you call it practice or hot laps, before you hit the track for the first time there are a few things that should always be done. Some can be taken care of before you leave your shop if you prefer, but a few should always be done just before you leave the pits.
Keith Dorton, owner of Automotive...
Keith Dorton, owner of Automotive Specialists, reminds racers not to get too caught up in spending practice time chasing small carburetor changes. As long as the engine isn't down on power, the best way to whittle down your lap times is by perfecting your suspension setup.
"The first thing to be done is just to make a visual inspection of the car," Dorton says. "Make sure nothing looks wrong. Check the belts to make sure the tension is good and there isn't excessive wear. You should also look over the plug wires to make sure they haven't been touching the headers and have spots that are melted. Plug wires can take a lot of heat, but if you see spots where the insulation is melted or turned black from touching the headers, you should probably go ahead and consider changing it."
Next, fire the engine up and check the timing. Check both the timing at idle speed and at race rpm. If you're running a mechanical advance, make sure the mechanism advances the timing consistently when you rev the motor. If you have the advance locked out, make sure the timing doesn't change as you rev the motor.
During practice, Dorton says he generally tries to stay out of the way. And he cautions car owners not to waste too much of their practice time experimenting with different carburetor settings. Instead, concentrate on the areas that have the potential to give you the biggest speed gains. "You're going to get a lot more out of a sway bar change than you will a jet change," he explains.