Boxing is often called the sweet science of sports, but when it comes to road racing, the sweet science definitely becomes running the car through the gears without tearing anything up. Circle trackers are known to be hard on their transmissions, but at most tracks once the car is up to speed it stays in one gear--nothing close to the sort of torture a hard-charging road racer puts to his gearset.
For a better understanding on what it takes to get the power from the engine to the wheels in a road- racing environment, we went to Jerico Performance Products, one of the leading manufacturers of transmissions for any type of racing. Jerry Hemmingson, Jerico's owner and founder, is a longtime drag racer, and his first trans- mission designs were for the strip. But drag racing demands easy shifting without requiring constant use of the clutch--always a plus whenever you're trying to go fast--and his designs quickly found their way into other disciplines, including road racing.
Going to the Dogs
The major difference between a dedicated racing transmission and a stocker is the engagement mechanism, commonly referred to as "dogs." Dogs are basically no more than cogs on a slider. The shifter pushes them into a receiver ring which engages the gear it is attached to. There is a separate dog and receiver for each gear in the transmission. On a racing transmission, there is a lot of "slop" (the gaps in the receiver are a lot larger than the teeth on the dog), which makes it easier to move into and out of the gears at higher rpms without fully engaging the clutch. Just like a full-blown race car, a racing transmission would be a nightmare around town but is a dream come true on the track.
"The dog-ring stuff is much faster and easier to shift at higher rpms," Hemmingson explains. "You can't shift the normal stock transmission without using the clutch. The dog mechanism that shifts a racing transmission is just a face-tooth engagement, while a stock transmission has splines that engage each other on the internal part of the slider. If you miss a gear, it burrs up that spline, then the slider won't slide on the hub, and it locks it up so that you are really stuck. On a face-tooth system, if you miss a gear for whatever reason--maybe you fell asleep or something--it doesn't affect the thing from continuing to shift because it doesn't affect the spline it slides on."
The difference between a road-racing specimen and its circle track cousin is much more subtle. Jerico's Winston Cup customers usually run the same type of unit they use on ovals with the notable addition of an integral oil pump. The pump routes the transmission fluid through a cooler to dissipate the extra heat generated by constant shifting and is powered by the main shaft running throught the transmission. The only other notable difference is gearing. In some situations, road racers limited to a four-speed transmission will sacrifice a true low gear for first in order to get tighter spacing in the higher gears.
How to Drive It
Just because you can shift a racing transmission without using the clutch, that doesn't mean you have to. "Some people shift with the clutch, some people shift without," Hemmingson explains. "There is no best way; they just do whatever works best for them. People that drive right foot gas, left foot brake usually find that it works better for them not to use the clutch. Then there are other people that drive heel/toe and use the clutch, but there is no set rule because people are better at different things.
"All you've got to do, basically, is burp the throttle. If it isn't loaded really hard, you can pull it right out of gear, and it will go right into the next gear--if it's done quickly. In a situation like going down into a turn, burping the throttle just unloads the torque on the transmission slightly, which allows the transmission to align itself with the higher rpm of the next lower gear, and it will go right in."
Remembering to burp the throttle is key when gearing down without using the clutch. If you really want to, you can force the engine without tickling the throttle, but the end result more likely will be bent linkages and driver-induced mechanical failure.
Make It Last
The extra demands placed on a transmission during a road race require some special precautions. Hemmingson recommends using a high-quality synthetic oil that can withstand the extra heat generated by constant shifting. An oil cooler also is a wise choice. In addition, keep an eye out for external heat sources that can radiate to the transmission. If your exhaust headers run too close, install some type of insulation--around the headers, not the transmission, because you don't want to trap the heat that will be generated inside the unit.
Another critical area is shifter location and quality. Again, it all comes down to the extra workout the unit gets when racing on a multi-turn course. "Shifter alignment is important," Hemmingson says. "It's usually important to use a higher-quality shifter on a road course. Ideally, you should move the shifter back as far as you can and have a straight, vertical shift stick on it. If you can't do that, then try to have it as straight as possible. If you have a shifter that is positioned forward of the driver, and the stick bends back to reach the driver, that tends to twist the shifter. Then your shifter will wear out, and you will miss shifts because of it. If you move the shifter back and straight up, it will be a lot easier on both the shifter and the transmission."
