A Drag Racing Transmission and Gearing Overview
Transmissions that are built for drag racing are different from those designed for other motorsports and everyday use. Not only are they designed to withstand much higher stresses through extreme amounts of horsepower and torque, they’re designed with a different purpose in mind. The same can be said of rear-ends or differentials. Drag racing diffs have to handle tresses and they have to perform their job in a way similar to those installed in your grocery-getter, but they are designed to do it differently. We’ll go over the types of transmissions and what your ride needs to perform as well as possible.
Drag Racing Transmissions and Rear-Ends Need to Deliver Power Early
Your daily driver-grocery-getter car, even if it’s a high performance Camaro or Corvette, has different needs than a drag racer. Sure, you may enjoy hitting it light to light, but you also have to have smooth and controllable acceleration, decent gas mileage, and a decent engine RPM when cruising around town and on the highway. Your typical NASCAR racer has pretty similar needs-controllable acceleration (no tire spin), decent mileage (can’t hit the pits every few laps for gas), and it needs to keep the engine in the RPM-band where it’s producing max horsepower.
Your typical strip burner, heck, any drag racer, is very different. You want everything the engine produces translated to those big slicks right now, not when the engine hits max RPM. You don’t mind some tire spin right at launch, because that heats the tires up and gets them hooked up quicker once you’re out of the launch box, and gas mileage? HAH!
Older drag racing transmissions were a combination of two- and four-speed manuals. There really wasn’t enough time in the run for more and shifting is a weak point, a chance to mess up and lose, or blow your engine, so we tried to minimize the of shifts. These days some racers still use two-speed manuals, but now we’re seeing more and more guys going with automatics like ATI’s SuperGlide4. It’s an automatic, but it’s used like a manual.
As drag racers, we build our engines to produce the maximum horsepower and torque early in the torque band and then drop off pretty quickly. Guys like Jimmie Johnson and Jeff Gordon over in NASCAR have engines designed to produce more at the upper reaches of the torque band. Because we need our torque delivered to the ground quicker, we need what are known as “taller gears” or a lower ratio. Back when I was turning times at the track, we were using rear-ends with 4.11s and maybe 4.56s. Today it isn’t strange to see 5.13s and 5.38s.
Manual or Automatic?
If you’d asked me twenty or so years ago what kind of transmission I would recommend for a strip burning drag racer, I’d have probably pulled out the receipts for the transmissions I had built for me-3 speed manual clutchless from Muncie. There was just no way I’d recommend an automatic transmission for a drag racer back then. They couldn’t handle the torque and horsepower we were putting out. Another reason was that there too much torque lost in the torque converter.
However, companies like ATI have automatics out like the SuperGlide4 mentioned above that can handle almost 4,000 horsepower and that have some extra-awesome gear ratios for us drag racers. These companies have also created the lock-up converter. This is a torque converter that starts transferring full engine torque through the transmission at much lower engine RPMs than standard torque converters. This means that less of our engine’s torque at lower RPM is lost to converter slippage. Thus, we get a better launch.
I have known people at the track that have wanted manual transmissions but didn’t feel comfortable with them because they required them to pull their hand off the steering wheel to shift. I can admit, when you’re flying down the strip at 200 MPH on two rear wheels, the idea of pulling your hand off the steering wheel to shift just feels unnatural. This is one of the main advantages of an automatic transmission. You can either let it shift itself, bump shift with your knee, or use paddle shifters on the steering wheel.
Another reason you might choose a manual over an automatic also deals with ease of shifting. Most manuals have a shift patterns that requires you to move the shifter up or down and to one side or another, and then back up or down. Push up against the stops and you blow your shift and your pass. However, companies like B&M got by this problem with a type of shifter that requires you to push it forward and pull it back to shift-a ratchet shifter. This makes clean shifting with a manual much easier and more accurate and, more importantly, faster. When your pass lasts less than ten seconds, you have to do everything more quickly, even shifting gears.