Drag racing is a game of seconds—even tenths and thousandths of a second—where the racer is trying every trick possible to shave off tiny bits of time from their elapsed time, or e.t. Some changes knock off a little time, others knock off chunks, but getting the quickest e.t. possible is always an activity done in stages rather than all at once. One way to knock a sizable chunk off your e.t. is to replace your stock converter with one geared more towards quick launches. After all, a stock torque converter is set up more for smooth street manners and gas mileage than low 60-foot times.
A converter lowers e.t.’s by raising the stall speed, which allows the engine to get into its torque band quicker (closer to peak torque) and achieve lock up. For example, if you have an engine that has a peak torque range of 3,000 rpm and a peak horsepower range of 5,500 rpm and you put a 2,000-stall converter in the vehicle, then the engine has to climb from 2,000 rpm to 3,000 rpm before it really starts to perform. With the same combination but install a 3,000-stall converter instead you have drastically reduced the amount of time it takes to reach peak torque, where the engine’s torque and horsepower are created. The higher stall speed also creates greater torque multiplication, which reduces the 60-foot times of the vehicle, which is where most of the e.t. is made.
For a little converter guidance, we hit up the folks over at TCI. They’ve been building race-proven and affordable converters for a long time and know that choosing the right combination can make or break a drag car. As TCI’s Stanley Poff relayed, “When choosing a torque converter, it’s important to have a complete idea of what you intend to do with the car and all the pertinent information such as engine size, cam specs (lift and duration, lobe separation, etc.), fuel delivery system (carb, EFI, etc.), power-adders (supercharger, turbo, nitrous), rear gear ratio, tire size (height and width), and type of transmission you intend to use and relay that information to the technical person you’re dealing with. Otherwise, you’re taking a shot in the dark at getting the right torque converter for your vehicle.” So, make sure you buy from a company (like TCI) that offers technical assistance and that can tweak an off-the-shelf converter to fit your particular performance envelope.
To test this out we hit up Tim Lee of Don Lee Auto. He had a super-clean, 4L60E-equipped ’98 Z28 just itching to go quicker on the dragstrip. The only mods so far were some 3.73 gears in the stock 10-bolt and a pair of grippy drag radials on a spare set of 16-inch rims.
01 Installing a new converter is as easy as doing a transmission swap. After dropping the starter, Tim Lee pulled the driveshaft, disconnected the fluid lines and wires, then unbolted the 4L60E from the LS1 block. To make life less messy, he dropped the trans pan and serviced the filter prior to dropping the transmission. This way much of the fluid was already out of the trans.
02 The star of our show was this TCI Super StreetFighter torque converter with a billet cover (PN 242937, $893) that we picked up from Summit Racing. It featured furnace-brazed fins, needle bearings, and a hardened hub. The converter came computer-balanced from TCI, so it was ready to rock right out of the box. As you can see, it’s quite a bit smaller compared to the stocker and was several pounds lighter as well. To better match the torque and horsepower of our LS1 engine, TCI custom-modified our converter with a number seven top and 082 stator.
03 Before placing the new TCI converter into the 4L60E trans, we pre-filled it with some fluid. According to TCI, this converter should flash around 3,600 to 3,800 rpm in our test car. Remember, in a street car you need to strike a balance between track performance and driveability. Too low of a stall speed and the car will have idle issues and lower rpm driveability problems. Too high of a stall and you’ll end up with excessive transmission heat and will actually lose e.t. due to the converter stalling too much.
04 Here you get a good view of the billet cover on the TCI converter. Normal covers tend to flex under high torque and stress, causing them to crack, break, or balloon. As Stanley Poff of TCI explained, “Ballooning happens when a converter isn’t built or constructed in a fashion to handle a higher horsepower application and is stressed from the internal pressure coming from the transmission/converter charge that has been increased. It can also happen because of too much internal pressure due to higher rpm and greater pressure created on the inside of the torque converter by opposing forces.
05 With the converter in place, we reinstalled the 4L60E trans and hooked everything back up. One nice aspect of a converter is how stealthy it is.
06 Even a properly sized converter will generate quite a bit of heat. To address this we picked up a TCI Max-Cool transmission cooler (PN 824102, $82). It measured 6x11 inches and had 3⁄8-inch hose barbs. We plumbed it in after the factory trans cooler, which is integrated into the radiator. So, the hot fluid exits the transmission, is cooled by the GM cooler, and is then further cooled by the TCI unit before returning to the transmission. The mounting location, just in front of the radiator, will ensure plenty of cool air. You can also see how we modified the front spoiler so we could pass the hoses through.