Automatic Transmission Performance - Auto Tech

Stock car racing and automatic transmissions aren't two things that you normally think of going together. But you can find automatic transmissions at racetracks across the country, and they are helping to provide some pretty good competition.

You will mostly find automatics in Street Stock-level racing classes that demand most of the driveline components in the car be stock or stock-replacement. Of course, these are also some of the most popular classes out there because they are aimed at keeping the costs contained and the technology simple so that just about anyone can try their hand at racing. But just because it may be an entry-level class doesn't mean that you can be successful running a bone-stock transmission in a season of racing action. That's a recipe that will likely leave you frustrated with multiple breakdowns or various nagging problems that will have you spending more time with your hands gripping wrenches than a steering wheel.

Instead, we went to Scott Miller of TCI to get some tips from the experts on how to race successfully-and inexpensively-with an automatic transmission. TCI is one of the top builders of performance automatic transmissions and transmission upgrade kits in the country. And while many performance trans builders are still geared solely toward the bracket drag racing market, TCI has noticed the growing trend of automatics in stock car racing and has specific technologies just for the stock car racers.

Try The Turbo
When it comes to stock car racing with an automatic transmission, the Turbo 350, found mostly in Chevrolets, is by far the most popular option. Often, it's also one of the few allowed in the rulebook. Miller says one of the reasons for its popularity is that you can safely run it in Second gear and get the engine into a higher rpm range.

"One thing about running the Turbo 350 is everybody will have an opinion on how to get it to run on the racetrack," Miller adds. "You don't really want to use a stock configuration for shifting the valve body. Some people will tell you not to hook the vacuum to it. Others will tell you not to hook up the kickdown linkage and it will work fine. Well, it will work, but it will also burn up a lot more quickly in racing conditions because that's not the way it was designed to be used. The best answer is to put a full manual valve body on the transmission and then once you are racing, change the fluid and filter about every couple hundred laps. Adding a mechanical valve body isn't hard. You can even do it while the transmission is still in the car. And as long as you have a good transmission when you started out, you should be fine."

Make Your Life A Little Easier
This tip won't exactly make you any faster on the racetrack, but it will definitely make your life a little easier. Most transmissions don't come from the factory with a drain hole in the oil pan. Working on the transmission or completely draining the fluid requires removing the oil pan-and the oil always spills out the sides and gets everywhere, including on you. This isn't as big a deal in a street car because the transmission fluid isn't changed that often. But if you are going to change the trans fluid in your racecar after every 200 laps, this can quickly become a very big hassle. Spend a little money on an aftermarket oil pan for your transmission that includes a drain plug. It will make regular maintenance a lot easier.

Keep It Cool
One of the problems that come with racing an automatic transmission with a working torque converter is that there isn't a direct mechanical linkage between the engine's crankshaft and the driveshaft. The transmission uses a fluid coupling which allows the car to idle with the transmission in gear. Using a performance torque converter instead of an inefficient stock converter will cut down a lot on slippage, but the fluid coupling will still produce heat.

So if you are racing with a working torque converter (instead of a dummy converter that provides a direct mechanical linkage) you should definitely also run a transmission oil cooler. This is because the cooler you keep your transmission fluid, as well as the components in the transmission, the better and longer it is going to work. And racing definitely produces much more heat than the street service the transmission was originally designed for. So if your car isn't already equipped with a cooler, you can actually save money in the long run by investing in one.

Miller recommends buying at least a medium-size cooler. "About a 20,000 to 22,000 gvw-rated cooler is normally fine," he says. "Stay away from the one-way flow coolers because if you somehow mess up and get it hooked up backwards, that can cause problems with the transmission. And those one-way style coolers can plug up. Say you have a transmission that goes out, and it gets a bunch of contaminants in the cooler. The one-way cooler will clog up and the only thing you can do with it then is throw it away."

Avoid Fluid Failures
Speaking of keeping your automatic transmission fluid clean, the fluid you choose can also dramatically affect performance as well as the lifespan of your transmission. "When it comes to fluids, just make sure you run a good quality ATF. It doesn't have to be a pure synthetic, but just make sure it's better than the dollar-a-quart stuff you can buy at the local parts store," Miller says. "You should also plan to change your fluid every 200 to 250 laps.

"And you should also know that not all fluids are the same. I can't speak for other manufacturer's ATF fluids, but I can speak about our two different types as an example. Our Max Shift STF is our top-of-the line synthetic fluid. But then we have Max Shift RTF. That's a Dextron 3/Mercon-based fluid that has a moly additive in it. What that does is the moly actually does bond to the metal parts better. And with heat buildup, it doesn't break down. It stays bonded to the planetary gears and washers and the sealing rings and things like that to cut down on wear. By using a fluid like that it will actually help the transmission run a little cooler."

Miller also recommends making sure you run the correct dipstick for your transmission. Many racers will plug the hole for the dipstick tube and fill the transmission case with fluid. But overfilling the transmission can lead to fluid blowing out the vent or leaks at the seals. And the last thing you want is to get black flagged because you are blowing oil onto the track.

Find The Right Converter
One of the biggest advantages you can find on the racetrack is by using the best torque converter for your needs. You might think a torque converter with a higher stall speed (the rpm level at which the transmission reaches maximum lockup) will give you an advantage because it should allow the engine to get up into a higher rpm range before kicking in, but Miller says that really isn't the case.

"If you are a drag racer, you want a converter with a fairly high stall speed, but in stock car racing, that isn't helpful," he says. "A higher stall in circle track racing means more slippage. And more slippage means less power is getting to the ground. The other issue is a high-stall converter can actually help cause things like wheelspin. Because it doesn't kick in until the engine has reached a high rpm level, and when it does kick in, it kicks in real hard and the driver can have an issue coming out of the turns.

"So you don't want to put a converter for a drag-race car or a street application into your racecar. We've designed converters specifically for circle track racing. They are very low stall and have good torque multiplication, so they lock up quickly and there is very little power wasted. That's the key so when the car comes out of the turns and you get on the throttle, you don't have that slippage in the converter. You are getting the power to the ground.

"As far as TCI, when we build a torque converter for stock car racing, we put in special stator and fin combinations that allow us to give the racer maximum converter lockup. As much lockup as you can get with a fluid coupling mechanism and yet have good torque multiplication. It has come from extensive testing specific to stock car racing-which is certainly different from drag racing-and it makes a difference. The biggest thing is that our converters are more efficient, even at the low stall speeds. For example, if you run a stock torque converter, or a stock replacement converter you can get from your local parts store, slippage can be anywhere from 12 to 15 percent. That's on a perfectly good converter built to stock specs that has no defects in it. Our converters are 98 percent efficient. That means we can cut your slippage from 15 percent down to 2 percent. And you'd better believe that makes a difference on the racetrack."

Ultra-High Performance Options
So far we've only talked about performance options that require only a minimal investment. But there are even better options out there for racers looking for the ultimate in performance from their automatic transmission. For teams racing the Turbo 350, TCI has developed what it calls a Posi-Drive technology that provides 100 percent fluid coupling. It requires a special transmission and converter package from TCI, but the result is no power loss, instant acceleration as soon as you hit the gas pedal and improved engine braking. Efficiency is so good that TCI's engineers say you can expect to see your engine run 200 to 400 rpm less with the Posi-Drive setup.

If your rulebook doesn't limit what transmission you can run, you may want to take a look at a Powerglide setup. Miller says the Powerglide has an advantage over even the Turbo 350 in that it has a lower rotating weight at approximately 20 pounds and pulls less horsepower. That means more of your engine's power is available at the rear wheels. Miller says tests have shown that a well-prepared Powerglide pulls only 18 hp in high gear. Additionally, TCI offers Powerglide transmissions with a complete mechanical lockup, meaning no power losses from a traditional fluid coupling system.

If they aren't disallowed in your rulebook, you may want to think about running a Powerglide automatic. Compared to most other automatic transmissions out there, the Powerglide has less rotating weight and pulls less power from the engine in high gear.