Posted in  Drivetrain, Tech Stories

Going Automatic: Getting The Most From Your Automatic Transmission

Circlematic Transmission

In many forms of circle track racing, the ability to “grab a gear and go” is an important element of the setup. However, where track or series rules specify the use of stock or stock-replacement parts, it is often beneficial to use an automatic transmission in dirt cars.

Four-cylinder Mini Stock, eight-cylinder Street Stock and SportMod or similar applications can especially gain an advantage in lap times through the use of an automatic. They are the preferred transmissions for the aforementioned classes running under the IMCA and WISSOTA banners. And believe it or not, automatics are also often available at a lower price point than manuals.

The venerable GM Powerglide is the top choice for most automatic race cars.

“There is less rotating weight when compared to a stock-type manual clutch assembly, so (a Powerglide) is easier to drive deeper in the corners and allows the motor to come up quicker when coming out of the turns,” says TCI’s Scott Miller, whose company’s popular Circlematic package is based on a stock Powerglide that is completely remanufactured and updated in several areas.

“A Powerglide has fewer rotating parts when compared other automatic transmissions and the overall weight is around thirty pounds less.”

There are a few areas to keep in mind that will allow you to get the most out of your automatic transmission package.

The biggest advantage to be found on the racetrack is through the use of a good torque converter. Contrary to popular belief, a high-stall speed is not actually beneficial in circle track racing. A higher stall means more slippage, which results in less power getting to the ground when accelerating.

A high-stall converter can also cause problems like wheelspin because it doesn’t completely engage until the engine has reached a high RPM level. Therefore, you don’t want to put a converter for a drag or a street application into your dirt car.

Circle-track-specific converters, such as those built by TCI, are very low stall so they lock up quickly with very little power wasted. When the car comes out of the turns and the driver gets on the throttle there won’t be any slippage and the power is getting to the ground where it belongs.

Automatic transmissions also use a fluid coupling, which allows the car to idle while the transmission is in gear. The problem here is that this generates heat, which as all racers know is a detriment to performance, or worse, can lead to failure. The easiest solution to a transmission running too hot is to use a cooler.

“We strongly suggest running an external transmission cooler, even if you do not use a working converter,” Miller explains. “The transmission will still build heat without a converter. A cooler will extend the life.”

The cooler you keep your transmission fluid and the components in the transmission, the better and longer it is going to work. However, remember to stay away from one-way coolers that can get plugged up, and mount the cooler where it will receive direct air flow while driving. The optimal operating temperature is about 175 degrees Fahrenheit.

If you run a two-piece coupler, also be sure to keep the coupler and flange lubricated with a high-temperature grease.

TCI’s Miller brings up the need for proper transmission mounting as well.

“Run a rubber rear mount or a “cradle-type” rear mount and make sure that you have plenty of yoke movement by utilizing an extra-long yoke,” he explains.

The urethane transmission mounts that will act as shock absorbers and prevent cracks or breakage as the chassis flexes during hard cornering or when slapping or brushing the wall.

Finally, as in any application, routine maintenance is extremely important in an automatic-equipped race car. Be sure to run a high-quality automatic transmission fluid.

Miller suggests changing the fluid and filter every 175-200 laps, which equates to roughly a month of racing if you count hot laps, heat races and features.

When you change the filter you will also want to check for metal particles. Metal in the transmission filter could mean that the planetary gears are going bad and need to be replaced.

Check the fluid level as well, as loss of fluid can indicate worn or damaged seals. You’ll also want to check the torque on the pan bolts weekly, as rough tracks can literally shake the bolts loose. The transmission should be checked for cracks in the mounts, too.

So there you have it. Gaining an advantage with an automatic transmission is a relatively simple and cheap process.

Essentially it just comes down to using the proper components, mounting them correctly and remembering to perform basic maintenance. All that’s left for you to do is drive into Victory Lane and pose for the cameras.

Source TCI /

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