TCI’s Circlematic: Top Powerglide Secrets Revealed

Once considered too weak to be a real racing transmission, the reliable Powerglide began to find a second life with circle track race teams in the early ’80s. Slowly gaining respectability, the workhorse transmission had become popular and desirable by the ’90s. By that time, the Powerglide had been discontinued for twenty years, having last seen service as a low cost option for the six-cylinder Novas and four-cylinder Vegas before being completely phased out in 1973. However, its simple design, reliability, and strength have put the Powerglide at the top of the “must have” list for many circle track racers. 

Before the Powerglide transmission, circle track racing and automatic transmissions didn’t go together. Now it would be tough to find a grass roots Street Stock level racing class that didn’t use an automatic as the staple transmission. For these classes where stock or stock replacement parts are mandated, the Powerglide transmission really shines.

Just having a bone stock Powerglide in an entry level class doesn’t guarantee that you will have success on the track. Finding out how to take advantage of the Powerglide’s strengths and minimize its weaknesses will take a racer to the next level. For the inside scoop on upgrading a stock economy transmission that was once thought of as “weak-kneed,” we went to our guys at TCI Transmissions. Scott Miller of TCI gave us the lowdown on how to make your automatic transmission race successfully while running on a budget with the venerable Powerglide Transmission.

TCI's circle track version of the reliable Powerglide Transmission. The "Circlematic" is available in several different configurations.


Why Use An Automatic Transmission?
Why should you use a TCI Automatic transmission? Cost and weight. “Compared to a good four-speed transmission, the TCI Powerglide in basic setup will cost $300 to $500 less and is 50 to 60 pounds lighter,” explained Miller. “The weight alone saves wear and tear on the valve train and drive train.” He also pointed out the fact that TCI’s Powerglide has an outstanding performance record.

Working with several racers over the past few years, Miller claims that TCI’s Powerglide is more responsive off turns than standard shift transmissions and the engine picks up much more quickly. Additionally, he tells us that the Powerglide even has an advantage over the Turbo 350, in that it has a lower rotating weight at approximately twenty pounds and pulls less horsepower. This means that 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. TCI also offers Powerglide transmissions with a complete mechanical lockup, meaning there are no power losses from a traditional fluid coupling system.

The latest and greatest in TCI’s Powerglide line is the Circlematic transmission. Scott explained the research that went into developing the valving for the Circlematic transmission. They spent “many days out on the dirt tracks getting the jetting set for the reverse and low” passages in the valve body, and according to Miller, the newest internal control powerglide valve body is the next generation in circle track valve bodies. 

The direct drive Powerglides started out with a ball valve that operated the valve pressure control from the cockpit. This system was eventually replaced with a clutch pedal control, which is still common in many of the modified and late model series. TCI’s latest valve body is controlled internally, freeing the racer of all external controls and enabling them to concentrate on the competition. The fully manual shift valve body controls line pressure internally and automatically. Miller states: “All you have to do is put it in gear and mash the accelerator.” As an additional bonus, the new valve bodies can be ordered in either the standard shift pattern, or a reverse shift pattern that allows for upshifts without worrying about hitting neutral or reverse.

The TCI Circlematic valvebody, available in standard or reverse shift pattern.


Top Ten Secrets of TCI Circlematic Powerglides and Converters
TCI’s Circlematic Powerglide is basically a stock Powerglide transmission that is completely remanufactured and upgraded in several key areas. With a significant amount of coaxing, we got Scott to give us the breakdown on the upgrades that are made to the Powerglide transmission before it can earn the title of “Circlematic.”

TCI's Circlematic upgrades for Powerglide transmissions.


1) High Performance Clutch and Steel Plates — Scott points out that “factory clutches were designed for factory cars operating in street conditions.” TCI upgrades the Circlematic transmissions with Alto clutch and steel plates, which are designed for higher performance applications. Material composition has come a long way since the Powerglides were initially manufactured at the factory, and TCI has taken advantage of this by using a Kevlar band in the transmission. Whereas the original clutch assemblies were capable of 350 horsepower, these components are rated between 550 to 600 horsepower.

2) Five Clutch Plates — The stock Powerglides were produced with four clutch plates for V8 applications and three clutch plates for 4 and 6-cylinder applications. Every TCI Circlematic transmission is configured with five clutch and five steel plates. The additional plates ensure that the transmission will not experience slippage on the track.

The Circlematic's modified planetary gear set.


3) Modified Planetary Gear Sets — The standard configuration of the Circlematic Transmission includes a remanufactured factory gear set. Where this unit differs from the original is in the details. The TCI version incorporates welded pins and a modified output spline shaft to allow for an extended yoke. Dirt track cars experience a lot of rear end and driveshaft movement, more than a stock designed transmission can handle sometimes. This can result in cracks in the extension housing or bell housing of the transmission, not to mention seal damage in the front or rear transmission seals. 

The gear set also features a standard 1.82:1 low gear with a 1.00:1 ratio high gear. As an option, TCI offers a variety of low gear ratios as well. Everything from a stout 1.65:1 to a “granny” 1.98:1 can be installed at TCI.

The Circlematic features a specially designed oil pan with stock depth and a stronger material that dissipates heat better.


4) TCI Designed Oil Pan — The oil pan on TCI’s Circlematic transmissions is an in-house designed aluminum case that is normal stock depth but stronger. Scott told us that he has seen “some of the stamped thin steel pans actually rip off of the transmission under severe racing conditions on rough tracks.” In addition to being a stronger component, it provides extra strength to the mounting area of the transmission. The aluminum properties of the pan help to dissipate heat, and a cooler transmission is a happy transmission.

The Circlematic valve body features internal bleed passages that are adjustable by changing the jets.


5) Valve Body — TCI’s Circlematic valve body is the crown jewel in the Circlematic line of transmissions. Due to the design and engineering work done by TCI’s engineers, circle track drivers can use an automatic transmission in direct drive without external valves or clutch pedals. The TCI Circlematic valve body is designed with an internal bleed off in the forward chamber and one in the reverse chamber, all activated by the driver’s manual shift of the transmission. The mainline pressure is preset to ideal working parameters at the factory and the pressure settings require no adjustments. The bleed off engineering in the valve body has a distinct advantage of reducing drag on the front pump due to excessive pressure buildup. Finally, and this is where most dirt track racers feel it the most, this valve body costs less to operate. Because it is used in a direct drive setup, there is no need to purchase a torque converter. It saves dollars while reducing drag, heat, and slippage. TCI’s Circlematic valve body is an all-star on this team.

6) Front Pump — Another key design upgrade in the Circlematic transmission is the pump system. The front pump is a remanufactured stock pump with oversized gears installed for higher volume, resulting in increased lubricating properties. The trick here is increasing oil volume and velocity without increasing pressure exponentially, and TCI has done it correctly with this lubrication system.

7) Removed Rear Pump — Removing the rear pump and installing a plate with routing passages significantly reduces rotating mass and drag inside the transmission. 

8) HDT coating — TCI worked with a major paint supplier for several months testing a coating that not only looks good, but has a measurable effect on cooling. A functional Heat Dissipating Technology (HDT) coating was developed through the process of trying different coatings and running the transmissions on a dyno. The HDT coating is used not only on the transmission case, but also on TCI’s torque converters, front pumps, and various other components. A cooler transmission and components will last longer and perform better.

TCI's Steel Clutch Hubs resist spline failure and wear.


9) Steel Clutch Hubs — The stock Powerglide clutch hubs were a cast unit prone to fractures, spline failure, and spline wear. TCI upgraded the clutch hub to a steel unit that has less rotating mass in a stronger component and resists the initial shock under power when using a direct drive setup. The Steel Clutch Hub makes the Circlematic a dependable transmission when you’re getting on and off the throttle as hard as dirt track racers do.

10) Triple Tested — “We take the transmission assembly, minus the valve body, and place it on a hydraulic dyno to measure the performance of the transmission’s internal assemblies,” Miller said while explaining the Quality Assurance/Quality Control procedures for the Circlematic Transmission to us. “Simultaneously, we test the valve body on another dyno to ensure that the valve body meets our specifications. Finally, we assemble the entire transmission and run the completed unit on a transmission dyno to verify that the components are working together as a performance racing transmission.” The run information from the final dyno is included in the shipping documents that come with the transmission. There is little doubt that TCI’s Circlematic transmission will run perfectly in your race car as soon as it arrives at your door.

Additional Tips for Powerglide Transmissions
The folks at TCI wanted to share some additional tips for operating a Powerglide transmission on the dirt tracks. Whether you are running a Circlematic Powerglide or an OEM Powerglide, these tips will help you get the most out of your transmission and make it last longer. 

1) Keep it Cool — One of the inherent problems that comes with racing an automatic transmission with a working torque converter is heat. Automatic transmissions use a fluid coupling, allowing the car to idle with the transmission in gear. One solution is to use a performance torque converter that will cut down a lot on slippage. However, the fluid coupling will still produce heat. All automatic transmissions will benefit from a cooler. The cooler you keep your transmission fluid and the components in the transmission, the better and longer it is going to work. 

Racing definitely produces much more heat than the originally intended street use. “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,” Miller advised. “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.” 

Mounting the cooler where it will receive direct air flow while driving will help keep the transmission cool. The optimal operating temperature for automatic transmissions is about 175 degrees Fahrenheit.

TCI's louvered transmission cooler kits.


2. Keep it Fresh — Transmission fluid will affect the performance and lifespan of your transmission. “When it comes to fluids, just make sure you run a good quality ATF,” Miller says. “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.” 

Here is what Miller explained as a good fluid policy:
“You should plan to change your fluid every 200 to 250 laps. 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 Synthetic Transmission Fluid is our top-of-the-line synthetic fluid. The benefits of the Max Shift STF for circle track racers are reduced pump cavitation and more consistent line pressures, because of the anti-foaming agents in the the fluid. At high temperatures, the Max Shift STF is more resistant to high temperature drivetrain wear and fluid breakdown that is common in high performance circle track racing. Then we have Max Shift RTF. That’s a Dextron 3/Mercon-based fluid that has a moly additive in it. The moly actually bonds to the metal parts better, and it doesn’t break down with heat buildup. 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.”

No need to get nervous about using a synthetic transmission fluid in an older style transmission. The only reason to ever be concerned and avoid using synthetics is in transmissions that haven’t been freshened. TCI transmissions all have new seals, gaskets, bushings, and clutch and steel plates. A 27 to 38-year-old transmission needs to be freshened anyway before it’s used in a race car.

TCI Recommends using a racing type transmission fluid for racing applications.


3. Get The Right Converter — According to Scott, the biggest advantage you can find on the racetrack is by using the best torque converter for your needs. Many racers think that a torque converter with a higher stall speed will give you an advantage because it will allow the engine to get up to a higher RPM range before kicking in, but Miller says that actually 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. 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 race car. 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 that you can get from your local parts store, slippage can be anywhere from twelve to fifteen 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 fifteen percent down to two percent. And you’d better believe that makes a difference on the racetrack.”

The Circlematic is tailor-made for the direct drive coupler.


4. Mount it right — Powerglide transmissions have gotten a bad rap when it comes to cracked bell housings and cases. The majority of case cracks are experienced at the rear of the case near the mounting bosses. These problems can be stopped before they even start by making sure that the driveshaft length is correct. Driveshafts that are too short will be prone to excessive cracking and cause vibrations. Urethane transmission mounts are the only means of mounting the transmission. These act as shock absorbers and prevent cracks or breakage as the chassis flexes during hard cornering or kissing the wall. Dirt track car builders should never consider using solid mounts on their transmissions.

5. Routine Maintenance — Getting any transmission to give good dependable service in extreme applications like racing on dirt requires a healthy preventative maintenance approach. Start by making sure that your fluid is changed approximately every 200-250 laps. Change the filter and check for metal particles. Metal in the transmission filter indicates that the planetary gears are going bad and need to be replaced. The transmission should be checked for cracks in the mounts and tight mounting bolts before every race. Check the fluid level. Loss of fluid can indicate worn or damaged seals. Finally, lubricate the spline on the front pump drive with hi-temp grease.

Article Sources

About the author

Bobby Kimbrough

Bobby grew up in the heart of Illinois, becoming an avid dirt track race fan which has developed into a life long passion. Taking a break from the Midwest dirt tracks to fight evil doers in the world, he completed a full 21 year career in the Marine Corps.
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