TCI® Top 10 FAQ

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This FAQ contains the most frequently asked questions about TCI® products. If don't see your question here, please call TCI® directly at 877-776-9824, or visit the TCI® Tech Help.


1. Can you explain incorrect torque converter selection problems?

As owners add engine power, they often install a looser torque converter (higher stall speed), overshooting the power range. A tighter converter will provide more bottom end power. As a guideline, once you crest the 600 lb-ft range, you need to install a torque converter with a billet front cover. Over 800 lb-ft, you need to have not only the billet front cover, but also add in a multi-disc clutch system and steel stator. Over 1400 lb-ft, a custom converter is in order.


2. What is the most common installation error?

Torque converter not engaged in pump drive.

Despite how it may be called out in the instruction sheet, the most common problem causing transmission failure is not engaging the torque converter on the input shaft. If the torque converter is not fully engaged, the pump will burn out, causing transmission destruction. More often than not, the converter appears to be in place, but the final press to full contact is not made. The converter needs to be spun on the shaft and turned until it reaches correct placement. How will you know? The transmission housing will bolt up easily to the back of the engine. If the transmission requires “pulling into place” by drawing on bolts placed in the bell housing to make it fit, the converter is probably not in the right place. Keep turning the converter and pressing it on the shaft. When it finally hits home you’ll hear that pleasing click of completion.


3. What do I need to know when calling the tech line for assistance?

There are a number of important specs that are required to ensure the tech line folks can help you select the right parts for your application. It’s a short list but an important one:

• Engine cubic inch
• Weight of vehicle
• Rear end gearing
• Tire height of drive wheels
• Cam specs (critical for torque converter selection)
• Induction system type (carburetor or fuel injection)
• Any power adders and estimated power increase
• Ultimate usage of vehicle (race, street, towing, etc.)

4. Explain lock up vs. non-lock up transmission – which is right for my street driven car?

A non-lock up converter always has some slippage in the system. This is a common condition in racecars with high stall speed converters, as it allows the power to be delivered to the racetrack in a usable traction-control mode style. Lock up transmissions electronically lock the turbine to the inside cover, giving a solid connection – no slippage. In this case, the turbine is turning at the same rate as the impeller.

As a rule, the tech line folks never recommend non-lock transmissions up for street applications, as non-lock up converters are inefficient for fuel mileage and street performance. Full lock up converters also create less heat and are better for cruising around town.


5. Electronic vs. non-electronic transmissions – which are better for me?

It’s a matter of whether you like to be in control of your transmission’s every feature, or not. Simply stated, a traditional non-electronic transmission, such as the GM Turbo 400, will certainly do the job. These transmissions operated through a combination of mechanical parts that would, more often than not, get you close to what you wanted in terms of performance and shifting.

Today’s electronic transmissions such as the 4L80E are plenty strong and will handle most anything you can dish out – plus offer an overdrive gear set for increased fuel mileage. Further more, they also offer total control of every feature, including both wide-open throttle and part-throttle shifting points. Those are features you won’t be able to dial in with old school transmissions. They take more time and energy to set up and require the use of some computer system. But if you have the ability to surf the internet with your computer, you have the ability to program one of today’s new electronic transmissions. When combined with our TCI® TCU™ (Transmission Control Unit), it is easy to not only program the transmission, but make further alterations later.


6. Do I need a cooler for my transmission?

In a word, yes. And, make it the biggest transmission oil cooler you can properly install on your vehicle. It should be mounted out of harm’s way, and in an area that has free flowing cool air. Being close to radiator hoses and headers is a big “no no.” This can be especially tough with street rods, but should be considered when designing and building these vehicles.


7. The Big Stall – how do I find my torque converter stall speed?

This is easy, but often confused. “Foot Stall Speed” is generally an incorrect figure. Placing the transmission in drive while holding the brakes on and noting the engine rpm before the vehicle begins to move is often a better test of brake condition than stall speed. The real number you need is “flash stall” and here is how to get it.

While driving in high gear (with the overdrive switched off if you have one), in a safe area free of traffic and obstructions, quickly depress the throttle. Note the highest rpm shown by the tachometer before the vehicle begins to accelerate. This is your flash stall speed and the number you need when talking to your tech line rep. It’s that simple.


8. Why can’t I run an 8-inch torque converter in my street car?

Street is not race. There is a difference. The 8-inch racing converters may generate great performance, but they also have high stall speeds, which equate to greater slippage and heat build up. Generally speaking, the higher the performance of your engine and the hotter the camshaft, the looser the converter (meaning higher stall speed). However, there is a limit, and racing converters in street applications is something to avoid.


9. My transmission comes with an assortment of rings that allow me to adjust by speedometer – which one is right for me?

Start by counting the number of drive teeth on the transmission gear you are currently using. If you have your rear end gearing ratio and the height of the driving tires in inches, contact the TCI® Help Line (888-776-9824) and we can help you select the right ring for your application. Or, you can use our online calculator.


10. When should I use a clutchless automatic transmission?

First off, it is not a matter of cost, as the two transmissions have virtually the same cost. Clutchless transmissions are great for circle track competition. They are simpler than transmissions with clutches, requiring fewer lines running through the cockpit and easier installation. Clutchless transmissions use bleed offs to get you going and are a direct lock up system, which does not allow for clutch slippage – and the benefits to efficiency therein. Clutchless transmissions deliver quicker throttle response and immediate application of power making them a good choice if your class of racing allows for this option.