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So how do you know which converter is right for your application? Frankly, it's impossible to buy a converter off the shelf and expect it to be right for your modified car. The only way to tailor the converter to your combination is to check with the experts: the converter manufacturers. ATI, for example, builds hundreds of different eight-inch race-converter combinations and has taken the time to computerize more than 7,000 vehicle combinations so that the right converter is manufactured for your car.

Hughes makes a valid point about the converter-selection process: "Be sure to spell out and understand the real application for the converter. A Super Gas or Super Comp car doesn't need a converter designed to squeeze the last tenth or mile-per-hour out of the combination. Instead, the combination needs a converter that's engineered for consistency."

The criteria for selecting the right converter are many and extremely important. Before selling a converter, ATI requires the following information; all serious aftermarket transmission and converter manufacturers will require similar information.

Chassis
Vehicle weight: The weight tells the converter manufacturer how much work is needed to reach a certain elapsed time. It affects gear ratio and helps indicate what converter flash rpm can be used in your combination.

Body style: An initial calculation of the horsepower/gear ratio will be made and may be adjusted if the car has a large frontal area. This gives the manufacturer an idea of how much air the car is pushing as it enters speed traps.

Performance
Class or bracket: The manufacturer needs to qualify your needs as accurately as possible; it might already have significant information about your type of combination on file. Additionally, converters for class or bracket racing or street-strip duty have major differences.

Average e.t., speed, 60-foot times, and rpm at the e.t. light: The manufacturer wants to know the present performance rating on your car. How efficient is your converter? How efficient is your entire combination? If you're building a new car, the manufacturer can estimate how fast the car will run and help to choose the right combination of components before mistakes (often expensive) are made.

Engine
The following information is required to evaluate the combination:


Bore and stroke
Type of cylinder heads
Cam lift, lobe centerline, and duration at .050-inch
Carburetor and manifold
Compression ratio
Primary header-tube diameter
Gear ratio
Type of transmission: Once the manufacturer knows which transmission is in your car, it knows what low-gear sets are available for your combination. Tail-housing length can help identify the transmission.

Rear-axle ratios and tire size: This information is required to calculate the actual output gear ratios (overall ratios in the respective gears), engine rpm, and vehicle mph. It is possible to have a good elapsed time and high trap speed but still have a torque converter that is all wrong for your car. Trap-speed rpm will tell you if the converter is operating efficiently when going through the traps. Typically, 100 rpm of torque-converter slippage equates to a loss of 1 1/2 mph through the traps. In essence, too much slippage means that you're throwing away usable horsepower and elapsed time.

Suspension and tires
Type of rear suspension: This information is especially helpful in diagnosing problems with your car or combination. In some cases, a loss of performance has nothing to do with the transmission or torque converter — it's in the chassis.

Tire size and code: Through extensive testing and racer feedback, racing-converter manufacturers have identified the characteristics of many tires. Tire growth, sidewall characteristics, and compounds are taken into account when selecting a torque converter. This testing has also determined which tires work and which don't with automatic-transmission combinations.

Miscellaneous
In addition, the manufacturer will request information on fuel type and ask if nitrous oxide is used. The tach type is considered, and information will be requested on motor-mount midplates, flexplate bolt circle, past performance, past equipment tested, and so on. Expect a barrage of questions before the right converter is selected.

One size doesn't fit all when it comes to torque converters. What's the bottom line? Contact manufacturers directly for an exact recommendation based on your combination. Remember to provide accurate information about your own combination. If you fudge the numbers, you'll end up with the wrong converter, and you won't be happy. That's one thing that can be guaranteed.
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