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Torque Converter Selection - Transparent Performance

Picking The Right Converter Is The Key To Performance

By Wayne Scraba

Picking The Right Converter
How do you know which converter is right for your application? It's almost impossible to buy a converter "off-the-shelf" and expect it to be right for your car. The only way to tailor the converter to your combination is to check with the experts (the converter manufacturers). ATI builds hundreds of different 8-inch converter combinations and has computerized over 7,000 different vehicle combinations.

With the criteria so variable, most aftermarket manufacturers require the following information:

Chassis
Vehicle weight: This 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 and still remain effective.

Body style: An initial calculation of the horsepower/gear ratio will be done. Then it might have to be adjusted if the car in question 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
Street car, street/strip car, or bracket racer? The manufacturer needs to qualify your needs as accurately as possible, because they might already have significant information about your type of combination on file. Further to this, there are major differences between converters for class racing or bracket racing or street/strip duty.

Average e.t., mph, 60-foot times, and rpm at the e.t. light: The manufacturer wants to see what the present performance capability is with your combination. How efficient is your converter? How efficient is your entire combination? If you're building a new car, they can estimate how fast the car will run and help to choose the right combination of components before mistakes are made.

Engine
When it comes to the engine, the following information is required:
*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
What type of tranny (and its gear ratios), rear gear ratio, and tire size: This 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.

Suspension & Tires
Type of rear suspension: This is 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.

By Wayne Scraba
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