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Sorting out Torque Converter Confusion Part Three
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Picking the Right Converter
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By Wayne Scraba Photos courtesy of J.W. Performance Transmissions |
Over the past couple of issues, we've taken a detailed look at the reasons why a specialized torque converter is required for your race car, and how specific variables affect the torque converter. That's great, but 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 a racecar combination. The only way to tailor the converter to your combination is to check with the experts (the converter manufacturers). The criterion for selecting the right converter for your combination is extensive and extremely important. Before picking up the phone to order a converter, have the following information ready: RACE CAR CHASSIS
Actual 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 and still remain effective. Body Configuration: 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 the speed traps. For example, an open-top Corvette roadster will push far less air than a '55 Chevy.
PERFORMANCE Class of Competition: The manufacturer needs to qualify your needs as accurately as possible. Because of this question, the manufacturer might find that it already has significant information about your type of combination on file. Further to this, there are major differences between converters for class racing or foot-brake bracket racing or Super classes and so on.
Average ET, MPH, 60-foot times, & RPM at the ET 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 building a new car, the builder can estimate how fast the car will run and help to choose the right combination of components before mistakes (often expensive) in the combination are made.
POWERPLANT When it comes to the powerplant, the following information is required so that the overall combination can be evaluated: Bore and Stroke Type of Cylinder Heads (modifications) Cam Lift, Lobe Centerline and Duration @ .050" Carburetor & Manifold Compression Ratio Primary Header Tube Diameter
TRANS & REAR-AXLE GEAR RATIOS Type of Transmission: Once the manufacturer knows which transmission is in your car, the company knows what low-gear sets are available for your combination. Tail-housing length can help identify the transmission. Rear-Axle Ratios & 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 & 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. Slick Dimensions & Compound: Through extensive testing and customer feedback, racing converter manufacturers such as J.W. Performance Transmissions have identified the characteristics of many drag 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 to the above, the manufacturer will require information on your fuel type and whether you use nitrous oxide or if the engine is supercharged or turbocharged. The tach type is considered and the builder will ask for information 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. Special thanks to J.W. Performance Transmissions for supplying critical information provided in this article:
J.W. Performance Transmissions 1826 Baldwin Street Rockledge , FL 32955 PH: 321-632-6205 |
