Q&A / Tech

Mailbag: Choosing a Transmission and Torque Converter for Racing

Q: I have some questions about a torque converter for my engine combination. The car is a 1981 Malibu that weighs 3,500 pounds. It has a 388-cubic-inch small block with 11:1 forged pistons, Brodix Track One cylinder heads, Crane roller cam (260-degree/270-degree duration at .050-inch lift, .611-inch/.615-inch lift), a Holley 750 carburetor on a Weiand Team G intake, and 1 ¾-inch primary tube headers. I am also running a 250-horsepower nitrous oxide system, 4.88 rear-end gears, and 27-inch tall tires.

I have two transmissions to choose from — a Turbo 350 and a Powerglide with a 1.76-ratio first gear. Since this is a race car, which transmission would be better, and what type of converter should I use?

A: Considering how much the Malibu weighs, we would use the Turbo 350. If your car was 3,000 pounds or lighter, the Powerglide would be the better choice. As for a converter, we’d suggest something that stalls in the 4,400-4,800 rpm range. That stall rating will vary depending on your engine’s horsepower, torque, weight, and rear-end gearing.

On a side note, your engine’s compression ratio caught our eyes. Crane recommends a minimum 12:1 compression with that particular camshaft because of the 106-degree lobe separation, which will bleed off cylinder pressure. Lobe separation is also extremely critical when using a high-horsepower nitrous system.

This is another in a series of weekly Q&A Mailbag sessions with Summit Racing‘s tech department, in which there are hundreds more. Click here to see them all.

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