many times have you heard, "that guy has a 5000 stall converter or", "that
guy runs a 5500 stall converter". Somewhere along the way in our industry
we mistakenly labeled torque converters by a stall speed figure. At that
time, during the seventies, the industry was trying to emphasize the fact
that the new small type converters, 10", 9" & 8" gave much higher stall
speed than the original equipment converter that came in the car.
This misunderstanding has mushroomed and we now spend much time on the phone trying to explain (to someone with limited knowledge of torque converters) that we cannot sell him a 5000 or 5500 rpm stall converter, because in fact there never was one as they understand it. People who ask for 5000 stall converters expect that when they put it in their car they will be able to put the car in low gear, apply their foot on the brake and bring the engine up to 5000 rpm, and then let it go as the light turns green. This is not how a high stall conventional torque converter works. They actually work on a torque applied basis. Let's set a simplified example by using a Turbo Action #17508M-38 torque converter, which is an 8" Opel type converter made to fit a Chrysler "727' transmission. If we took this converter and bolted it behind a stock 360 cu. in. Dodge engine, it would produce a stall speed in low gear, with a good set of brakes and adequate weight on the rear wheels of approximately 2500 rpm. If you were to nail the throttle to the floor when the light turns green on the Christmas tree, you would get approximately 3700-4500 rpm flash stall speed. These stall figures vary as shown) due to a variation in horsepower levels of various 360 cu. in. engines.
Now lets put a stock 440 cu. in. engine in front of this same converter and with the car in low gear, a good set of brakes and adequate weight on the rear wheels the stall speed would be approximately 3000-3800 rpm. Nailing it from the Christmas tree, approximately 4800-5200 rpm flash stall. Why the difference? Torque! Torque applied from the two engines is much different. A 1974 Dodge 360 cu. in. 4 barrel produces 285 ft. Ibs. @ 2400, a 1974 Dodge low horsepower 440 cu. in. 4 barrel produces 350 ft. Ibs. @ 2400. The torque converter actually sees 65 ft. Ibs. more torque at 2400 rpm from the 440 than the 360. This means that the 440 has more power to cause the torque converter internally to slip. This explains why various engines produce more or less stall speed, but another factor why we cannot hold the brakes and bring up the stall to 5000 rpm is that the first gear in the transmission provides enough mechanical advantage to overcome the brake system and tries to turn the wheels. Contact Turbo Action if you desire to get a fairly accurate stall speed reading.
You say engines determine stall speed, is it true then that you can change the stall speed of a converter? Yes, torque converter manufacturers can change the stall speed but only within the limits of the engine that it is used with. Such as a 360 cu. in. could be varied approximately 1000 rpm with internal changes in our #17508 converter. A 440 could be varied about 1500 rpm with internal changes in our #17508.
A word of caution. The higher the stall, the greater the slippage in high gear. This could mean slower E.T's so when ordering a converter, let the manufacturer try to help you choose the right converter for your application.