The Stovebolt Site Forums The Shop Area Driveline Torque convertors

I pick my 700r4 up tomorrow and I'm going to be replacing the toque convertor as well. Now comes the questions I was asked. Do you want a 10, 11 or 12 " and what stall? Uh beats me. I have a SB 350 .030 over RV cam headers, 4 bbl may be around 300 HP with a 700r4 and 3.73 rear truck weighs in just under 3200 lbs.. I have been reading all night and it's all so confusing. Stay with the stock convertor thats less efficient or a 2200 - 2800 stall 10 " smaller convertor less heat? I'm getting cross eyed. Any tried and true suggestions? Useage wise cruising around & highway travel maybe a little tire bark now and then. Any advice appreciated.

Don't go too small on the converter diameter. You'll get a "false neutral" until the engine revs up, and then you'll squeal the tires or stall the engine every time you launch. Unles you've got a very radical camshaft that needs to have some RPM built up to get into its torque band, a converter stall speed of 2,000-2,200 RPM should work well. Stock converters usually stall at 1,500 RPM or less which might not let your cam build enough torque for a good hole shot.

"Stall speed" is the point where the engine cannot accelerate any further at full throttle with the brakes locked down due to the converter developing a hydraulic lock. No matter how much torque is applied, the engine simply cannot increase speed. Somedthing will break first. If you pick a converter with too high a stall speed, you've got a race-only setup, unsuitable for street use.
Jerry

Thanks, I was down at Dacco today and their tech guy is trying to get me to buy the 10" 2200-2800 stall. I gave him all the info type of driving, engine, weight, gear ratio and thats what he reccomended. I'm at the age where I probably won't be pulling hole shots. LOL. I was looking for a efficient yet effective application.

I believe I'd go with a little larger-diameter converter, maybe an 11" if it's available. The diameter of the converter directly affects the stall speed, and the centrifugal force on the fluid affects the spin rate from the "pump" section of the converter to the turbine, which is splined to the transmission input shaft. In between the two is the stator, which redirects the direction of flow of the fluid and allows the unit to multiply torque. Once the input shaft starts to move, the torque boost goes away and the converter acts similar to a manual clutch. All torque converters have a 10% RPM slip built in which cannot be engineered out of the design. This is why some converters include a manual clutch that applies at highway cruise speed to make them more efficient. There's nothing new about that idea- - - -the 1949 Studebaker automatic transmission and the 1955 Packard Ultramatic transmission both had a lockup clutch built into their converters. All GM did in the mid-1980's was put a computer in the game.
Jerry

The one that came out was a 12" and probably a stock unit. I wanted to put a new one in since going through the transmission. I know the old one when I put it in gear if I did not hold the brake hard the tire would chirp on the garage floor. There's probably nothing wrong with it. I'm going to take your advice and see if I can get an 11 inch. They will probably have to order it since they did not have any 27 spline units in stock.