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Torque converters.

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Cool53:
When you chose a converter keep in mind all the important items, but one of the most important is gear ratio at the rear, and first gear ratio in the transmission. But if you want it all, a big engine with a 2.73 rear axle then you can't have a high stall converter even if it is a lockup. Figure your engine rpm at cruise speed. This rpm should be in the power curve of your cam or you will never get any efficiency, even if the engine is turning slowly, because it is running at an inefficient level. The next thing is that the stall speed has got to be less than or equal to the cruise rpm. If the stall speed is higher then the converter won't be a good fluid coupling and will make heat like a furnace and cause trans overheating.
If you have a street converter it is most likely a flash converter. These only attain their listed stall speed when launched from a low engine rpm. But power braking for stall is much lower than flash stall. An example is in my truck I run a 3500 flash stall street/strip converter, which stalls at 3500 when I stab it. But when I power brake it the stall is about 2600. With 4.10's, a 25" tall tire, the engine runs just a little over 2800@70mph. That works. But I also have lockup, which brings it down to 2600, which gets me just at the bottom end of where the cam starts to work. So I get pretty good mileage and the trans runs cool. Don't give up gear for mileage until you crunch the numbers. You might be going backwards, especially in the power to the wheel department. Run as much as you can stand to guarantee the fun meter goes high.

themoose:
Jef

What ever happened to the concept of a variable pitch converter. Didn't GM offer them at one time? That would seem be ideal setup if it could be engineered to take the abuse.

Moose

Cool53:
Hey Moose,
I just got a 400 in that was a switch pitch. Haven't seen one in years. I think it is a great idea. They were originally used to get the old land yachts like the big Caddies to leave from a set of lights. A fellow emailed me, asking me if I could build him one. I can come up with enough parts for the trans but I haven't found a converter builder that has the parts. And I don't think the moving parts would take the repeated punishment of big torque.
I guess the TCC was the answer, although the switch pitch would be nice. If you find an old GM barge with a switch pitch setup (it will be a THM400) make sure to be careful with the torque converter, keep it clean. If you are lucky enough to find a good one give it a try, you'll love it. Peter Lebonte (sp?) from the Chevrolet dealer in Brunswick, ME used them in all his hotrods. He loved them. Unfortunately Pete passed before his time but left us with some good tips. He was like you,ma great source of information in classes at the GM Traing Center.
If you are looking at parts for a 400 and see a solenoid, the same type as try kick down solenoid, mounted on the back of the pump then you have just found a switch pitch pump. Hang onto it!

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