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In the automatic transmission world about how much power does it take to turn each one? I constantly hear that a T-400 uses much more power to operate and uses over 125 horsepower more than a T-350. Is one that much more efficient than another? How much power does each common transmission use?
James Baker, Swansea, IL
This is a good question. I have heard many years ago that in some hot rod magazine, there was a set of numbers put out about all the popular automatics at that time. I had heard of 10 – 20 hp, but if we could find someone to set up and sponsor such a study, we would all be interested in the outcome. 125 hp sounds like more then I would believe. The 350 would surely take less hp to spin because it is smaller and lighter, but it is not as strong as the 400, so each unit has its place.
I have a 350 trans with a 2800 stall converter in front of 411 gears. I just purchased my racecar a month ago from a guy who tuned it down to drive it on the road, where as I would mainly like to drag race it. It has a bone stock 427 that right now shifting at 5500 I'm going 12.80s. What's the best way to tell if I'm short shifting it, or possibly shifting late?
JJ, Madison, WI
The rule of thumb is that we want to run the engine between peak torque and peak hp. So we set up the transmission gears and rear end gears and converter stall to match this band. You really just have to experiment with shift points and launch RPM comparing ET slips. But I think you’re right, maybe 6000 – 6500 is where the power starts to fall off. A little trial and error is your best course.