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Shift Point
Just received my dyno results on my Keith Craft engine. 622HP and 630 TQ.
My question is, what should the shift point RPMs be to maximize acceleration? The TQ peaks at 4700 and the HP at 5800. RPM HP TQ 4700 564 630 4900 577 618 5100 591 608 5300 605 600 5500 615 587 5700 621 572 5900 622 553 6000 619 541 |
I would put a shift light in with a 5700 RPM pill and a rev limiter pill set at 6000 rpms. You are putting down some great torque numbers.
Clois |
I think I would shift a couple of hundred rpm higher than peak hp to stay in the power band after the shift is made.
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I've got that same motor, with a tko600, and a 3.50 9" rear gear, and I've got a few suggestions for you.
First, put the shift-light right in the middle of your line of site somehow. You will NOT want to take your eyes off of what's in front of you if your stomping on the go-fast pedal. Second, the first gear shift light will come real quick, so wherever you set the rev limit, start with a shift point well south of that to start with, and move it up from there. Third, good luck getting thru second gear without lifting! :eek: |
I am conservative
I don't see the need to run up to 6 grand, you are just looking for trouble. I wouldn't worry about shift points. Your numbers and the weight of our cars make traction your problem. I have an orginal 427 with only one more refresh in her. It makes all the power I need before 5000 and never breaks a thing.
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The following is an academic answer that may not hold up to scrutiny from real drag racers, but here goes. Assuming traction is not an issue, acceleration is primarily a function of engine torque. Your shift point should be such that your RPM at the shift is just as far above your peak torque RPM as your new RPM is below after the gear change. For example, if your engine drops from about 5400 RPM in 3rd to 4000 RPM in 4th, you'll stay within 700 RPM of your peak torque in both gears. As you get to higher speeds, wind resistance and horsepower become more important, so higher RPM help.
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Ive heard various discussions over the years for shift point at max torque vs max hp. In this case shift point would be 4700. Consistently I've found the peak torque numbers to be to low in 'real life', all though mathmatically you could make a case for a torque shift point.
4700? Just to low in my opinion, peak hp gets my vote. |
Thanks to all for your responses. It probably doesn't matter when I shift due to the HP and TQ.
That's some good advice Brad. I'll let you know if I can stay in the loud pedal through 2nd.:eek: |
Shift points for max accell
danc30 The magic number is 3-500 rpm past max HP. Any thing past this is just wasting motor. Try to stay within your power band from max torque to max HP numbers. This will help the motor last the longest. Rick L.
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