Tuning/shift points question?
02-08-2009, 10:11 PM
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Tuning/shift points question? I'm not sure if this is the right place to post but here goes! I have an MS3 cam along with heads and full boltons and want to here some advice about where to set the shift points at. Texas Speed says the MS3 cam peak power is at 6400, my rev limiter is set at 6600 at the fuel cutoff, 6200 1-2 gear, 6100 2-3 gear and 6100 3-4 gear. It has been hitting the rev limiter at 1-2 gear only. What should the shift points be at for best performance with this cam? A friend advised me to put the rev limiter at 7100 and the shift points at 6800, all of them, does that sound right? Help me out guys thanks in advance!
02-08-2009, 10:29 PM
#2
Shift points should be at an RPM where more average power is made during each gear. Usually that means shifting past peak power.
The best way is to test different RPMs at the track. You could try finding an online shift calculator that takes gear and tire size into account.
My mild bolt-on car likes the shifts at 6200, so I'm sure your setup would like 6600+.
The best way is to test different RPMs at the track. You could try finding an online shift calculator that takes gear and tire size into account.
My mild bolt-on car likes the shifts at 6200, so I'm sure your setup would like 6600+.
02-09-2009, 10:54 AM
#5
Jon is close, but he's missing a step... you dont want to go by just power at the given RPM point, but you want to go by acceleration at that point. Most cars will accelerate faster in lower gear even if the power made at the crank is higher than the power made at the other RPM point after the shift.
You want to graph out power in every gear, then convert it to acceleration curves per gear, and the spot where the two curves from acceleration in two gears cross, that's your optimal shift point.
You want to graph out power in every gear, then convert it to acceleration curves per gear, and the spot where the two curves from acceleration in two gears cross, that's your optimal shift point.
02-09-2009, 01:27 PM
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Jon is close, but he's missing a step... you dont want to go by just power at the given RPM point, but you want to go by acceleration at that point. Most cars will accelerate faster in lower gear even if the power made at the crank is higher than the power made at the other RPM point after the shift.
You want to graph out power in every gear, then convert it to acceleration curves per gear, and the spot where the two curves from acceleration in two gears cross, that's your optimal shift point.
You want to graph out power in every gear, then convert it to acceleration curves per gear, and the spot where the two curves from acceleration in two gears cross, that's your optimal shift point.
And - just because you set the upshift for a certain RPM doesn't mean that's when the shift will happen. You'll have to apply a bit of a fudge factor since it takes time for an upshift to occur. If you're hitting the rev limiter on the 1-2 upshit, you need to make sure your MPH trigger is low enough first. Then, drop the RPMs down a little at a time so it doesn't do it. Usually, the computer will be thrown off more if there's wheel spin. With traction, you shouldn't need as much of a fudge factor. At least, that's been my experience.
02-09-2009, 02:24 PM
#7
Correct....
And - just because you set the upshift for a certain RPM doesn't mean that's when the shift will happen. You'll have to apply a bit of a fudge factor since it takes time for an upshift to occur. If you're hitting the rev limiter on the 1-2 upshit, you need to make sure your MPH trigger is low enough first. Then, drop the RPMs down a little at a time so it doesn't do it. Usually, the computer will be thrown off more if there's wheel spin. With traction, you shouldn't need as much of a fudge factor. At least, that's been my experience.
And - just because you set the upshift for a certain RPM doesn't mean that's when the shift will happen. You'll have to apply a bit of a fudge factor since it takes time for an upshift to occur. If you're hitting the rev limiter on the 1-2 upshit, you need to make sure your MPH trigger is low enough first. Then, drop the RPMs down a little at a time so it doesn't do it. Usually, the computer will be thrown off more if there's wheel spin. With traction, you shouldn't need as much of a fudge factor. At least, that's been my experience.
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02-20-2009, 12:40 PM
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The rev limiter was set to 6700 and shift points to 6100 all of them. It no longer hit the rev limiter and ran a 12.2 at 112.45 mph with a 1.85/60 ft. I'm not sure if these shift points are exactly squeezing out the motor's full potential. Anyone?
