Using Dyno graph to figure/adjust shift points
12-17-2010, 02:23 PM
#3
1-2 and 2-3 you shift both at 6800? Is that by the factory tach (is it accurate?) or off another means?
My car last track visit was shifting at 6300 when I watched the shifts. I imagine I am losing a decent bit if it is accurate in MPH/ET that extra 500 RPM.
My car last track visit was shifting at 6300 when I watched the shifts. I imagine I am losing a decent bit if it is accurate in MPH/ET that extra 500 RPM.
12-17-2010, 02:41 PM
#4
No , I have a harland shift light set at 6800. On my Nova i shift out of first around 7000, and out of second around 7200. this is by a real tach, not the factory junk. I am about 2 mph faster in the nova shifting high then if i shift at 6500. Makes a difference on my car but it has more cam then it needs.
the trans am is the same, it dont like being shifted to low.
the trans am is the same, it dont like being shifted to low.
12-18-2010, 10:50 AM
#5
My philosophy is shift for highest average HP.
NA stock cubed manual cars are fairly straight forward. With the wide spacing in of the stock gears, the simple answer is to run most cams as high as your engine is capable of supporting. Dropping below 5000 rpm costs power.
With an auto running an unlocked high stall, the answer is not as simple as the stall does not fall all the way back and some stalls provide extra torque multiplication on the upshift. So you need as a starting point need to know where the rpms drop to when you shift at 300 rpm past peak, 500 rpm past peak and as much as 700 rpm past peak as a starting point. The bigger the stall, typically the less you have to go past peak in order to achieve the highest average power.
NA stock cubed manual cars are fairly straight forward. With the wide spacing in of the stock gears, the simple answer is to run most cams as high as your engine is capable of supporting. Dropping below 5000 rpm costs power.
With an auto running an unlocked high stall, the answer is not as simple as the stall does not fall all the way back and some stalls provide extra torque multiplication on the upshift. So you need as a starting point need to know where the rpms drop to when you shift at 300 rpm past peak, 500 rpm past peak and as much as 700 rpm past peak as a starting point. The bigger the stall, typically the less you have to go past peak in order to achieve the highest average power.
12-20-2010, 11:22 PM
#6
You probably can't rev it high enough to do this, but the proven idea is to shift at whatever rpm will give you the same driveshaft torque after the upshift as you had before the upshift. That results in the best acceleration.
Assuming good lifters, springs, pushrods and rod bolts, you should be holding first to 7200.
Assuming good lifters, springs, pushrods and rod bolts, you should be holding first to 7200.
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12-21-2010, 02:06 PM
#10
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It depends on how well the power carries. Some setups peak and the drop off sharply, others carry the power well for another 5-700 RPM. Could you post the graph up?
12-23-2010, 06:15 PM
#13
That's exactly why you have to look at the curve. The old rule of thumb of using 300 rpm came from the days of racers running tight LSA cams (e.g. 106 - 110) that made great midrange and tend to drop off quickly after peak. Higher LSA cams w/o a lot of advance ground in tend to carry very well.
A stock LS3 peaks about 5800 - 5900 rpm. Shift lower than 6500 rpm and MPH drops. Same thing with the LS7. Stock peaks at no more than 6300 but HP is almost flat to 7000. Best MPH comes from running it to redline.
12-23-2010, 08:33 PM
#14
I think every car and combo is a little different.
I have heard some pick up by short shifting 1-2 300-400 rpm bellow peak to use the verter to multiply TQ and then over rev (past peak) by 300-400rpm on the 2-3 shift.
But some verters that doesn't work with and shifting 300-400 past peak both gears might work better.
Or even 100-200 above peak.
Set your shiftlight at say 6,400 as a starting point. Make 2-3 passes shifting 1-2 and 2-3 there. Then keep the 1-2 shift there but move the 2-3 up a second or so after the light goes off. See if it went faster. If it did, find the sweet spot for the 2-3 keeping the 1-2 at 6,400. Once you found that, Keep the 2-3 at the same rpm but work on the 1-2. Move the light to 6,500 for 2 passes, see what it does. Then 6,600 again for 2 passes. Keep moving it until you find the sweet spot on the 1-2.
I have heard some pick up by short shifting 1-2 300-400 rpm bellow peak to use the verter to multiply TQ and then over rev (past peak) by 300-400rpm on the 2-3 shift.
But some verters that doesn't work with and shifting 300-400 past peak both gears might work better.
Or even 100-200 above peak.
Set your shiftlight at say 6,400 as a starting point. Make 2-3 passes shifting 1-2 and 2-3 there. Then keep the 1-2 shift there but move the 2-3 up a second or so after the light goes off. See if it went faster. If it did, find the sweet spot for the 2-3 keeping the 1-2 at 6,400. Once you found that, Keep the 2-3 at the same rpm but work on the 1-2. Move the light to 6,500 for 2 passes, see what it does. Then 6,600 again for 2 passes. Keep moving it until you find the sweet spot on the 1-2.
12-29-2010, 09:13 PM
#19
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looks like power was dropping. On my dyno sheet it leveled off like that at the end after they let off. Looks like they lifted at 6700rpm. That engine should be spun to 7K though IMO or something close to that.
