How do you figure your best shift point?? seat of the pants, dyno, both??

 

You should shift at your engine's peak torque. Since gearing is torque multiplication, going past the peak torque starts to decrease your accelleration. Feet per second speed drops even though you are still accellerating. Grabbing another gear brings the torque curve back down and you start to accellerate faster as the torque starts to build again.

Your shift light should come on at or just before the 1/4 mile mark when in high gear (1:1) if gearing, shift point and tire size are all matched properly. You should be shifting into high gear just before the 1/8 mile mark and the last 1/8 mile is a brute force, high hp pull in high gear to the finish line.

I only shift at 6000 rpm with the powerglide but go through the traps at around 7200-7400. I have my rev limiter set for 7700 since my valves will start to float at 7800.

The engine's red line, not shift point, is usually when the valves start to float. That little red pointer on the cheap tachs is usually used for a shift point but it's supposed to be for a red line of the engine.

 

so if my cars TQ peak is at 4600rpm, i should shift at 4600rpm?? doesnt sound right too me
peak HP is at 6500rpm

 

You know after reading all that I can see the mistake. You "launch" at the peak torque and shift at the peak HP. My bad.

I only have to do one shift. Usually the sooner I'm in high gear, the more consistent the run is.

 

i had a feeling it was a slight mistake, just wanted too make sure because i know you are a racer

 

Everything else about my original response should still be correct in the theory.

When you shift, the amount the rpms drop depends on tranny gear ratios and converter stall speed. That's why the 700R4 is not a good racing tranny. When you do the 1-2 shift, the gear spread is so far apart between those 2 gears that the rpms drop down too far. The engine has to struggle briefly to get back into the best power curve. Theoretically you should stay at the peak hp for as long as possible but since you would need a variable speed transmission to do it, that would be impossible to do.

Top fuel and Funny car have gotten around gear ratio problems by using direct drive. As they launch, the clutch engages progressivly allowing them to get up to speed until it's fully engaged. They never have to shift a gear.