Hiccup when power shifting....

[Motorboy8769]

https://youtu.be/AHKDX6u1PbI

It shakes the tires in high and brake lights come on almost every time does it when I leave too

[acammer]

Originally Posted by Motorboy8769

It’s a btr blower cam it makes power to 6400 then starts falling off.

If it Peaks at 6400 I would think you would want to shift somewhere north of 6800, the goal being highest average horsepower throughout the gear. What's the Trap speed like?

[Motorboy8769]

1/4 trap speed is 122-123

4 speed with 4.57 gears

[Motorboy8769]

[acammer]

I think you're leaving a some on the table there - and I'll show you why I think that. I took your dyno graph and plotted out a range from shift recovery rpm to redline. It's not exact science because I don't know the exact ratios in your 4spd, but it's based on a third gear pull, coming from a 1.933 second gear to a 1.392 third gear. I also took a pretty wild guess at the curve past peak, but I think that's what you typically see with a setup like you have.

Basically, if you shift at 6400rpm at the top of second the recovery rpm in third is 4600rpm. If you shift at 7000rpm the recovery rpm is 5000rpm. Although the power does roll over past 6400, it doesn't drop off a cliff. If you averaged the power from 4600 to 6400 (blue area) vs. the power from 5000 to 7000 (yellow area) you would find that the higher shift point would yield a significantly higher average hp.

Typically the highest average power is usually achieved with shifts at the maximum rpm the engine will tolerate. Certainly there are exceptions to that in applications where the engine really rolls over past peak but as the ability to continue to rev, but those are the exception, not the rule.

Just something to think about...

[Motorboy8769]

With stock bottom end and a stock balancer is it safe to spin to 7-7500 during the shift? That’s the only reason I kept it as low as I had it.

[Motorboy8769]

I am shooting for 10’s N/a then probably start looking for a procharger I will be putting the soft lok clutch in this winter when I am back home. Right now the car has a 9” irs 4” aluminum driveshaft headers cam cold air.

[acammer]

Originally Posted by Motorboy8769

With stock bottom end and a stock balancer is it safe to spin to 7-7500 during the shift? That’s the only reason I kept it as low as I had it.

I think 7,000 is very reasonable if you have confidence in the valvetrain. Many guys are sending them deep into the 7400-7800 range. I try to shift mine at 7300. Heads and pan have never been off, just cam and good valve train. I bet you'd pick up a few mph.