Thread: Best time

been thinking more about the quarter mile and was wondering...... when is it that u shift.....my sr20ve cams stop making power at 7200rpm and start falling off....which is normal. so when do i shift at 7200rpm or 7500rpm or 8000rpm

This is not VE specific, and would be best answered in the drag racing section.
Do you have a dyno chart for your engine? That would provide the best answer.
If not, assumption would be to shift around 7,500 rpm.

sorry about the post then.... but my dyno shows that after 7200 the power starts to drop off

So you do have a dyno sheet? Can you post it up?
Just because power drops doesn't mean it's not advantageous to rev it past power peak. 99.999% of the time it makes sense to rev past power peak.

^^^^^^^ What he said. You want to shift where you have the best compromise of avg hp and torque multiplication at the wheels.

For instance, find out how far your rpms drop when you shift. Find your peak power, then see what shift point will give you the best avg hp. You could go as far as to consider the torque multiplication by gear, but that isn't really that necessary.

why does the dyno run start so high in the rpm's? shouldn't it start lower at like 3500?

i think there a remote that the guy uses to start the logging of the run and i guess he started it a bit late....

no more input ppl...

Like Coheed said, it's best to find out the rpm spread between shifts.
What I mean is, if you shift at 7.5k rpm does it bring you back down to 6.5k or 6k or maybe even 5.5k?

I'm can't remember the last time I actually paid any attention to my shift points and rpm drop, but I'm going to assume a 2,000 rpm drop just for the sake of argument.

If you shift at 7k rpm you will go back down to 5k rpm. That means you're riding the wave of power from about 120 WHP to about 172 WHP. I'm over simplifying it, but that's an average of 146 WHP.
If you shift at 7.5k rpm you will go back down to 5.5k rpm. That means you're experiencing power from 132 WHP to 170 WHP which is approx. 151 WHP avergage.
If you shift at 7.75k rpm you will go back down to 5.75k rpm. That means you're experiencing power from 150 WHP to 165 WHP which is approx. 157.5 WHP average.

This is terribly general, and is actually quite far off from the real math involving calculus to find the area under the curve. The avergae doesn't even take into account the high power peak between the two numbers.
I could do the real math, but I'm not about to right now. We could do an approximation with polygons instead which I'd rather do. Point being, even the roughest of estimates says you should shift at 7.75k rpm (if you're experiencing an rpm drop of 2k per shift).

I feel like I'm making this overly complicated.

Look at the dyno chart and imagine that you want to shift somewhere past power peak and have the rpm end up below the power peak somewhere. The best you can do is ride the top of this camel hump of power during every shift. Since your hump is quite symmetrical it is easy to decide where to shift to make use of all of your power.

If you had a slow, gradual power build until peak and then it dropped off very quickly you wouldn't want to shift past power peak very much.

If you had a very quick onset of power peak and the power didn't drop off much afterward you'd want to shift well past your power peak to make use of the power you have.

Really, I think the pain killers for my recent surgery are preventing me from putting together a cohesive response. Just ask any questions you have and I'll try to make it clearer.

Really I should make some graphs with photoshop and stuff, but they must be out there on the Internets somewhere already.