redline/peak H.P/ & H.P curve-When to shift?? :) intresting???

andre12031948

The 350z site is having a discussion on this. I found my answer years ago just by using common sense. They are having a problem with this subject.

You can have mods but if you shift at the wrong rpm, all those mods will not give you all they can.

Hint-highest/peak H.P. rpm.- redline-H.P./turq. rear gear ratio-and trans. gear ration. I think that's it.

I don't bother with a calculator to get exact, just a quick estimation works fine.

So when to shift to get the best acceleration??? using the hint stuff, maybe other stuff.

At some point I'll tell you what I know/think. Can't hurt you, only help.

DEpointfive0

You should shift at the absolute highest RPM you can. Any lower and when you pick up the next gear, you aren't making the power you could have otherwise

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andre12031948

What if your car can rev to 9,000 rpm but highest H.P. is made at 7,000 rpm.
Shift at 9,000rpm?????

DEpointfive0

Plenty of people here have limiters at 8000, no extra power is made at 8000, but they do it so they can keep more power on in the next gear

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andre12031948

You kind off got it but it's a bit more complicated when you use trans. gear ratios, H.P curve, top H.P. & highest redline. Like what if you make highest H.P. between 6k & 7k & you have your redline/peak rpm set at 9k.?

You were to fast

or what if they shift at the 8k rpm that you said & top H.P is at 6,500 rpm & the drop from gear to gear is from the 8k rpm shifting to 6,500 rpm. Is that ok???

clintfocus

really depends on the situation and what kind of racing you are doing

DarkJak

Unless your power drops off somewhere like 20-30% after peak, it'd be best to stay in as low a gear as possible since the lower gear ratio will put down more torque.

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andre12031948

I guess I should have said going 1/4 & using 4 gears. Sorry. The first person DEpoint50 got it real close & very quickly. The only thing I had a problem with was "absolute highest RPM you can". That is not the case, but he does understand the drop of rpm after every shift. I'll give my answer on Monday. If anyone cares The other forum had a lot of problem with these basic stuff. So what's the point of spending thousand to mod a car for going quickly when one doesn't understand basic stuff like when to shift & why.

andre12031948

As we all know, after shifting the rpm drops. In order to get the max benefit, we need to keep the car's highest h.p the longest time in that drop. Example, if your highest h.p is at 7,000rpm then starts to drop, & because of your gearing(trans. & rear) it drops 2,000 rpm. You draw/pick a line from the dropped side & draw it to the other side (horizontal) where it starts getting going up to the highest h.p. Of course it should cover only 2,000rpm. You should now have THE MOST h.p the car makes in that 2,000 rpm space.

So highest h.p is at 7,000 rpm, shifting at 8,000 rpm & it drops to 6,000 rpm might do the trick. The reason I say might is because the h.p curve on the dyno chart might show that that will not have the most h.p in that range.

That is why I prefer a set up & tune that shows a long flat h.p. peak than a quick going up, then a quick drop. I'd prefer even lower top h.p if the top h.p stays longer(flat curve) but last longer!

Almost 3 years ago I made a youtube video of my shifting, where it clearly shows the drop. Just put my name andre12031948 & click.

Of course one should always consider the safety of shifting at high rpm. 07/08 HR's like mine, shifting at 7,500-7,600rpm is fine, I believe the 370 engine can be shifted safely at 8,000 rpm.

Oh yes, getting gears like 4:08's makes the drop smaller & brings the rpm back up much quicker. Result much more kick in the azz on the street & muck quicker times. My youtube video was made before I started heating my tires in water & had my 3:90 gears, not my 4:08's.

synolimit

My subi had flat foot shifting. That plays too since shifts are lightning fast and rpms stay way higher then if you just shifted normal.

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andre12031948

I just read my post & can see that what I wrote can be confusing to many people. Just pick/mark 2,000rpm(the drop) & put the peak h.p rpm(7,000rpm) someplace in the middle of that 2k drop where the,,,, oh, never mind. Seems I can't explain it clearly

Zbrah

lol jk i get what you're saying. Good read and thx!

GSS138

I'll agree with Clint. If you are drag racing I would say shift at whatever point the next gear will put you closest to you peak torque. If you are road racing, you don't always want peak torque after a shift. Most times you want some engine braking and enough torque to exit safely, accurately, and wo throwing your butt out. In a straight line when you are not looking at your gauges(which you shouldn't be), just shift close to peak RPM. Debating wether you shift at 7800 RPM or 8000 RPM is pretty stupid and a unless you are racing a car some sponsors bought for you, I really doubt you can tell the difference between 200 RPM when you are going 90 MPH.

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Apollo8642

In my opinion and this is sure fire way to figure this out. Take your car to a dyno, get a few pulls in, then check your torque, horse power curves and where they start and drop, that will help tell you where you need to shift. You can even data log shifts on a dyno so you can see what your power does in a down and up shift.

I usuall shift around 6500 rpms plus or minus for whatever I might be doing, my stock clutch likes to cook when I shift at red line. (swapping to a South Bend stage 3 setup very soon)

Here is a dyno sheet from Z1 Motorsports with uprev, and off this I would shift around 6800 to 6900 rpms but you should get your own results with your car, also view it with smoothing off might help out as well.

andre12031948

When I drive on the street I shift between 2k & 3k max. When I drag race or would try my hand on a road track with curves & straight ways, or even a country road I drive this way.
Accelerating at the drag strip, according to this chart, which stops at 7.5 rpm, I would shift(power) at apx. 8k. so when it drops, it ends up someplace where the H.P is going up toward the peak. Same if I was on a straight way of a road track. Turq. is only a concern when I accelerate from a dead start, a slow roll, or after down shifting on a turn then accelerating. After I'm moving at a drag strip or a straight way of a road, I only pay attention at rpm to be at max H.P in the gear drop. When I'm moving, h.p. h.p. hp. is all I care about.

Actually, this chart shows me that it could use 4:08 gears or maybe shifting above 8k. My tune/chart has a long flat line from 6k to 7.5k.