Is it really necessary to rev to 7900rpm?

[tekmoe]

So I've had my car for about a month now and I've ran it up to redline several times just because that's what she wants me to do. But I've noticed I can feel a slight dip at about 7500rpm. I found a dyno chart for a stock Z4M and I believe this is exactly what I am feeling...



So the question is, do you really need to rev it all the way to redline if there is a dip in the powerband just before you get to it? In the dyno graph, it appears that you almost reach peak power anyway at about 7500rpm.

I would imagine the tunes that are available for this car might resolve this dip. Anyone know?

[O-cha]

Yes, unless hp is falling, there is no reason to shift, even when HP is falling a lot of the time you should not shift.

[pokeybritches]

Originally Posted by tekmoe

I would imagine the tunes that are available for this car might resolve this dip. Anyone know?

Check out the "AA tune - success" thread.

Even if you are making less horsepower at the upper end of the rpm band, you will be faster if you run it to redline because of the torque multiplication factor of your gears.

[tekmoe]

Wow, thanks for the tip, pokey! Those results look awesome! Hard to believe he achieved an increase of 27 hp AT THE REAR WHEELS! Very impressive for a N/A car.

The dip is still there but then it climps even higher after that to redline. I bet his car runs like an animal!

[gatorfast]

Also by shifting at readline you should be right in the heart of the powerband in the next gear.

[krnnerdboy]

Love the AA tune....you really need to stay in for the next gear

[mfanatic325]

Hehe yup, as has been stated, redline is good for maximum acceleration. Moreso to help you stay in a healthy portion of the power band after upshifting, rather than maximum power. Different cars behave slightly differently due to many varying factors such as road conditions, gearing, differential, tranny perhaps, tires, etc. etc. etc.
The list goes on forever. I guess what feels most comfortable to you during time of operation is what matters most.

My car's still feeling pretty good. I've gotten used to the power now though after two track days; one in the wet.

Can't wait for the headers to go in. That'll be at least another 20rwhp ^_^

[lucid]

You need to compare the power output of the engine in the current gear vs. the power output it would have in the other available gears. (Power output will change if you shift because the engine will be operating at a different rotational speed in another gear). If the former is higher, and if you have not hit the redline, you stay in gear. If it is lower, you should shift. Of course, this is assuming you want to maximize acceleration and have traction. In certain cases, it might make sense to hold the gear even if you can make more power in another gear because it takes time to shift. Finally, the engine will respond somewhat differently on the road (compared to sitting on a dyno) due to the dynamic loading and intake conditions, so that dyno plot you are looking at is simply a first order guide, and not entirely representative of what the engine will do on the road.

[tekmoe]

Originally Posted by lucid

You need to compare the power output of the engine in the current gear vs. the power output it would have in the other available gears. (Power output will change if you shift because the engine will be operating at a different rotational speed in another gear). If the former is higher, and if you have not hit the redline, you stay in gear. If it is lower, you should shift. Of course, this is assuming you want to maximize acceleration and have traction. In certain cases, it might make sense to hold the gear even if you can make more power in another gear because it takes time to shift. Finally, the engine will respond somewhat differently on the road (compared to sitting on a dyno) due to the dynamic loading and intake conditions, so that dyno plot you are looking at is simply a first order guide, and not entirely representative of what the engine will do on the road.

Good explanation.

I'm still confident my butt dyno matches up to the dyno graph I posted. I've redlined it several times and I've felt that dip at about 7500rpm each time. Would be nice to flatten that out. Even then though, the car runs great so I can't complain too much.