Gear Calculations and Rev Limits

daj349

Everywhere I've read on the forum owners regurgitate the statement that power drops after 7 or 7.5k rpm. Yes, it does. But just because you're losing power doesn't mean you're going to make more power when you shift to the next gear. The area under the curve per rev is what is important here and it seems many tuners do not realize this.

We're looking to maximize the integral of the horsepower curve between the gear changes. Also, the drop after the OEM rev limit is going to depend upon your mods and tune. I based my gearing calculations on stock sport tires btw. It's attached to this post.

Let's look at an example of Mike's dyno

N/A HP BRAG thread



(red) Shifting from 2nd to 3rd at 7500 rpm and 338 hp brings us down to 5250 rpm and 270 hp.

(blue) Shifting from 2nd to 3rd at 8k rpm and 325 hp brings us down to about 5550 rpm and 285 hp.



It's clear to see that the average power produced per rev when shifting at 8k rpm is much larger than at 7.5k

When we are reving that high, oil starvation has been the main issue. This is further exasperated by lateral acceleration. Do we have evidence of how this engine holds up at 8k every once in a while? Please post references or first hand experience and not just what you've heard. That's how misinformation occurs. What's a happy medium between 7.5k and 8k? I know we have a wet sump and the the old GTM brand was looking into putting baffles in the oil pan to help. Also do we have more reference N/A dyno graphs going above 7.5k? I've only found 2.

Attached Images

speed calculations.jpg (497.6 KB, 20 views)

__________________
K&N Typhoon | CNT HFC | Berk CBE | Stance True-Types | UpRev

BGTV8

Review Megan370Z build thread for what happens to oiling system over 7500rpm

There is lots of feedback from JWT about sustained rpm over 7500 and standard oil pumps plus cracks in cranks running race engines @ 8800rpm

The problem with saying "occasionally" spinnng to 8000rpm is that no-one knows how long turning the engine that hard results in oil pump gear failure as a consequence of engine harmonics.

There are a couple of track-only or predominantly track cars running over 7500rpm with the OEM oiling system that have extended engine lives .... others have grenaded.

For me, I will go dry-sump before spinning over 7500rpm because I'll have a 30K engine and I have burned cranks and rods in the past buy not engineering the oiling system properly first.

Tread your own path ....

FPenvy

theory works but the engine will grenade if you keep going that high in the RPMs.

you want to do that need the dry sump system as the guy above stated.

but can I play devils advocate.....

so you do 7k (safe) and its 338 to 270 - 68 HP
and then 8k+ (bye bye block) 325 to 285 - 40 HP

the HP gap is less but the danger is up.

go dry sump and you can do it all day lol

__________________
324whp/258wtq AAM Tuned |F.I. NonRes CF CBE/NonRes TestPipes #373|UpRev Tuner|Akuma Motorsports Intakes|Z1 34 Row Oil Cooler

daj349

Thanks for the input. Raising the limiter to 7.7k or 7.8k wouldn't be too extreme though, correct? I just couldn't find much information on people raising it. Megan370z was the only guy I saw that blew one at 8k and I'm assuming most people that run a tune at least raise it a couple hundred. Also, keeping wet sump, having baffles in the pan, and a better pump would probably be an easier solution that converting to dry sump. It's probably not worth doing either though except in extreme builds or for novelty.

__________________
K&N Typhoon | CNT HFC | Berk CBE | Stance True-Types | UpRev

FPenvy

My limiter is at 7900 but I don't take it that high. I raised mine for the purpose of the Power cutout when you get even a little bit close to the stock limiter.

__________________
324whp/258wtq AAM Tuned |F.I. NonRes CF CBE/NonRes TestPipes #373|UpRev Tuner|Akuma Motorsports Intakes|Z1 34 Row Oil Cooler

ANMVQ

Agree with FPenvy, I have mine set at 7800 RPMS, don't go there either I shift right @7500, try to anyways

__________________
14 Q50 AWD, ARK, ECUTEK (SEB), Takda,

FPenvy

Based on my dyno sheets I peaked power at 7350/7450 area so that's my ideal shift point.

__________________
324whp/258wtq AAM Tuned |F.I. NonRes CF CBE/NonRes TestPipes #373|UpRev Tuner|Akuma Motorsports Intakes|Z1 34 Row Oil Cooler

Rusty

My limiter is set at 7,800 rpms. My shift light is set at 7000 rpms. Soon as the comes on. I shift. Between me seeing the light come on, and me shifting. The tach is around 7,500~7,600 rpms.

__________________

浪人 - 殺し屋
"The Difficult Anytime, The Impossible By Appointment Only"
http://www.the370z.com/members-370z-...o-journal.html

Elmo370z

1slow370z had a 8200 rev limit, but he had a dry sump, and proper supporting mods to support the air flow