Konstantin

I had 235/40 265/35
now 225/40 285/30 Michelin sport
on the pic the tires were 16 Inch magnesium telfon design wheels

KOnstantin

pk951

Just a thought at 167.8 miles per hour you're traveling at 246 feet per second how long does it take to stop for a deer? Had it up to 260-km per hour still pulling, no speeding tickets yet in last four years. I think i will stick to the track much more safer.

toddk911

What would need to be done to the motor to handle a higher rev limit?? Lightned flywheel??? Or is there room there with out many mods for the motor to handle a higher rev limit??

Are chips the only way to raise rev limit?

Also, what is difference in hitting rev limit and fuel cut??? I know what the two FEEL like, but...

ninefiveone

rev limit and fuel cut are terms generally used interchangeably and describe the most rpm a set of chips or other form of engine management will allow the motor to run.. That rev limit is generally set to some number less than the actual max the motor can turn without damage. Most chips implement a fuel cut to enforce the rev limit but might also use it for overboost conditions and other issues.



The "actual" rev limit of the motor (i.e. the most rpm it can actually turn without damaging itself) is determine by a number of things depending on the motor.

For 944's it is usually the valvetrain which is the limiting factor. As the revs reach a certain point, the valvetrain will begin to experience float which basically means the motor (and camshaft) are now turning so fast that the valves no longer close and open properly. Inertia of the valves themselves, the spring rate of the valvesprings, the type of lifters that the 944 uses all play a part in that.

toddk911

So all of those that have psoted about 6,500+ rev limits had some sort of head/valve work done to handle those revs???

TRWright

I rev to 6850 in 4th, but not yet in fifth. (stock head/valves/springs) I would imagine that it is not so great for the engine with so much load on it at those revs.

toddk911

What is the stock rev limit at?

Anyone know what GURU chips rev limit is at?

ninefiveone

Stock rev limit is set at 6400 I believe. Guru is set at 7000 I think.

Based on what I've seen on this board, valve float doesn't seem to be an issue until somewhere around 7000rpms and up. We are talking about the rev limits for motors in varying states of condition, though, so that doesn't mean it isn't lower or higher for your own car.

There is also a big difference between revving to 7000 in neutral with no real load on the motor and valvetrain, and doing it in 4th or 5th. Doesn't take much fuel (and hence combustion pressures are a lot lower) to rev to 7000 in neutral or even as overrun when you're shifting from 1-2. But it does in 4th or 5th.

The rest of the 951 motor isn't optimized for high rpms either. The intake manifold isn't optimal for high revs (not that it won't work but it's tuned for low-mid range torque), nor is the camshaft. None of those things limits the revs you can turn but they make it less worthwhile. But plenty of people (hojpefully including me in a week or two) can bolt on a bigger, better turbo and make plenty of power at high revs without changing either the cam or intake.

Frank@Work

The rev limit for my Guru chips is definately not at 7000 rpm! I think Danno forgot somehow to change the rev limit to 7000 rpm.

It doesn't matter for me, because I normally shift at 6000 rpm.

ninefiveone

What's it at?

rage2

I generally stick to the track. Top speed runs, you need a lot more straight than most tracks have to offer!

Frank@Work

Stock! I think somewhere around 6400 rpm.

DFASTEST951

I have 265/35/18 SO2's on Kenisis Motorsport Polished Supercups. At 194mph, I was below 7000 rpm. Like 6800 or6900 (tried not to look too long). As far as rev limiters, I don't know what mines at. Powerhaus just told me a top speed run with the car won't hurt it. So I did it. No deer in Las Vegas...