Hitting Rev Limiter

I did not take 996 on the track yet (shame, I know) but drive it somewhat hard on the street. When going on the fun rides to some mountain empty roads in my area on the exits from 2-nd gear hairpins I cannot help but hit rev limiter frequently. Does it happen a lot to to you guys who take it to the track? Do you think it is not healthy for the engine? By the way just today I just glanced on the rev counter and the needle hit halfway into red, 7500RPM for split second while being cut off. Now I have a choice of taking the turn in 3-rd and be bored, upshift while just about hitting the exit (horror?) or keep on what I am doing so far. Advice please?

Down shifting into hitting rev limiter is worse than powering into it. Blowing a head gasket is the main concern I'd have. Also the best torque and power option for turns is below red line. Then you have options for power up and down. Redline in turns will be acting smoother like power curves that are linear but that just deceptive making turns in red line seem better. At least thats my story and I'm sticking to it.

let me ask you a question, are you an old chevy 350 guy? I am... Had my share of vettes and yes I bounce off the limiter more than I will ever admit. I feel it is due to the way the Porsche engine pulls all the way to the limit... Where the old chebby 350 would lose substantial power 250 rpm before its whole ( I think) 4500 red line. So you could feel it in the seat of your pants when it was time to pull the next gear. Where these little porsche engines pull all the way to red line and want to blast though it like a jet to the sound barrier.

Oh.. IMO as long as you are not downshifting and forcing it over the limit I think you are ok.. Thats why the limter is there.....

The rev limiter is doing its job.....and yet, learning to get your timing and cues for shifting right so you're shifting close to red line, but without using the limiter -- is still better. If nothing else, you're slower on the track if you wait for your engine to get into the limiter, then shift.

I's hit it!

Cornering speed is not relative to what gear you are in or RPMs. It's normal to associate high RPM to high cornering speeds, but they have little to do with each other. Stay in a higher gear and you will find that you will be able to go faster. You won't be bored if you study the turns carefully and pick reference points for braking, initiating a turn, etc. It's easier to learn to be smooth without worrying about a screaming motor at redline. Smoothness will get you thru the turns quickest.

nic49 is making a good point. If you're running out of rev's either in the turn or just after the apex, you should have been in a higher gear, anyway.

Thanks for interesting comments. Yes, its hard to sense any power dip just before the redline on this engine. I will enter these turns in 3-rd now and see what happens. I hate hitting limiter just after apex.

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This is incorrect, and make no sense what-so-ever. The rev limiter does NOT protect the engine on a down shift, nor is a spin situation.

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To answer your question: I rarely if ever bounce off the limiter during DE's. Nic is right on with his comment in my experience. You should be more concerned with being smooth and fast than what rpm you're at. Entering the turn in a higher gear/lower rpm may actually help you be smoother coming out of the turn by making the throttle less sensitive. During my last DE my car was running a bit hot so my instructor had me experiment with shifting earlier than I might normally. It was surprising to me that I was essentially just as fast in the higher gears. I was driving more smoothly and the car experienced less wear and tear.

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Both statements are saying the same thing, although in different ways. Basically, type 1 over revs are OK (accelerating up to the rev limiter) while type 2 over revs are considered BAD (downshifting and exceeding max allowable revs) and can be catastrophic. The car logs the count of both occurrences.

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IMO it is both correct and makes sense. Put another way, mechanically over revving the engine can be catastrophic (think shifting from 140 mph in 5th gear to 2nd gear). Running up to 8200 under gas Is no issue. I do it all the time. Sometimes I just bounce off 8200 on certain straights instead of a short up-shift and then a down-shift -td

how fast are you going on these public roads? 7500, 2nd gear is what 65/70mph? and then you are accelerating? sounds pretty irresponsible , if you ask me. just the thing that does nothing to help the image of what the public has of p-car owners. save the speed for the track.

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give it a rest. Mr. Brady. You better call the feds.. I heard he cuts the tags off his matteresses and Sings in the shower. (that by the way is actually illeagle..) Bj's are also against the law.. How many Have u turned down?

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who let this guy into the thread?

Then there are the guy's going up an on ramp at 45mph in 996/997 and everyone backed up behind him in Civic's and Yoda's gonin, 'Who allowed this guy a Porsche - he should have bought a smart car...'

Keep in mind that peak power is reached before you get above 6500 rpm, so to push the engine up there is actually not doing to anything as far as power production is concerned. But when you do run it up higher, it helps you to stay at a higher level of rpms after the shift--the engine would not drop as much as it would if you shifted early of course and wound up with the engine down at 3500 or so--you want the engine around 4500 after the shift to maintain power and torque. The problem with these engines is that they are very free revving engines. When you shift at 7200 rpm the momentum of all that engine mass causes the engine to actually go to 7500. Not a great thing when your redline is what,--7200 or 7300? Enjoy! I am not timid, either!

Doesn't revving the engine up higher when shifting only happen if you let off the gas slightly after pushing in the clutch? Momentum cannot make objects accelerate, it keeps them from accelerating.

Technically that's not accurate, the phenomenon of an object in acceleration remaining such even after accelerative force is removed is accurate, though not quite as pronounced as Dan's suggesting. There's a buffer between fuel cut RPM and the stage 2 over-rev registration in the DME. I want to say the difference is around 100rpm, but I don't recall exactly. In any case, you're not going to log any stage 2 over-revs without mis shifting into the wrong gear (or releasing the clutch early when braking/downshifting on track), and that's really the only way to do mechanical damage to the engine from over revving.

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F = m * a. If there's no force, there's no acceleration. I would be interested in seeing the phenomenon you are referring to in legitimate scientific print somewhere if you can find it. Nobody debates Newton's second law....

I may be wrong with that post, and I didn't quite say what I wanted to anyway, so bear with me. Here's what I meant: When the force is removed, acceleration will slow down, but absolute RPMs will rise somewhat above that point. If we still disagree, I'll try to dig something up. I think the disconnect is caused by the vagueness of the word "acceleration" in this context. That or the fact that it's 3am.

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I did not say the rev limiter protects the engine during downshifts which explains why it makes no sense to think I said so. Sooooo OK. In case you are saying downshifting into a revlimiter situation is the same as accelerating into one then I think that's wrong mostly because it isn't that way and never will be RPM limits made easy with red meaning stop when it should be a sign like $16,000 in red is when you run a chance of engine failure. The cams cut along with the springs and valves are going to approach floating and the crank with rod and pistons could take a hike through the sylinder walls. Increasing rpms upwards with a load on the engine will not have a tramatic rpm change compaired to downshifting into a rev limiter state of affairs. There is some major banging going on in the cylinders at high rpms. The downshifting into redline is more of a hit on the engine thus a better chance of blowing a gasket.

I think there's a clue in the fact that your ECU stores overrev conditions, and distinguishes between hitting the limiter while accelerating (Type 1) and hitting it because of a downshift, a so-called mechanical overrev (Type 2). When they're adjudicating warranty issues, for example, the first kind is usually overlooked, but the second kind is not. I would never, ever mechanically overrev an engine. A smooth downshift into the meat of the torque curve on this car shouldn't require risking it. My .02...

Interesting discussion... Let me mention that even if you see 7500RPM on the gauge for a split second (how I did) that does not mean that your engine is revving that high in reality. I am sure gauge reads always somewhat high in a similar way like on my other cars and motorcycles. On my track bike by the way I can easily change the gearing by changing the sprocket for the very purpose of not having to hit rev limiter on the important turn at the particular track. Can't be done on Porsche so I will see how it goes if I stay in 3-rd for the turn..

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The engine accelerating is angular acceleration. Angular acceleration occurs when the engine RPM is increased OR decreased. The car accelerating on a straight road is straight line acceleration. Releasing the gas pedal is effectively removing the force that is acting on the engine to turn it. (expanding gasses in the cylinder). I suspect the observed split second the engine raises in rpm is caused from the load being taken off the engine by pushing in the clutch, and a small amount of unburnt fuel in the cylinders that has just enough energy left to raise the rpms with the clutch in. It may also be because the operator pushed in the clutch before completely letting off the gas. Try this: get up to 60mph, and some gear that sets the engine at a high rpm. Let off the gas, and let the engine slow the car for 3 seconds. Then quickly push in the clutch. You won't see the engine rpm rise the split second you push in the clutch. It will only drop.

I'm only interested in the theory behind it, I have very little interest in over revving a modern fuel injected engine by hitting redline then pushing the clutch in, as I don't see that as a practical possibility. If I can gather the cognitive ability, I'll send you a PM.

We must be talking about different things. I'm lost.