sjsfiji

All,

I inadvertently went past the redline in 2nd gear where the engine died for a split second before I let off the pedal. Did I damage anything?

Regards,

sjsfiji

911Dave

Nope, the fuel cutoff did its job and saved your engine. Bouncing off the rev limiter is a common pastime among 911 enthusiasts. It is a little jolting, however, and rather alarming if you're not expecting it.

AOW162435

No damage.


Andreas

User 122821

The only way to over-rev these engines is to downshift into a too low gear and engage the clutch. This is know as the "money shift" as in the money it will cost for that mis-shift.

jscott82

If you were in second gear - on the gas and ran into the rev limiter? If so, ya, no big deal at all. Its not the best thing for the motor, but that's what the rev limiter is for.

Now... If you botched a 3-4 shift and caught 2nd instead and over-reved it that way... That's a different ballgame, rev limiter can't help you there.... If the motor sounds fine, you probably are.... If it now has a new ticking sound, you probably want to get it looked at....

Just my 2 cents....

Matt Lane

Funny, when I started out with my first Porsche driving only on the street, I couldn't imagine the need for a rev limiter. How lazy do you have to be to bang off a rev limiter???

Fast forward 16 years, and my driving skills have improved significantly on street and track. And as attuned as I am to what I am doing, trying to be smooth and mechanically sympathetic, it never ceases to amaze me how often I now hit it. With 12-15 track days a summer, I'd be lying if I said it doesn't happen a few times...

Mark in Baltimore

As has been already stated, hitting the rev limiter hasn't broken anything, but it's also not too great for the motor. Best to avoid using it and shift when the tach hits the actual redline.

Reddy Kilowatt

What damage is done to the engine by bouncing off the limiter?

gonzilla

+1.

Basal Skull

Well, the rev limiter is supposed to keep the engine from reving faster than it was designed to do. (limited by valves/springs/oiling etc). So if you stomp on the gas in neutral or do the money shift and shift into 2 when you really wanted to shift into 4th, the engine may turn over too quickly, may get valve float (i.e. the springs aren't strong enough to retract the valves fast enough and the piston head hits the 'floating' valve). This may cause bent valves/problem with guides etc etc. If you're bouncing off the rev limiter as you accelerate at the top of 2nd or 3rd or 4th, you're probably okay. But, the stress on engine components go up exponentially as I understand it with increasing rpms and probably should be avoided. If you shift at optimum rpm, and drive at reasonable rpms, your engine will last a long time. If you keep your engine gunned at redline continuously, you might have maybe 30? hours. (that's why race car engines need rebuilds around those time frames) .... AFAIK

Mike J

One weak spot on these engines are the rod bolts - they are fairly small (smaller than the earlier engines) and can stretch on an over-rev. You are not likely to hit this while hitting the rev-limiter, its usually caused by an over-rev by wrong gear selection and essentially forcing the engine to spin faster than you would get to under power (since the rev-limiter will trigger and cut the power when the redline is hit).

The rod bolts can be damaged when this happens due to the excessive forces (unweighted and weighted) from the weight of the pistons/rods, and since the rod bolts are essentially springs that have been over stretched, they may not go back to exactly the same state as before the over-rev. This means their clamping pressure on the rod bearings is not as high as before since they are now longer, and if excessive, the rod bearings can fail, sometimes thousands of miles after the event. Replacement of the rod bolts is a good thing if a rebuild is underway, suppliers like ARP make bolts that are much stronger and more resilient.

Other things can happen, like the valve can float during an over-rev, and nasty stuff like piston/valve collisions can occur, bending valves. As well, intermediate shaft stresses can cause issues with the oil pump and couplings...well you get the idea. That kind of stuff you usually know about immediately...

However, the really bad stuff is almost always because of a missed shift and a forced over-rev, not due to hitting the rev limiter. But I would avoid hitting the rev limiter repeatedly, its a safety device, not a driving enhancer.... :-)

Cheers,

Mike

gonzilla

I get the damage that can be done by over-rev due to missed shift, but as for bouncing off of the rev limiter... I was under the impression that the redline was rather conservative for this motor. Have I been misled?

Mike J

I have not see any real metrics on this - its all anecdotal to know what the "limit is". Conservative or not, I will go to redline but rarely hit the limiter. Its mostly if I am "busy", say on the track and I am working on steering/braking or track traffic and "forget" what is happening engine wise. Again, its a safety, not a driving aid.

DryFly

Interesting. At what Rpm's (where in the red line zone) does the limiter kick in?

Steve Weiner-Rennsport Systems

Totally agree.

Its tough on the rod bolts when compressive bearing loads are suddenly lifted when the fuel is cut off. The rev limiter is there to save the engine from failure, but not to use it to set the useful power range. Thats why we install shift lights in race & track cars to give the driver a visual reminder to select the next gear.