Of course the rotating mass doesn't immediately lose its rotational kinetic energy - I never said it would. But the instant the rev limiter cuts in, that rotational kinetic energy *stops increasing*. Since the rotational kinetic energy is equal to the rotational inertia (which is constant) times the square of the rotational velocity (KE= I times omega squared), that means that when the kinetic energy stops increasing, so does omega (the rotational velocity). That means that once the combustion stops, so does the acceleration of the rotating mass. It keeps moving, of course, but it's not going to *speed up* once combustion stops.

Or here's a slightly shorter way of explaining it -- At the instant the rev limiter kicks in, the rotating assembly has a kinetic energy determined by its rotational inertia (which is a fixed value) and its rotational velocity. The rotational velocity cannot increase any further unless *more* kinetic energy is added to the system. With no more combustion (since the rev limiter has kicked in), where exactly are you claiming that this additional kinetic energy comes from? Look at the formulae and do the math, and you'll find the answer.

Claiming that the kinetic energy that's already present in a rotating system will somehow cause the velocity to increase without any additional energy being added is silly. Because what would happen if the rotational velocity *did* increase, as you're claiming it will? The kinetic energy must then increase, since kinetic energy increases with velocity. Well, since there's even *more* kinetic energy now, the velocity must increase even further, right?, which leads to more kinetic energy, more velocity, more kinetic energy, more velocity, etcetera etcetera. All without any combustion taking place in the cylinders. Congratulations! You've just created a perpetual-motion machine!!

 

Woohoo!!! No more paying for gas!!!!

 

f=ma. a=f/m. a=v^2/r. there is no way we can protect the engine with one oil change every 16K miles!

 

Ok, Ok I'll admit it I was wrong, very wrong, Now lets never speak of it in public again, All kidding aside thanks for the great E-mail it was very informitave. And one more for the record I was wrong.

 

I accidently dropped into 2nd from 6th (instead of 4th) while doing 85mph in my bimmer.

I quicklky realized my (absolutely horrendous) error and put it in neutral. It bounced on the rev limiter and sat there for about 2 seconds, and then normalized.

This was at ~1500 miles. I am now at 19K miles and have had no problem... Good thing it's a lease though, and I don't plan on keeping it in case my 2nd gear fiasco caused damage.

 

Yeah, I had a Saab Turbo about 10 years ago and was accelerating very hard with the stereo on very loud (yes there is a story here, no you can't hear it) and missed 4th, went to 2nd instead.

I didn't know I had missed it and still was on the gas. It took me several seconds to realize I had hit the rev limiter.

I could feel the loss of power and glanced at the tach and it was bouncing up to red line, then falling to almost nothing, then bouncing right back to red line.

I drove it for 50k miles after that before I moved on to something else and never had any trouble. Probably the most reliable car I ever owned.

I wouldn't worry.

 

Thanks Scott. I think he gets it now =)

 

ok what about 3rd at almost redline to 2nd? how badly would that hurt the car? early 04 S lets say.

 

it will not hurt the car.........

 

I was just worried about the valves. there was no smoke and i didnt smell any burning clutch but i just really worry about my car since i love it so much. how high can it run without being hurt?

 

Ouch, I couldn't believe that I did this tonight on highway. I mis-shifted into 2nd gear from 3rd gear around 6000rpm, and I saw the engine was over-reved to 8000k rpm perhaps. I did clutch in the second after I saw the rev bottomed.

Any damage on synchro or engine? I didn't feel anything yet and it was very cold outside.

 

if it doesn't start making bad noises right away your fine.