Over-rev, how long until you notice any damage?

I have to agree with posters that mentioned valve float. Although more likely with a push rod engine that an OHC one it can cause a bent valve that may not be obvious but will reduce power to some degree.

My on track over rev story goes like this. I was Road America for a HPDE and driving my V8 Mustang race car for the first time that year. I missed 2-3 up shifts from 3rd to 4th and over reved the engine each time. The engine continued to run fine until the last session of the day. While upshifting from 3 to 4th between turns 7 & 8 I heard a "bad noise" come from the engine compartment followed by silence!

A few days later I pulled the heads and found that some of the intake valves had contacted pistons with one of the valve heads breaking off and being pounded between the cylinder head and said piston. The damage was not total as I just put the original cast iron GT40 heads back on, replaced the piston & rod and I had a running engine again. I even took it back on track without further issues.

rcutclif wrote:

Knurled wrote: Rotaries have a "nice" failure mode when overrevving. It's like the five point palm exploding heart technique. Overrev a 3mm seal engine and everything is okay until the first time you take it up to 6200rpm, then it FODs itself. BTDT three times.

I'm glad you added that. As I was clicking on this thread I thought to myself - "I wonder if you can over-rev a rotary..."

Oh my yes The 3mm seals do not tolerate going over 8500rpm ever and really don't like being over 6200. Yes, the redlines were 7k on 3mm seal engines. Notice they didn't actually make power there.

You can also hurt the bearings, or hurt the stationary gears on 85-earlier models, or kiss the rotors to the sides if you haven't added additional clearance.

The only missed shift I have done was in my FC RX7 on the track. I Went from 5th the 2nd. I have no idea how many thousands or for that matter tens of thousands of RPMs I spun it to. The motor finished the day with out issue but once it completely cooled overnight it was apparent I had damaged it.

In your case I would take it easy for a while and see. No guarantees but the longer you go the less likely you did serious damage. I will say that you probably shortened its life some.

Watch out for snapping valve springs in a few days. At least thats what happens on Rover V8s soon after the throttle cable melts against the headers and it takes a few seconds to shut the engine off. Been there....done that.... wait for it... twice.

Only one real story. 2nd real car, 1985 VW Gti. Showing off for some friends. Grabbed 2nd from 3rd slowing for an exit curve. In my youthful exuberance, I was still way too far up the rev range to grab 2nd. Tach spun off the top. Calculated it later from what I could estimate was the speed I was at when I did it. Had to rev to at least 7500. I was on the brakes hard too so it didn't stay there long, but I drove that car another couple years or so and had no adverse affects in that time. I think it really depends on the motor in question. IME VW 8v's are tough SOBs.

My Talon has had probably 4 or 5 3rd to 2nd gear misshifts with some heavy boost. I'd always be quick to catch, but its still instantly very high rpms. Never had an issue.

Oh, that reminds me of another high-rev issue I once had. This was back when my wife and I were dating, and we'd driven down to Atlanta in her 87 2.3L Mustang. On the way back, after about 10 hours behind the wheel, I was accelerating onto the freeway from an on-ramp when the throttle hung on me. Since it kept accelerating, I pushed in the clutch to slow down. The tach went all the way around, 360 degrees, and when I shut the engine off, it stopped at 0 again. I kicked the pedal a few times and it came loose, it was caught in the floor mat. Bump-started it as we were coasting down, and it was fine for 2 more years.

I say do a compression check just to make sure the valves are ok. If so, change the timing belt and carry on.

And reading all the post here reminds me of another over rev story. This one didn't happen to me but I did get to watch it happen. It was at the start of a race that I was in. A car (VW Rabbit)2-3 rows ahead of me missed a shift big time. The clutch/flywheel assembly exploded so violently that the pieces went in all directions. I saw parts flying and then I heard things bounce off the bottom of my car as I drove over what pieces fell to the pavement. After the race I went to look at the results; the hood had a huge upward bulge in it, the radiator was almost cut in half, the firewall had huge dents in it, the transaxle was no longer connected to the engine as the bell housing was shattered into pieces. Oil and water covered everything under the hood. It looked like a hand grenade went off under the hood.

In reply to RyanW:

4G63's seem to be very tolerant of over-revs. I had a couple minor ones (kicked the clutch back in by 8k or so.) One friend in a 2G Eclipse shifted from the top of 3rd into second on the drag strip. The engine spun hard enough to throw the power steering belt. We found it at the end of the track at the end of the night, put it back on, and the car was fine. Another had a 1G Talon at a track day. Missed the same shift. The data logger read 9999 rpm, as high as it could read. The car was fine. I think it's that the stock motors have very strong rods and mild cams.

We over-revved the Datstang (Datsun L28) numerous times due to a limp-noodle shift lever that went into first several times instead of third. Eventually we broke the driveshaft. Welded it back up and kept running. The engine didn't seem to miss a beat.

No clue how much we over-revved because the car has no gauges.

I once hit first instead of third coming out of turn 3 in Calgary. Twice. I was sure I'd jammed the tach, because it was against the wrong side of the stop for quite a while.

Still running.

Did you do the math? Shifted out of 3rd and XXXX rpm & into 2nd and XXXX-100 rpm. get your gear ratios and figger it out. Might not be so bad after all.

Nick_Comstock wrote: My first auto x ever in my E21 I over revved the engine. It wasn't a downshift but I was unfamiliar with the car and at the end of an open slalom section I glanced down and saw the needle at about 7800 and climbing. Redline was 6500 IIRC. It had 275k on it and I never had any issues with it after that.

The M10 is the engine equivalent of the honey badger, they'll rev until they run out of air or fuel, and if you do get rod knock, it'll still outlive a 350 sbc.

In reply to yamaha:

Didn't BMW use junkyard M10 blocks to build turbo F1 engines?

the only severe damage ive ever done from over revving an engine was in a 22r powered Toyota pick up. throttle return spring broke and it stuck too the floor between the 2-3 shift. bent an intake valve, broke a valve seat and spit out a headgasket. it was obvious right away! my marquis seen accidental valve float twice and it was never an issue and that was a car that was abused often.

Kenny_McCormic wrote: In reply to yamaha: Didn't BMW use junkyard M10 blocks to build turbo F1 engines?

Yes, and for good reason. Iron can and will twang after being cast, sometimes for months after machining, and the heat cycling from road use will help relieve the residual stresses and allow the iron to shift around until it finds its happy spot. The BMW engineers found that "seasoned" blocks would hold up better and make more power than otherwise identical new blocks.

It's the same as brake rotors that warp after a few good heat cycles, then you re-machine them and they stay true for the rest of their lives. Iron can be a goofy material.

I revved the Datsun till it floated the valves about 6 laps in a row,exiting turn 1 at LVMS, attempting to catch a competitor. While the motor is non interference fit revving the poor little push rod A-series to 9100 rpms wasn't a good idea.......the next day in the challenge race it made it three laps before the valve lash adjuster screw backed off....if I'd pulled off right away I could have made it thorough the weekend by simply threading the screw back in, instead a the push rod hung up and bam bent valve. After pulling the head I noticed all 4 pistons had tiny circular indentations that seemed to line up with the exhaust valves. Other than the one bent valve the rest of the valves were actually sealing......it's amazing what some motors will tolerate.

 Tom