joshbot007

So I was out doing some pulls and for whatever reason I accidentally went from a winded up third to second. This showed 8,692rpm on the log. I felt like **** as soon as it happened and the clutch was pressed immediately, but despite my efforts the surge or high rpm was enough to pop off the power steering belt. The engine seems to be running fine with no weird ticks or taps, still pulls strong, and no loss of fluids. Basically everything appears normal. The motor is bone stock with a fm2 kit with some differences. My question is what does a short (unsustained) miss-shift to this high of rpm do to a motor or what could I of expected to damage if anything? Oil pump? valves? rods? People who have done something similar what have you found or how does your motor seem over time? I figured this was the best location for a post like this as its all engine related and I could not find a similar post with high rpm (or at least the evidence to back it like a log) like such.

Ryan_G

iTrader: (8)

No one is going to be able to give you a definitive answer without opening the engine and looking at the rods. They may be completely fine. They might be slightly warped or weakend but not enough to cause noticeable issues. If you are not noticing anything wrong I would just keep driving it. It's usually fairly obvious when you have damaged an internal peice enough to break the motor.

For instance, I missed a shift from 5th and hit 2nd instead of 4th. I think I hit something like 13k rpms. My rod was pretty vocal that it was not pleased. It then decided it was sick of my abuse and it was time to exit the motor.

Lexzar

iTrader: (2)

If it isn't dead after a true 8600rpm, time to turn it up to 300whp.

Run it as is until it dies, and don't do it again?

codrus

From what I understand, it's not too unusual for an overrev like that can weaken a rod such that it will fail a few weeks or months later. That said, there's not really a lot you can do at this point, there's no way to fix the rod other than to replace it, so you're balancing the cost of rebuilding a currently-working engine vs the cost of rebuilding a broken-rod-hole-in-the-block engine. The latter is slightly more expensive (because you need a new block and probably a new head), but the block and head you have now are stock, so they're not particularly valuable. That equation might change if you had a $3000 949 CNC head on the engine. It also might change if you're concerned about it blowing up at an unexpected time, incurring inconvenience and cost from having it towed/etc.

You could check for a bent rod by carefully measuring the height of all four pistons relative to the valve cover at TDC and comparing them, but it probably wouldn't tell you much.

--Ian

joshbot007

yea I get that. I was just trying to get a feel of what kind of stuff goes out when this happens so I can keep an eye on those things, Thanks for sharing your experience as other peoples experiences are really only what I have to go by.

Erat

iTrader: (5)

I've done it twice(once i was already rung out to around 7700rpm). But my motor is completely built, no issues yet.
I do however believe other components in my drive line were hurt, though they didn't immediately fail.

I really hate to do it again because i believe the 3rd time to be the charm.

Savington

iTrader: (31)

Yep. Might fail tomorrow, might fail in 3 weeks, might fail in a few months, might never fail. No way for anyone here to definitively tell you when it will be. Plan accordingly.

Arca_ex

iTrader: (2)

I once went from third to second on track when my stock motor mounts failed. It was exiting a corner and when I let off to shift, the engine/trans flopped back over and lined up second for me even though I pulled straight rearwards to what I thought was fourth. Hit nearly 9 grand as well.

That was probably three or four years ago and the car has done hundreds of hours of racing since then and about 10k street miles, no issues. Like others have said, your mileage may vary, hope for the best, prepare for the worst.

DaWaN

Also had it once with my old Daihatsu Charade with HC-E engine. That engine has a very similar 7000 rpm redline as the Mazda BP.
Third to second misshift, hit 9000 rpm too.
Engine did not run anything different and went going until the car got scrapped because of rust years later.

Most likely damage from such an overrev event will be a piston hitting the valves (then it will be the end of the motor instantly) or a bent rod.
If your engine runs fine and does not feel down on power, I think I would not be too worried about it.

unplugged92

iTrader: (1)

I did the same thing in my miata with a turbocharged BPW4. That was 2 summers ago, the engine seems to still be running fine. Although I've never taken it apart to inspect it inside. Only inspection I did was a compression test and all the cylinders tested very close to each other.

If you don't have stiffer engine mounts, I highly suggest you consider upgrading. My shifting was much more precise after going for AWR 70 durometer mounts. I installed poly diff mounts as well.

joshbot007

I have mazda comp mounts. Also, the car is running fine and smooth as always. I am going to forget about it and still go for the tune in February on 12psi. The worst that happens is I end up building a motor about a year early and get even more power But I do hope it lasts on the full power I always planed for it in its stock form. But im not going to let this hold me back im gonna forget it because then the whole point of what i spent time and money for is wasted by not enjoying to full potential.

IcantDo55

iTrader: (11)

I managed a 5th to 2nd shift in our chumpcar, popped out the dipstick splashed out some oil and after the quick fire went out we rolled on for 14 more hours till the rear went.