Mechanical overrev - how bad? Next steps?
10-23-2015, 09:11 PM
#16
Rennlist Member
Thread Starter
To be fair, I never found the GR as precise as everyone raves about. As Steve suggestested I will check the linkage to be sure.
Cheers
Matt
10-23-2015, 09:16 PM
#17
Rennlist Member
Thread Starter
I had the same misfortune years ago. I completed the rest of my lap (under less power - I knew I had done a bad thing ) and car stopped in the pits for good. End result was two broken rocker arms and many bent valves, hence $ shift indeed.
IMO, the fact that you made it home is amazing. Did you notice any loss of perceived power, any new engine sounds after the event?
Hopefully you were lucky and no damage was done.
IMO, the fact that you made it home is amazing. Did you notice any loss of perceived power, any new engine sounds after the event?
Hopefully you were lucky and no damage was done.
Won't know what's what until the leakdown is performed... we'll see. Hoping for the best.
10-23-2015, 09:33 PM
#18
Perhaps you lucked out then. Certainly a nice, old school track, to do it at.....at least there's that. Good luck on your findings. I think we've all in the heat of battle dropped a gear, lightened the foot off the clutch and heard the start of something bad happening....immediately depressing the clutch once more and grab the proper gear. Cheers
10-23-2015, 09:39 PM
#19
Rennlist Member
Matt,
So sorry to hear about The Shift. Hope it turns out to be no big deal. One of the reasons I bought a 993 was too avoid tracking a 915 tranny with all of its inherent vagueness. I mis-shifted my 3.2 Carrera at my first ever DE (Putnam Park). I had never mis-shifted a car in about twenty years and promptly sold the 3.2 to wheel a 993 with the better G50 box.
So sorry to hear about The Shift. Hope it turns out to be no big deal. One of the reasons I bought a 993 was too avoid tracking a 915 tranny with all of its inherent vagueness. I mis-shifted my 3.2 Carrera at my first ever DE (Putnam Park). I had never mis-shifted a car in about twenty years and promptly sold the 3.2 to wheel a 993 with the better G50 box.
10-24-2015, 08:30 AM
#20
Pro
Anything can be overrevved, even race engines.
Remember, racing engines have a LOT of custom & non-standard parts in them that are specifically designed to withstand extended high-RPM use including an occasional slip up. Street engines are not so forgiving.
Remember, racing engines have a LOT of custom & non-standard parts in them that are specifically designed to withstand extended high-RPM use including an occasional slip up. Street engines are not so forgiving.
Steve,
thanks for your reply.
Believe me, I'm fully aware of this. Now. After the damage was done.
Never hit the rev limiter in first gear (which I did). I always was under the impression that the rev limiter would prevent any engine damage under, well, "normal" driving conditions - not racing the car and selecting the wrong gear by mistake.
Other's might still not know this. In particular in combination with worn valve guides, which is a flaw in the 993 engine design. Correct?
10-24-2015, 10:49 AM
#21
The only way a car could prevent an over rev downshift is if it had a mechanism that would prevent the shift from occurring at all. Once the drive wheels are attached mechanically to the engine via the tranny, the engine will do whatever RPM is necessary.....the only slippage built into the system is the clutch and once that's fully engaged....
10-24-2015, 01:31 PM
#22
RL Technical Advisor
Further, guide wear is not a factor in possible valve damage when the engine is accidently over revved. That is due to valve float which are valves hanging open when the springs fail to control their inertia at high RPM. Its important to remember that valve springs do suffer some fatigue over time allowing the threshold of valve float to go lower as the engine accumulates miles.
We always test valve spring pressures when the heads are rebuilt and replace the springs if/when they are at minimum spec. The higher the peak revs during engine operation, the more diligence is required in this regard.