Missed a shift and over-revved the engine and leak down indicates that I have bent the intake valve on Cylinder #1. So I will need to replace it with something. Should I try to source a factory replacement valve, new or used, or an aftermarket steel valve. At this point, I am not planning on replacing all the valves, so what is my best option for replacing this one valve. Would a good straight used intake valve be acceptible, or is that being too risky? All comments welcome.

Go with a new Porsche valve if available. Talk to George at AA.

Just curious on how bad the over rev was...


Nice chalon by the way.

Might consider waiting until you tear down the motor to inspect and assess the entirity of the damage done. Let us know how that goes & you'll likely get better suggestions on a path forward.

In the meantime, a good suggestion is to invest in a rev limiter (you indicate a missed shift and not a mechanical over-rev from downshifting to the wrong gear). As simple as a special ignition rotor or as complex as an ignition system with a rev limiter.

It happened on the track and might have been 4th to 1st (instead of 3rd) downshift that brought the revs up to around 7K+. Then a loss of around 15-20% power. Rev limiter wouldn't have helped since this was a mechanical over-rev. I'll open it up and assess the damage. And I've learned my lesson and I'll be upgrading my shift linkage to clean up the shifting and hopefully not do this again.

I would suggest a new valve. You never know what you'll get when dealing with used.

Wow, from forth to first, I want your trans, finding first gear on mine is like hunting Grunion.

Concur. If you dinged one, you probably dinged 'em all...

An infamous 4th-to-2nd "upshift" at Lime Rock...After a quick pull and a replacement with some used valves laying about (thanks, Chris!) we were back on track a day later.

(EDIT: Quick calcs of stock gear ratios from 4th to 2nd at around 6000 RPM shift comes to around 11,500-12,000 RPM...so we know the bottom ends are stout...then again, I broke the crankshaft on that engine a few races later, so...?)

Click to view attachment

Pull all valves and inspect. if one hit a piston, more than likely it did the same in other cylinders. Likewise, inspect piston domes for evidence of contact.

Ouch! I hit second a couple times and that was scary but luckily I wasn't at those kinds of rpms. I am always amazed at how easily that transmission will rev and accept that kind of a shift. Many of my old sport cars wouldn't even let the gear mesh with that kind of difference.

This brings back bad memories. I let my buddy drive my 914 and he went from 70 mph in 3rd back down to 2nd when he shifted... Of course he was slow to react and let the clutch out fully and pressed the accelerator to the floor for a couple seconds.