Liquid oil in the exhaust.... and other oddities

[maytag]

Originally Posted by 911monty

Still no answer to did the engine spin backwards, but I'm going to say probably.

Sorry, I didn't mean to leave this hanging. the truth is that I don't know. It's quite possible. Everything happened very quickly. This wasn't a slow spin from powering through a corner, that I was trying to save. This was a very fast LOOP, caused by a previously oiled-down corner on the track. The fact that the motor died as a consequence of the spin could suggest that I didn't get the clutch in fast enough, and so yes, it could have turned backwards.
I realize that's an unsatisfactory answer, and probably shows my novice-level at the track... since this was, in point of fact, my FIRST spin (unless you count the day in 2006, when I took one of the school mustangs out in the snow with a Journalist who'd come to see the then-new track facilities, haha). I have to say though, unequivocally, that the spin in the Porsche was far preferable to the equivalent on a motorcycle.

Originally Posted by 911monty

My theory basically is that one cylinder had recently fired but did not get to exhaust valve open. When the piston reversed, the compression ring lost seal on the piston ring-land and dumped as blowby into the crank case. Excess pressure in the crankcase popped the plugs before it could bleed through that long tube to the AOS which had no where to dump due to loss of vacuum in the intake tract when engine quit running. Pressure then relieved through the first weak point. I don't have the dimensions of the plug that popped out but I'd estimate about 3" diameter? Doing the math that puts it ~7 square inches. A cylinder head pressure of only 2 psi would exert 14 lbs of force against that plug.

this all makes sense to me. What we'll hope then, is that I didn't break a ring-land in the process.

I'll try to run a leeakdown test before I start putting things back together.

[911monty]

No problemo. The oil on the track may have caused the spin but it's possible due to the lack of traction may minimized engine reverse rotation, and that's a good thing. When you do assemble and get ready to fire up, even though the AOS may be undamaged, I'd recommend disconnecting the tube and plug the port to the intake. Then take a hose and run the tube to a bucket. No sense in taking unnecessary risk.