Hi folks,
Looks like there is a lot more traffic over here than at rennlist for engine build specifics. I'm doing a straight-forward top end on a late 1991 3.6L. Reasons to open it up were exhaust valve guide leaks and a gasket reseal.
Anyway, I just took a close look at the heads that I had reconditioned and found a crack along the valve guide boss. Found this on two cylinders. Pic shows the worse one. The crack in the other head is very very slight:
What I've turned up on the web:
- One fellow who ran an engine like this and a large chunk of the boss broke off.
- Competition Engineer website lists "Repair crack in port at valve guide boss $215" as one of their services.
- Supertec not concerned about it, they also grind off the whole boss when doing a race port.
So options seem to be 1) Ignore and run as-is, 2) have it repaired/welded 3) an excuse for some fancy port work.
I was also surprised to find the exhaust valve seat is not blended into the port at all. Porsche seemed to think that this wasn't important? I can see a good 1mm+ step on almost all of the heads. Is it worth spending the time to blend these into the rest of the port? The intake seats look great and are completely smooth to the rest of the port. You can see the step pretty clearly in the photo-
Appreciate any feedback. More details in the RL thread:
I'm in the motor now - Rennlist Discussion Forums