[xwcgt]

Ill make a long story short , just for those that might have had an overheat issue while driving spirited , or at the track.

the 928 engine is very sensitive to water level. as some would say, its self birping and for the most part it is, but technically it isnt. you start getting to the higher temps of the engine coolant and if you have air pockets they can become worse due to boiling that pushes water out and then is not replace when the steam condenses and the engine cools.
i was in a race and have raced the race car at temps as high as 110 degrees, pushing 370+ rear wheel hp all race long, without any overheating issues what so ever. so why did i overheat? had air in the system, usually that is burped out , with the overflow filled to near the top (1" or so lower than top) . it must have pushed fluid out of the over flow, then cooled on cool down laps but was still over heated but no pressure in the lines , in fact, a slight vacuum. the system was low on water and wouldnt "self burp" even though coolant level was normal. this is because contrary to some guys on the rennlist's belief, the over flow is the highest point in the circuit.. which it is not. in fact the water bridge is a full 2" higher than the lowest point of the water container. so, there is the smoking gun.
the top hose of the water bridge can be a source of air as it attaches to the top of the container and the other one at the bottom goes to the top of the radiator.

(as a note, i have modifications that i dont use, but were installed by porsche NA or the factory for bleeder ports on the water bridge ,so someone else must have thought there was an issue too)

so, the reservoir has got to be more than half full, or you could have an issue on a very hot day.

I checked (due to most of the suggestions)
water pump
(actually removed it because there was a slight bearing sound,but it turned out to be a Gebe pump that had a high spot on the impeller that was hitting the block with no real damage . impeller was secure and not moving. replaced with new Laso pump)
checked all plugs......normal
compression check.......... 190 to 200 psi in all holes.
and after a refil and burp before and after tests and replacing the water pump, it functioned normal even with high RPM and load tests.

so, just something to watch out for birp the system with the cap off.. you can feel when the squishing of the hoses removes ALL air from the system . then fill to the high level line, and put the cap back on and you are done.