|
Hello John,
Personally, I think your estimates do not reflect what actually happens in a running engine. My guess is the actual environment is much more complex than a few numbers on a spreadsheet. The heat and the mass of the parts varys widely. As I said before, my actual measurements and the published valve expansion figures would need to be incorrect by a factor of 10-20 times for the running clearance to be smaller.
I have done some more research and all of my sources agree that the actual clearances in a running aluminum block and head engine are greater, by a significant margin, than the cold stationary gap. I believe this explains the unusually tight exhaust valve spec by Porsche. They knew that the expansion of the aluminum head and other parts would result in a much wider gap under actual running conditions. The figures associated with iron engines have much smaller variances. I trust the judgement of the people who design valvetrain to know from experience which is correct. When you make some actual measurements, I would be interested in the results.
__________________
Paul
|