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Speedy Squirrel Speedy Squirrel is offline
Rocket Scientist
Join Date: Jun 2008
Location: Detroit
Posts: 898
Hmm... I think something else might be wrong with your RTD JP , as the cooling air temp is also quite a bit higher than 130F under load. One has to make sure that the RTD used is compatible with the calibration in the ECU. I wonder if yours is.

It is not odd to find the maximum surface temperature atributed to a "factory source". The vaults are quite full with the secrets to the 200 mpg carburetor; we have no more room secrets ;-).

The reason is that the maximum surface temperature allowable is well below the autoignition temperature (around 530 F) due to the effect of the combustion process itself. The flame front starts at the plug and as it advances the pressure and temperature of the mixture in front of the advancing flame front increases. If the walls are hot enough, it will ignite and produce knock. Obviously this tendency is highly dependent on the combustion geometry, so an easy number for all engines does not exist.

Air-cooled engines have a problem here, since the hot spot is the exhaust valve, and it is a big one that is hard to cool; the fins are a long ways away. Check out a cross-section view of the Porsche cylinder head some time, and you will get an understanding of the problem.
Old 08-03-2009, 03:04 PM
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