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cnavarro cnavarro is offline
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Join Date: Oct 2001
Location: Momence, IL 60954
Posts: 1,854
I couldn't find the best way to explain this, so I got this off google:

"The purpose of the oil squirters is to cool the aluminum pistons. There are two reasons for this. First of all, the strength of aluminum decreases rather quickly as the temperature is elevated. With the emphasis on decreasing the mass of pistons (a reciprocating part) the amount of material is reduced to the absolute minimum, so the margin on strength is not large. Any further decrease in strength due to heating should be avoided to maintain the mechanical integrity of the piston. There is also evidence that cooling the pistons can reduce the likelihood of pre-ignition (and possibly detonation). This can be caused by hot spots (on sharp edges of the piston-top) lighting-off the mixture before the spark plug fires. Rounding off any sharp edges on the machined piston-top can also help prevent this." for the entire article on oil squirters.

This kind of touches back on the discussion of mahle vs. je pistons and the p/c clearances between both brands of pistons. Since the mahle has a higher silicon content and lower coefficient of expansion, it can be run with tighter clearances. The compromise that has to be made for this reduction in expansion is a loss of strength at higher temperatures. The 2618 forging from JE has a lower content of silicon and higher rate of expansion (so higher p/c clearances), but is stronger at higher temperatures and less prone to loss of integrity under these conditions. Just an observation that explains why the oil squirters are so very important and worth the effort.

Charles Navarro
LN Engineering
Aircooled Precision Performance
Old 11-03-2004, 05:01 PM
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