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Max Sluiter
 
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Join Date: Mar 2006
Location: So Cal
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Quote:
Originally Posted by spuggy View Post
The 930 heads use a (trade-marked) alloy under license from Rolls Royce known as RR350 - this symbol is cast on the 930 head. RR350 is also known as AMS225B, and used for bearing support housings in more than one gas turbine motor. Which sounds like a fairly hostile environment.

Bill V says in one thread that he suspects the standard alloy in N/A heads (pre-993) is AMS4220. AMS225B (RR350) is rated for use up to 600F and AMS4220 is rated up to 400F.

Might just be over-engineering by the factory (like the 10 pound recirculation valve assembly). Many folks - including the big HP guys - seem to be running SC or 3.2 heads without issues.

That said, the factory apparently used RR350 for 993 heads (together with ceramic exhaust ports).



Isn't heat transfer from the exhaust valve primarily through the guide? I thought a turbo failure mode was the guides wear beyond spec, the exhaust valve stem locally overheats and the valve head drops off into the combustion chamber. Ouch.

The 935 had an oil channel drilled into the exhaust valve guide which I believe was intended to address precisely this problem - but apparently it's only really essential for the Mulsanne Straight..
Good summary of useful information.
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1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

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Old 08-28-2010, 04:43 PM
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