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Valve seat angles 120-130

posted by  jparker3 on  Sun Aug 3 19:03 CST 2008
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last visit: Tue Jun 9 18:47 CST 2009
[RELATED]

Paul,

I never said that was a quote from you, but its something that is heard all of the time. Do you spend any time on the turbobricks performance forum?

As to the seat angles. After pulling out several factory manuals, I can find no reference to anything other than a single 45 deg. seat angle, which is consistent with what I see in all of the heads I dismantle. The only reference to 20 deg and 70 deg is in the rebuild sections, where it is advised that if the 45 deg seat is too wide after grinding, it can be reduced by 20 and 70 deg. stone cuts.
Yes, there is a machined area below the seats that is sometimes as much as 1/2" long leading into the port bowl, and often ending in a ridge. I don't consider that a seat angle although it could be a matter of semantics.

All that said, the only important point is that the heads on any of these engines essentially only have one wide ( too wide ) 45 deg seat, with the same ( 44.5 actually ) on the valve, and that head flow, and thus performance, can usually be improved by adding additional seat and valve cuts.

John
V-performance.com





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