If I were to swap aussie 2v heads onto 4v closed chamber engine running 10.5 compression what would the resulting compression change be? If its high about 11 or 11.5 what head gasket could I run to lower the compression if possible.
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Auzzie heads are closed chamber! so the comp. ratio should be close to the same. The only difference is, ofcourse, the smaller ports. A head gasket of .043" may be a little thicker than stock (.035"??). I have also read of some machinists using 2 head gaskets. To lower the compression ratio, you can also: use a cam with more duration and/or valve overlap. Also you could Polish out the combustion chambers (increase capacity), or increase the rocker arm ratio (increases duration), although a ratio larger than 1.73:1 would be hard to find, and the stock ratio streeses the valve train enough already. Regards, Marlin.
Dan Jones, fellow P-car owner and having extensive knowledge of the 351-C and its various heads and intakes, has told me that 11 to 1 CR is very liveable with the Aussie heads (which I have in addition to the 4V closed chambers, though I have not yet run on the Aussies). His point is generally that the closed chambers produce a better squish/mixing of the intake mixture, reducing the likelihood of hot spots that would produce detonation. I think he has an article on Daryl's Stang Stable website under the 351C resources that may elaborate. He gave me the thumbs up on my build, having a Weiand Xcelerator intake, KB flat top hypereutectics with otherwise basically stock bottom end, and a moderate cam.