Superjet westcoast head help!!!!!!

The domes should have a number on them, near where the plug mounts. You may need to remove them to see the number. Number would be the size of the domes in CC's. Some of the early heads/domes did not have numbers, and in that case the only real way to tell is by CCing them.
 
i just bought one of these and you have 30cc domes but you have to use a stock head gasket which adds about 5 to 6 cc so really your at like 36cc and should be between 170 and 180 psi. you are fine to just bolt on and run on pump gas 91 plus
 
I was using the ADA Chart, with 30cc domes. Pineapple is right, if you are using a stock gasket that is going to add CC'a and a lot of volume. That would lower compression considerably. I am more familiar with the Westcoast Kawi head which uses a special very thin gasket. I am unsure on the Yamaha if you use a special thin gasket, or thick OE type.
 
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