Originally Posted by
B16CVH
Its right what you say about the pistons having a clearence to the head face but the thickness of the gasket does alter the compression ratio, the thicker gasket will create a larger squish area lowering the compression while the thinner gasket will reduce the squish area and increase the compression ratio. It wont make a huge difference but it does...FACT!
Thats why you can buy various thickness` of gaskets which makes up the "extra material" from having your head skimmed.
Very true. One thing must be kept in mind though. Usually CR is only reduced to counter detonation. One of the reasons for the proper squish clearance is to aid gas mixing and prevent detonation. Using a slightly thicker than normal head gasket can actually make an engine more likely to detonate because the squish is not working well anymore, but the CR is lowered too little to compensate. Using a spacer plate or similar to considerably reduce the CR is another thing.
Back to the point: The whole engine should be specced as a whole, including the gasket thickness. Extra care should be taken when mixing pre/post -95 or euro/us zetec parts.