Cheers guys, still none the wiser! Oem sounds good, but what about Cosworth or HKS stopper type? Improvement or not.......
I know this is an old post, but....
Some things to think about that no one seems to be bringing up at all.
The reason for different thickness head gaskets has to do with whether or not a head or block has been decked (milled or shaved).
The idea is to keep the head the same distance from the top of the block.
There are two reasons for this, CR and quench area. The 4b11 is a quench head.
Therefore the piston is in close proximity to the head at TDC.
So there are two issues to address. During compression, if the quench area is increased, detonation is more likely due to reduced turbulence in the combustion chamber. During the exhaust cycle, if quench height has been reduced, then the piston has the possibility of striking the head at high rpms due to rod stretch.
The consensus seems to be that Absolute minimum height is .036 or .9mm with steel rods. Otherwise contact can occur. The maximum varies between .040 and .050 depending on who you talk to. Obviously better fuels can run a larger quench due to better detonation suppression. But after .050 you lose the benefits of a quench head altogether.
So stock quench height is .040or 1.0 mm.
The other factor is rpm. If you are staying at stock. You could push the quench down to .9mm for better pump gas performance. As you increase rpm, rod stretch increases as well. So the minimum quench height grows to avoid contact.
So when choosing a head gasket you need to consider mostly the bore diameter and your overall assembled piston to head clearance. CR should not be a deciding factor in head gasket selection, that is determined by piston, rod and crank and chamber shape.