Hey guys, im going to be buying a new head gasket, and i see all of these different measurements. as in 76 mm 77mm 78mm 79mm and 80mm. Are these actually measure .077mm and so on of thickness or is that a bore measurement?

 

its bore

 

its the cylinder bore and the stock bore for the z6 is 75mm. best gasket to get is OEM.

 

I would do that, but when i bought my car someone had built the bottom end and i am not sure how large over they bored it. I guess i could have to get a micrometer to measure. Is it ok to use a smaller bore head gasket than the cylinder bore?

 

You want the gasket to be larger than the bore by at least .5mm (.020"). OEM gasket thickness should be in the ballpark of .030" (.75mm)