approx every compressed .010 thickness of the headgasket is + or - ( depending thicker or thinner ) 4cc's, so if 1 was .030 and 1 was .040, the side with .030 would have a slight bit higher compression. it's a quick fix, but due to the fact it's still not " right " it won't give yo even burning from side to side, dyno run will show that.