this was posted to me in tech thread by smokeless ef

"I have always been told that the extra metal in the y8 head, makes up the quench area.

Its supposed to squirt the a/f mixture to the middle of the combustion chamber for more efficiency.

Its said that it also helps to suppress predetination by keeping the a/f mix away from the sides of the chamber where hotspots might develope. i believe its called a pentroof style chamber. the b18c5 head has a similar chamber. the intake runners on the y8 head are not straight. the port splitter is angled to create a swirl in the chamber for better efficiency.


Also, you can boost the Y8 no problem, but if you do pick up a Y8 I'd re-shim the oil pump or buy a high flow, because those oil pumps are really restrictive and don't give the proper lubrication under high RPM's.

You can use the Y8 head on a Z6 but the head stud issue, the upper left stud on a z6 is raised where as the y8 studs are all the same height. Meaning you would need to use 9 y8 studs, and 1 z6 stud or it will strip the threads in the block when you drive the car."