These are replacement single plug cylinder heads of S&S® 3-7/16" and 3-1/2" bore P-Series engines, and for 1966-'84 HD® shovelhead engines that have been upgraded with the S&S® Retro Conversion Kit. Cylinder head kit includes front and rear cylinder heads, complete with valves and springs, cylinder head gaskets, pan cover gaskets, and exhaust port gaskets.
These are not service part cylinder heads for panhead engines. They will not fit on stock panhead cylinders.
Compression depends on piston type and engine displacement.