tony barnhill said:
hehehehe......."X" heads = European castings....not offered in North America.
I'll let you go from there.
NAH, this has been fun.....but, here ya go:
They were European offerings...back when there was a rash of cracked heads, lots of dealers had these sent over from salvage yards in the UK, rebuilt them & put them in customer cars. Here's the difference between them & NA heads:
1. The combustion chamber is smaller so it increases the compression ratio.
2. The intake valves are larger than any valves offered in NA heads.
3. The head flows gas smoother.
4. The area around the exhaust guides is larger than the area in normal heads so the exhaust also flows more smoothly.
When customers got their cars back (usually heads replaced under warranty) they were excited about the increased power. Remember, these are non-emission heads.
......& if you can't find an "X" head, look for an "O" head!
hehehe