Damn, this is a bit confusing. So what is the difference between the "X" and "U" (or "O" & "Z" as stated in one of the above posts) heads? Does one flow better than the other? Different springs? :BangHead:
Unless they are TA heads nothing. The X heads all had 2.02 valves. "Some" J heads had 2.02 valves. I am not sure if any of the other letter heads did. But, unless they are TA heads, the only difference is either the 1.88 or 2.02 intake valve size. All the ports and chambers are pretty much the same. Even in stock form, the TA heads are the same except the 2.02 valves and the offset pushrods for porting the intake ports out. I believe even the ports in the TA heads are all the same as the rest in stock form.
