The 6X's I have are 6X 4's. They are 92 cc's. Large valves with screw in studs. On a 455 they could give you around 9.6-10 to one compression depending on the pistons you are using. They really are the best thing going for a 455 for street use. These babies barely have carbon build up since the rebuild. Nice heads that were the originals on my 79 TA. They were only available on the highest performance 79 TA's. Great heads for only $350.
