ah, I had them on a 302 and I was pleased. I've got another set now and I will be polishing up the ports like the last set when I get a little spare time. I belive there is a small emmissions bump in the exhaust port if I remember correctly. If you don't port them, at least grind that down a little. I saw that huge post on here about headers and p-heads on a 37 Ford.......I showed it to a friend yesterday who has a 351 in a '37 and he thought it was so cool he ended up joining us here as Blue37. Later.....