TTI are fine but, the day you get them mock them up on a head and make sure you can get a spark plug socket on all your plugs. Also make sure you have 3/8 inch minimum clearance between your spark plug boot and the header, 1/2 inch to spark plug it self. DO NOT WAIT PASSED THER 90 DAY period. I have bought many sets of TTIs, and have got more than one set that I had to beat up. My own fault, I waited too long. P.S. there isn't a spark plug boot made that can touch a header and not burn.