I had a problem with the '65 Chev C-10 daily driver I had with a 355 SBC the Accel shorty plugs crapped out about every 3 months,I found that the AC Rapidfires gave me enough clearance at the headers.The surprise was it seemed to smooth out the camshaft lope and ran noticebly stronger and mileage picked up and they were still going strong till I sold it two years later.I put them in 4 other cars and had the same results,two of those were Fords,Rapidfires I give a thumbs up!