I have used both the RC12YC and RC9YC on my edddy RPM aluminum headed 518 wedge with 10.29 to 1 comp and my 464 Eddy headed 10.46 to 1 comp. ratio little motor Both work well on the street and at the track with those plugs, BTW I am at 3000 FT above sea level also
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Both work well on the street and at the track with those plugs, BTW I am at 3000 FT above sea level also 
