I realize asking for 'what plug' can lead to a lot of thoughts, so here is question1970 Swinger 340 4spd. I was told I had 10.5 compression, I use mostly,,,,, straight aviation fuel I get from the local airstrip. I tend to favor Champions, does it really matter, which one of these 3 ? RN7yc, RN9yc or R12YC , use with Taylor StreeThunder plug wires
