Im going to try the 4's since the autolite's and AC'S were very similar.My plugs just were way to clean even after putting decent miles on them.I didn't pay much attention to gapping them though, other then just comparing by eye sight the gap.Hopefully the NGK UR 4's gapped .35 will be a better plug for my application and maybe I will see the plugs turn that desired tan color after accumulating some mileage.