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I have ran both the AR 3911 and the NGK 7173 both extended tip only change was plug in my case car ran same et but with the AR 3911 I gained 1 mph and the car idles much better this was back to back test same day 30 minutes apart.



Woody... whats the compression on your engine... was
that with the W-5s





no this was with the Indybrocks with the motor at 12.5-1 and that was install brand new NGK's made 1 pass then installed brand new AR 3911.
The test was done because my machinist swears by the Ar's



I'm trying to figure out what plug to run in my W-5s
for my drag week car, 11:1 ... I've been using Champion
race plugs for my W-9 but they are pretty pricey