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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
70 duster full chassis super pro 416 CNC Indybrock heads 727 w/brake
best so far 1.212 60 6.219 in 1/8 at 110.88 9.768 at 137.81 1/4
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