MY IROC IS TIMED AT 8 DEGREES ADVANCED.THE THING RATTLES LIKE HELL UNDER LOAD.I REPLACED THE KNOCK SENSOR BUT DID NOT USE TORQUE WRENCH TO TIGHTEN IT. ALSO THE SENSOR PLUG IS NOT AS NICE AS IT SHOULB BE AND IS A LITTLE JACKED UP.ARE THESE THE CULPRITS AND DOES ANY ONE HAVE ANY RECCOMENDATIONS? RAN AT 6 DEGGREES ALREADY AND DID NOT RESPOND THE WAY A 383 TPI SHOULD. HEADERS,STOCK PLENUM,K AND N,STOCK RADIATOR. PROGRAMMED ECM FOR 383.......THANKS GUYS/GIRLS.

1st change the plug end.
What grade of fuel are you useing?

USING CHEVRON 91 OR 76'S 91.ONLY PREMIUM. HAVE NOT CHANGED THE PLUGS IN 3 MONTHS. ONLY HAS 300 MILES ON ENGINE.
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OH IM SORRY YOU MEANT THE PIGTAIL, ILL DO THAT AFTER WORK TODAY!