What's a good spark plug to use for a 96 LT1 with a Vortech supercharger (6-7 PSI boost) and 42 pound Motorsport injectors? Other than headers and better exhaust the rest of the car is stock. I just put in NGK TR55IX's (part 7164), gapped them at .044 and the car runs great cold but when it warms up and I get on it the car spark-knocks like crazy and occasionally backfires. The NGK's out of the box and the stock Delco plugs I took out were at around .060 gap. The car ran great with the Delcos, I just changed them over to the NGK's per the tuners advice. (I got a mail order tune on it for the 42 pound Ford injectors and to raise the rev limiter to 6500). Any help would be apprecitated! I see plug gaps ranging from .032 all the way up to .060 on these cars.

Dave

 

most ls1 fi cars run tr6 plugs, they are one step colder than stock and gaped at .035

 

You need a plug that is 1 step cooler than stock. Your gap is way too big also. You need to be in the .030 to .035 range. TR6's @ .035 is a good combo.