Originally Posted by Fast355
Having run his exact engine, the OEM plug is TOO HOT for that application....The dynamic compression ratio of a stock L31 is too high to be able to run enough timing to maximize the power potential of the vortec cylinder heads. The hotter heat range is likely contributing to his detonation issue. Not to mention the TBI ignition system is setup to fire copper plugs, not iridium or platinum both of which typically require more voltage to jump the wider gap. A properly gapped (.035") set of R42LTS plugs would work well for him.