[4dblnkldude]

Hello, I have a 455 in my 69 firebird. Street ported edelbrocks, headers, flowmasters, torker 2. MSD ignition, and a holley 850 that was prepped buy a pretty well known local guy. My problem is I keep going through plugs, its always been this way through a few different iterations of the engine over the years. I clean the plugs at 150 miles or so. And I change them at maybe 300 miles. The car does not seem to run any different until about that 150-200 mile mark. The strap is clean but the rest of the plug has black carbon all over it. I have tried numerous carb and timing adjustments and nothing seems to work. Now granted the car does get backed out of the garage often, Idle for 5 minutes to warm up. then back in later. Any other ideas I may be missing? It has been 7-8 years now, so 16 or so sets of plugs. I run NGK R5671A-8 plugs. What really baffled me was last year when I put the roller cam in, I took the heads off for new springs... the piston tops were barely charred with no carbon at all on the top of them. A quick wipe with a rag and the slugs were almost brand new again. Do I need a hotter plug...colder plug? TIA!