I have a 540 street motor with 9.5-1 with the dart 320 heads. I'm running the NGK 4091 (R5671A-7) plugs. What gap would be best or is there a better plug. Running a 1050cfm pro system carb.
That is the hottest race plug NGK has. 7 hottest, 11 coldest. If you have clearance, run a projected nose plug. You can try a N9YC Champion or equivalent if you need hotter. Try .035 on the gap, more is harder on cap, rotor, wires and not necessary. More chance to arc. You have to read your plugs to see what the engine needs.