KartDen

Peak power in a gasoline spark-ignition engine sits rich of stoichiometric, not lean of it. Excess fuel both consumes the available oxygen and cools the incoming charge through vaporization, so from a rich, safe baseline, leaning the mixture does increase torque until you pass that best-power region. Past that point, further leaning mainly raises combustion temperature and knock sensitivity, which is the usual explanation for pale insulators and short piston life. The street heuristic of a coffee-brown insulator is therefore a reliability target, not a power target. The open question is whether serious race programs hold the mixture on the hot side of best power because the engine is already treated as a short-life consumable, or whether a white insulator is simply what a frequently rebuilt motor looks like when it is already near that peak. How far do people actually push this, and is plug color even a clean enough signal to decide?