Here's my three cents worth, I have tried Bosch and Splitfire plugs in other Japanese engines and found no improvement in fuel mileage or performance. The OEM has engineered the engine (combustion dynamics, fuel delivery, and ignition) to provide the best driveability, reliability, and performance for any specific stock engine. If you are only trying to maintain what is already provided, then stay with the OEM recommendation. If you are re-designing the engine to produce higher performance, then you should select an appropriate spark plug based on your own engineering expertise, or at least based on the recommenadtions of an experienced engine tuner. You can't seperate the total package, the ignition system (including the spark plugs) must play well with the fuel/air system and the mechanical aspects of the engine. I don't think that that any spark plug would improve performance or fuel economy in a stock or nearly stock engine. For my money, I would stick with the OEM spark plugs.