If you want a better running car and increased mileage try sea
Foam. It pretty much cleans all the carbon out of your valve train. I sea foamed my c6 every 2k miles and it would smoke like a freight train until it was all burnt out. Stuff works amazing and keeps your engine clean. Clean engine=happy engine= improved mileage/ last longer. Regardless what octane pump gas 87-93 your going to get massive carbon build up. Take my advice. Sea foam your car and it'll be the best 10$ you spent on it! Just apply 1/5 in crankcase, 1/3 in brake booster line, rest in your fuel tank. It'll do it all