He probably uses Q16 due to the fact that it is oxygenated and will generate 4-5% more hp than non oxygenated C12 and C16 fuels. It's legal race fuel and in F.A.S.T. and pure stock, you get your power where you can!! In Jimmy's big block and if it's true, Q16 will take him over 610hp with a jetting change and no more!!
