Dear Tom and Ray:

A friend of mine has a 2000 Corvette with the 345-horsepower 5.7-liter engine. Lately, he has been using an octane booster on top of 91-octane premium fuel. He claims that the computer in the Vette can detect the booster and advance the timing to increase horsepower. I say he's full of hooey. It might work, but it's difficult to believe that the booster is making a large enough difference that he can feel it in the seat of his pants. What do you say? -- Keith

TOM: Well, Keith, if he's feeling something in the seat of his pants during hard acceleration, he might need to throttle back on the Metamucil, not the octane booster.

RAY: He might actually be able to feel a bit of a difference, but his description of why he does is incorrect. This car has a knock sensor, which tells the computer when there's pre-ignition, or pinging, in the cylinders. Pinging is caused by premature combustion in the cylinders. And it's usually due to the engine running too hot or the octane of the fuel being too low.

TOM: Pinging is bad for the engine, so when the knock sensor detects pinging, it retards the timing a bit to get rid of it. That reduces engine power by a small amount.

RAY: Now, most civilized humans would never notice this subtle difference, or care. But some knuckle-scrapers whose whole lives revolve around "0-60 times" might notice a difference -- or at least imagine that they do.

TOM: By adding an octane booster, your friend is probably preventing pinging during hard acceleration, and therefore is preventing the knock sensor from kicking in and retarding the timing. That means that the engine is operating at full power, even during the period of greatest demand.

RAY: So tell him that he's half right, Keith, but he should stop driving like a knucklehead. And tell him if I catch him driving like that, I'm going to use my foot and give him something he'll definitely feel in the seat of his pants.