Premium, in fact, sometimes is worse fuel than regular. It resists knock because it's harder to ignite than lower-octane fuels. As a result, some engines won't start as quickly or run as smoothly on premium, notes Gibbs, the SAE fuel expert.
High-test does have a potential fuel economy benefit. It is slightly denser than lower-octane gas, meaning there's a little more energy in a gallon. But the small difference is hard to measure in real-world use, and that same density can contribute to undesirable buildup of waste products inside the engine.
No data show that engines designed strictly for regular run better or longer on premium.
The Federal Trade Commission, in a consumer notice, emphasizes: "(I)n most cases, using a higher-octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner."
There is "no way of taking advantage of premium in a regular-grade car," says Furey.
"There is no gain. You're wasting money," insists Jim Blenkarn, in charge of powertrains at Nissan in the USA.
"No customer should ever be deluded into thinking there's any value in buying a higher grade of octane than we specify," says Toyota's Paul Williamsen, technical expert and trainer.
Usually this is done on cars that run premium fuel in case it can't be found, or if the fuel is bad to prevent damage. Since an eco car wasn't designed for premium, I seriously doubt Honda would have advanced the nominal timing beyond the timing associated with the fuel that the engine was designed for.
