[JnC]

Higher octane is also hotter to burn. Unless you add forced induction, don't bother running it in car that only needs regular.

Anti-knock sensors retard the timing due to... knock. 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.

I don't see how a knock sensor tuned for regular gas could advance the timing if you put in premium: there's no knock event to measure. From the perspective of the sensor if there's no knock, it would keep the timing mapped for good regular gas as opposed to bad regular gas.

Just my theory... I could be wrong.

 

[JnC]

manual says 87 or higher on the crz. So I went premium. IMO, better is better.

How is it better? The engine wasn't designed to burn it. There's nothing to take advantage of it. You're just making your engine work harder and hotter. Talk to your tech at the dealership.

From a random article I googled... there's more out there. Just search for running premium gas.

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.

 

[JnC]

On the Honda website it says Required Fuel: Regular Unleaded

You can likely get away with running one grade up. Running it sporadically isnt that big of deal as there is some variation from tank to tank. One tank won't do bad things. However, going from 87 to 91 or 93 can be problematic if that's all you burn. I know a fellow at work who had major engine repairs due to just that. I don't recall the exact details, but it eventually messed up his sensors and caused the ecu to make bad choices for combustion. About $2000 in repair costs.

Talk to your tech at the dealership. Seriously. You're talking about spending pennies per gallon to potentially damage your $20k+ car over the long haul.

 

[JnC]

Okay, plenty of cars that run higher octane that are not boosted. To say only boosted cars really utilize it is false. Higher revving motors like preludes,s2000, si's, rsx's require it becuz of the heat that is built up at those rpms.

But those are high compression engines designed for high octane fuel from the outset. And what's the redline on the CRZ... 6500 rpm?

On an engine that is optimized for low octane fuel, unless you do something to the compression, timing, or induction, you're not going to see any advantage by running premium. It's quite possible that Honda set the engine up with some margin to take advantage of tuning as well as better fuel grades in the rest of the world. But without changing how the engine runs, it's not going to take advantage of higher octane fuel. A mass volume manufacturer tunes for the worst case scenario.

Read the article I quoted closely. Look at who is talking. If you don't believe me, talk to your Honda tech.

 

[JnC]

What are these 87 and 91 figures? At UK pumps we have 2 choices of unleaded, 95 RON or 97 RON (premium). Is this different to what you're talking about?

It's a different unit of measure, just like the US gallon is 1.2x UK gallons.

US octane is the average of two octane numbers (RON and MON).

UK octane is as you described, only RON.

Octane rating - Wikipedia, the free encyclopedia

Octane rating does not relate to the energy content of the fuel (see heating value). It is only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where octane is raised by blending in ethanol, energy content per volume is reduced.

Thus a gallon of regular gas has the same energy potential as a gallon of premium. The only difference is the resistance to pre-detonation. And if the premium octane was boosted by adding more ethanol, it has less energy potential than regular. (I say more, as most US fuels contain 10% ethanol.)