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Premium fuel vs regular

M

Mad Steez

New member
I'm getting conflicting info regarding whether or not there is a benefit of using premium fuel in my engine (2004 Honda 225). My assumption is that premium fuel would burn more efficiently and delay the breakdown of ethenal. The owner's manual just said to use 86 octane or greater. But I've also heard premium could possibly damage the engine. I can't figure out why that would be the case, but it still made me question if using premium is a good idea. Thoughts?
 
Standard 87 octane works fine. The manual states 86 octane or higher. Try to get non-ethanol as much as possible. If you are not running through a tank of fuel every two or three weeks, then be sure to add a stabilizer, like Stabil (marine) or Startron. If you are doing a lot of low speed motoring - trolling or just futzing around - also add a decarbonizer like Sea Foam or Yamalub Ring Free. Some marinas in my area only carry 89 octane, and one carries 93 octane. In some cases I have had to use those, but notice no difference in performance or efficiency. Whenever possible, I fill up with fuel that has been treated with Valvtec, which is both a stabilizer and decarbonizer. In my area, it is about 10 cents a gallon higher, but is actually cheaper than adding a separate stabilizer and decarbonizer.

The reason some four stroke high-compression engines require a higher octane is to prevent pre-detonation, or knock. Contrary to popular opinion, higher octane fuel actually detonates slower. The knock sensor in your 225 will detect any pre-ignition and will adjust the spark accordingly.
 
I would have to second pretty much everything that chawk_man said. But, for more in depth clarification of his statements, here are a couple of facts:

A gallon of "regular" or 87 octane fuel contains approximately 111,400 BTU of inherent energy. Care to guess what a gallon of "premium" or 92 octane contains in the form of energy? No need, I'll tell you. The answer is; approximately 111,400 BTU!

So, it is clear that there is ABSOLUTELY NO power advantage to using a higher octane fuel. You can't squeeze any additional power out of a gallon of premium than you can a gallon of regular.

The ratings, or numbers, associated with "quality" for regular and premium gasoline are pretty much universally derived from the amounts of particular types of hydrocarbons that are used to formulate each fuel. Basically, the two hydrocarbons used to obtain the "ratings" are isooctane (C8H418) and n-nepthane (C7H16)

Simply put, (because that's all I understand anyway) n-nepthane is a hydrocarbon that is somewhat volatile and ignites readily without much "persuasion". Isooctane, on the other hand, has a tendency to be a little more difficult to ignite and, once it does, will burn slower and "smoother" in a very contained and predictable manner.

Staying with simple here...87 octane gas will contain a mix of 87% isooctane and 13% n-heptane. While, on the other hand, 92 octane, "premium" gasoline would be comprised of 92% isooctane and 8% n-heptane.

And, like chawk explained, this is all done to address the issue of detonation that can take place in higher compression engines. The "smooth predictability" of the isooctane is important for a flame that has a tendency to advance consistently throughout the combustion sequence rather than sort of "exploding" and causing the kinds of undue pressures within the cylinder associated with "pinging" and detonation. A sure engine eater if allowed to happen for extended periods.

The bottom line is that it is a waste of money to run a higher octane fuel in an engine that does not REQUIRE it. There is just no useful data to suggest that there is ANY advantage to using a higher octane rated fuel but there are some people in the industry of engine performance that would tell you that there may actually be some DETRIMENT to unnecessarily using a higher octane fuel than you need.

Cheers, and thanks for bringing the subject up.
 
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