January 27th, 2009

The gas I use for all my vehicles is 87 RON.

If I encounter knocking and pinging, I move up the scale until that stops. But I don't put anything with a higher number in until it is needed.

There's a reason for this: the octane rating doesn't mean "good", "better", "best", despite the clever marketing names that stations give them ("premium", "supreme", etc.) It can be summed up like this:

The higher the octane rating, the later in the cycle the fuel ignites. That's it.

That means if your engine is not knocking and pinging, putting in fuel that has a higher RON (that's the blended octane rating), say 92 or 94 or 108 or whatever, is just a waste of money, and will probably result in a slight reduction in performance. Yes: reduction.

The knocking and pinging from "pre-ignition" can be mitigated with a higher rating so that the spark plug ignites the fuel at the right time in the cycle, and not the heat and pressure igniting it before the piston has reached the top of the cylinder. But just putting in higher octane fuel into your tank when there is no knocking and pinging is only wasting money.

Here, don't take my word for it: http://en.wikipedia.org/wiki/Octane_rating

Remember: It's all about when the gasoline ignites in the cylinder; it has nothing to do with quality.

Read more rants - Top Blogs - Comment on this rant - Email me