87 Octane... Or more?

Uh Oh! Get the popcorn ready!

Click on me!


1.) Trust the owners manual

2.) Or this: From The US Federal Trade Commission, Consumer Information:

"It may seem like buying higher octane 'premium' gas is like giving your car a treat, or boosting its performance. But take note: the recommended gasoline for most cars is regular octane. In fact, in 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. Your best bet: listen to your owner's manual. The only time you might need to switch to a higher octane level is if your car engine knocks when you use the recommended fuel. This happens to a small percentage of cars."

There is other good, basic information regarding higher octane fuel on that website.

3.) If you don't trust either of those, then trust the octane engineers/chemists. They would make more money if they pushed Premium Gas/Petrol on everybody, but they don't:

https://www.exxon.com/octane-rating

Hopefully this will quell any Octane Conspiracy Theories and whispers of Government Plots before they gain any traction.

For more info:

I'm certainly no expert on the science of fuels, but this what I know about octane:

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. The higher the number, the less likely it is to ignite under the pressure created during the compression stroke.

But octane isn't an additive. It's a number/a rating, a measure of how resistant a fuel is to ignition under pressure.

The octane index rating is not based on a quantity of a chemical in the fuel mixture, but is a measure of the efficiency of the fuel blend, expressed as a ratio, relative to the efficiency of a pure hydrocarbon, which would have an octane index rating of 100 (or 100 percent). Because gasoline is made up of many different hydrocarbons, the octane rating is a comparison of the anti-knock characteristics of the blend relative to the anti-knock characteristics of a pure hydrocarbon with a 100 percent rating. Aircraft or racing fuels have a rating above 100 because the additives in the fuel raise the efficiency beyond that of a pure hydrocarbon -

Octane is measured by operating an engine under two different conditions and averaged to result in the rating you see displayed on the pump. The first method (R, or Research Octane) is to test the fuel mixture for its anti-knock characteristics (as a percentage of efficiency to pure hydrocarbon) when the test engine is under load, the second test (M, or Motor Octane) measures the anti-knock tendencies when the engine is free-wheeling. The average of the two results is the percentage that is shown on the pump (R+M/2).

Higher octane gas is processed through additional steps that further refine the blend and cause it to burn more slowly than lower octanes. These additional processes are what contribute to the higher pricing, but that does not mean the higher octane will offer any advantage over other blends in many engines. Higher Octane fuels do not offer any better fuel mileage, increase engine horsepower, or make the engine start quicker. Higher octane only reduces the likelihood of engine knock or ping. Anyone who claims otherwise is assigning qualities to it that do not exist and should look to other reasons for the perceived benefits.

potency said:

Thanks for the input! I've since then been following what the manual has called for. Like a lot of you, I've been at a few Grom forums as well, and I was surprised to see some owners/forum posts saying they actually use higher than 87. Which is what prompted me to ask out of curiosity, I'm sorry if I came off as clueless on what fuel to use.

Fang has been an absolute guru on these forums, so I was definitely looking foward to your civilized, prompt, informal and friendly response.

Click to expand...

No worries.

I live at 6,200 feet elevation in Colorado and because of that regular gas is only 85 octane, which is equivalent to 87 octane at sea level and other lower elevations. It runs great in my Grom (with slip-on, Chimera intake and Nology plug wire) all the way up to 11,500 feet, which is as high as I've ridden it and runs fine in Denver at 5,280 feet, which is as low as I've ridden it. I added an EJK fuel controller a few months ago and after playing around with settings I was able to get a little quicker acceleration and an extra 4mph out of it since it's not running as lean as it used to.

Higher octane gas might be necessary in places like Phoenix and Las Vegas in Summer months to avoid pre-ignition and also might/probably will be necessary in a high compression engine, as MNNTHBX mentioned. For instance in a Yamaha R1 with 13:1 compression, but the Z125 is only 9.8:1 (the Grom is 9.3:1).

If you install a BBK to either bike, then a higher octane gas becomes necessary, both because the compression is significantly increased and the temperature in the cylinder and head goes up dramatically as well. The larger the BBK in cc's is the more important higher octane gas is, along with possibly a high volume oil pump and an oil cooler. A colder spark plug can also be beneficial in some cases, such as in high air temperatues and high load conditions on the engine (WOT for extended periods, which is how a lot of Grom owners run their bikes) or sustained high speeds, because these conditions all act to increase engine temperatures.