High Octane Fuel or Regular?

[FrankyArseneau]

Is is better for the engine to put high octane fuel(Supreme) of just regular fuel in a sportbike?

[VermilionX]

once you get your owner's manual, these kind of questions will be answered.

anyway... mine says to use only a minimum 90 octane.

here in CA, we have 87, 89, 91... so im usng the best being 91 premium unleaded gasoline.

[DragonSlayer]

i only use premium, which is atleast 91 i use to see it being 93 at someplaces but not anymore, just 91 now

[jmillheiser]

Only 91 octane graces the tank of my bike.

My cage gets mid-grade.

[Ninja Geoff]

It depends on the compression ratio of your engine. Bikes like VermillionX's have a high compression ratio. And after compression, comes combustion. BUT compression makes heat so with enough compression fuel and air, you don't need the spark plug to fire to get the air/fuel mix to go boom (basic principle behind deisle). Now, the higher octane stuff has a higher resistence to combustion, so that's what's needed so you're not getting man's worst enemy, premature firing. Now, with say a car with a modest 8.5:1 compression ratio, you only need 87, and adding 93 won't do jack "poo poo" for your car. BUT if your car NEEDS 91+ and you've been puting 89 in it, once you start using 91 you'll notice a difference, mainly bcause it's not misfiring any more. Compression ratio isn't the ONLY factor involved, but it's the main one. The best fuel to use is the one recomended in your manual. I know my dirtbike sure as hell perked up when i used 93 instead of the 87 it was getting.

[FrankyArseneau]

Ok
Thats sound a little complicated at firt but i am getting the point here.
Thanks for the help everyone.

[CNF2002]

Put in what it says to in the manual. Cant go wrong there!

[scan]

Basically - high octane gas is to stop pre-ignition. Pre-ignition is when the engine is hot enough to ignite the gas without the spark plug firing, causing a pinging sound when the engine is running (or most likely when under acceleration). Find out what the owner's manual says. Also some have reported that their bike do not suffer from pre-ignition with lower octane gas. Experiment at your own risk.

[jmillheiser]

Most bikes have high enough compression ratios to need 91 octane.

Even my lowly CX500 has a 9.5:1 compression ratio which on an old carbed bike is 91 octane territory. Air cooled bikes tend to have higher octane requirements than watercooled bikes as air cooled engines dont have as stable an operating temperature as watercooled bikes.

Most UJM style bikes require 91 octane due to their air cooled engines. V-Twin cruisers may or may not need permium, usually the less powerful ones can get away with regular unleaded.

Dual sports and dirt bikes usually only need 87, where sportbikes pretty much all call for 91.

Fuel injected bikes can usually take lower grade gas, but you will get better fuel economy with better gas. The fuel injected bike prevents detonation from low grade gas by simply retarding the timing and richening up the Air/Fuel Ratio which will prevent detonation.

[flynrider]

What Scan describes is actually called detonation. When the fuel/mixture explodes prematurely due to temperature and pressure. This causes extreme stress on the piston, rods and crank, since they're trying to move the piston up, while the exploding fuel is pushing it down. If left unchecked, the usual result is either a bent rod, or a hole blown through the top of the piston.

A gasoline's octane rating is a number that describes the fuel's resistance to detonation. Higher octane fuel is less volatile, and will not prematurely explode in engines that have high cylinder pressures and temperatures (i.e. high compression ratios). Engines are designed with a particular grade of gasoline in mind. The designers will evaluate the typical temperatures and pressures in the combustion chamber and recommend a particular grade of fuel. Using a higher grade has no benefit, and can actually leave some carbon deposits behind, if the lower compression engine doesn't completely burn the less volatile fuel. Eventually, carbon deposits can cause pre-ignition, which is similar to detonation in that red hot carbon specks can cause the fuel/air mixture to ignite prematurely.

The above is true for most motorcycles that do not have ignition computers that are tied into knock sensors in the engine (unlike many modern cars). Cars equipped with knock sensors, can automatically sense detonation and mentally challenged the ignition timing to avoid damage.

In a nutshell, you should use the grade recommended by the manufacturer. If you get knocking or pinging, it would indicate a timing or temperature problem, but you can solve it temporarily by moving up a grade. In the extreme heat of our desert summers, I usually have to move up a grade in my bike and car to compensate for the extra hot air coming through the intake.