Like others have said: Unless you have high comp pistons & cam work, run regular 87 or 89 in it, that's all it needs.

 

The higher octane ratings are for fuels that resist combustion more. High compression engines need more resistance to prevent detonation or predetonation aka pinging. Putting high octane fuel in a low compression engine like the SH will result in the fuel burning slower and later in the compression stroke. That will reduce power and efficiency thus resulting in poor fuel mileage although the power loss may not be significant enough to notice. Because of the low compression engine in the 'Hawk 87 is recommended. But I'm sure the oil companies don't mind you donating a couple extra dollars every time you fill up.

 

A fuel engineer I used to know changed my mind on this subject. When it comes to octane there is no argument - a low compression engine does not need high octane fuel to prevent detonation.

BUT, he advised using the high octane stuff from a known refinery anyway. His reason was that in Australia the higher octane fuels also have a better blend, and whilst the higher octane is not needed you are getting a better fuel. It will burn cleaner, and will contain more energy to give you more power. Octane rating and energy level is not the same thing. Ethanol is a good example of this, as it has a high octane rating but is low in energy compared to a normal fuel.

So fuel quality is the issue, and in Australia the better fuels are the higher octane fuels.

 

this is sounding like a "refined" oil thread...

 

I run pure nitromethane in my bike. It's expensive at $60 per gallon, but well, only the best for my baby.

Your bike is designed to run on regular. Premium isn't better gas, its different gas. But Abdullah thanks you for buying into the misconception.

 

I run 91 octane in mine.
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Regular is fine. I run midgrade at sea level.

 

I run 91 in mine. I honestly don't know if there's a benefit to it. and I don't care. I can afford it, and even if the higher octane doesn't run cleaner, you can bet that the 87 doesn't run the cleanest between the 2. so 91. maybe it helps maybe not.

 

Over advanced timing is the number one cause of detonation on cars with adjustable ignition timing, so if you're bumping it up 4 degrees, you should bump up the octane as well.

I run Chevron mid grade, 89 octane, in my bikes. My 4x4 Toyotas get 87. I put a lot more acceleration load on my bikes.

 

That used to be the case with some brands, but not any more. So yeah, it really doesn't help.

There's no possible way to justify putting premium in a stock Superhawk. The only truthful explanation left is, "I like paying extra for zero benefit."

 

I don't understand why people can't get it! I have been building engines for over 25 years. Carb'ed, fuel injected, aircraft, cars, motorcycle, jets, etc... The simple truth is low compression engines will not burn high octane fuels as efficiently as a low octain fuel! Low compression engines can not compress (thus heat) the fuel enough to properly ignite the fuel, period! No matter what you do to the timing it will still not properly ignite the fuel.

It has always made me laugh when someone puts a race gas in a stock engine and they think that they somehow they gained HP just by adding gas. All they did was loose power and somehow this excites them.

Your (stock) Hawk will run its best on 87 octane fuel, if it pings you may want to have your timing checked.

My hawk is running 12.5:1 compression and just loves 104 VP and 100LL avgas.

 

Is your bike a Diesel? Gasoline engines do not use compression to ignite the air/fuel mixture, they use an ignition spark. Heat of compression is used to complete the vaporization process, thereby burning more of the fuel when it is ignited by the spark.

Tetraethyl Lead was added to gas, back in the early thirties I believe, to prevent detonation in the newer high compression engines (1929 Model A Fords had 4:1 compression and ran fine on 60 to 70 octane).

In my 34 years of teaching Vocational Automotives, I often had students ask if running higher octane improves performance. I always told them NO. Higher octane prevents detonation in higher compression engines. But that doesn't even hold true with some new engines with Direct Injection that can run on Regular at up to 12:1 or more.

The reason I've always run Mid Grade 89 in my bikes is that I like to ride the twisties, and here in California that usually means going up a mountain. I accelerate hard coming out of uphill corners, which puts more load on the engine making it more prone to detonation.

An extra 30 cents per fill-up is worth it to me for the insurance against blowing a hole in a piston.

 

I run 87. I have a theory on this which some may consider. High octane fuel sucks in this bike. If its better, run 110 and try to break 7k rpm or 120mph. You have to tune your bike for the fuel you are running. You could run the 110 octane if tuned properly, but you would be going down just a few jet sizes.

 

OK, maybe i should have elaborated a bit more. You get absolutely no benefit in running a higher octane gas than what the manufacturer suggest unless you are getting a knock or pinging sound, then step up to the next higher octane.

I was just making the statement that for some they think that adding a higher octane increases hp or performance, only a increase of compression will result in added hp (when speaking of the compression chamber and not the rest of the engine)!

No my bike is not a diesel! My thought process was a high compression ratio is desirable for high octane fuel because it allows an engine to extract more mechanical energy from a given mass of air-fuel mixture due to its higher thermal efficiency. High ratios place the available oxygen and fuel molecules into a reduced space along with the adiabatic heat of compression - causing better mixing and evaporation of the fuel droplets. Thus they allow increased power at the moment of ignition and the extraction of more useful work from that power by expanding the hot gas to a greater degree.

 

Thanks surfer. I'm thinking the same way, just don't know if four more degrees of advance would cause trouble on 87. But unless I hear otherwise from several guys who have been running long term on regular with the advance change, I'll go higher octane when I get around to installing the rotor.

 

After reading what I wrote, it never crossed my mind that someone would think i was using compression to ignite the fuel such as a diesel. I just assumed everyone knew there was a spark involved. My bad, sorry!