What would be better to do?

Mix 110 octane with 91 premium to a 50/50 ratio

or just run 110 octane

Why do you want a high octane fuel to begin with? Almost all bike are fine on pump premium.

William1, on 07 July 2012 - 09:24 AM, said:

My bike runs fine on just regular premium, but I hear that the higher octane makes the engine run colder and I was wondering if mixing it would still make it colder because buying gas at around $8 dollars a gal is a lot of money. I would also just be running the 110 for races and not for just riding around my land.

If your motor does not detonate under load, adding higher octane will not raise the peak power numbers at all. In fact, they will probably drop. It WILL make your bike run 'crisper' if your jetting is off, or if you use cheap (old) gas.

Unless you increase the stock compression, you don't need HO gas.

Do not spend the money, All that will happen is your bike will make less power. Practice riding and save your money for tires, chains and tear offs.

KTM_Pro, on 07 July 2012 - 10:04 AM, said:

Yes it will make your motor run cooler. Cooler not cold! I splash race gas when I know I will either be in an area with poor gas quality or very hot temps.

It's not going to lower the temp of your motor, unless your motor is running too hot due to detonation. If there is no detonation, there is no need to slow down the fuel burn, which is what higher octane fuel does.

i dont think its adviced to run high octane unless its a tuned motor mate

Krannie, on 20 July 2012 - 11:51 AM, said:

My experience with a infrared thermometer that it indeeds lower a heat soaked motor's temps.

weantright, on 20 July 2012 - 12:05 PM, said:

Really? By what, 10 degrees?

25*F on a EFI 2t snowmobile via a water sensor. 17*F on a 4t bike. Did this to stop it from overheating before we replaced the rad cap. Is it a lot?? No but just like a rich jetting, motor will run cooler and have less power. Most stock bikes run good up to 94-96 octane. After that power loss and jetting changes are needed. Plus side is the added lead to the top end.

KTM_Pro, on 07 July 2012 - 10:04 AM, said:

You heard wrong, from someone that doesn't have a clue what they're talking about.

Combustion temps are determined by the fuel/air ratio (jetting), not by the fuel you run.

High octane fuel DOES NOT burn cooler.

High octane fuel DOES NOT produce less power.

High octane fuel DOES NOT produce more power.

High octane fuel DOES NOT burn slower.

Gee Chokey, so NEGATIVE

Yes, high octane costs more

Yes, High octane sounds cooler

Yes, high octane will intimidate the naive

William1, on 21 July 2012 - 07:47 AM, said:

Nope. I just happen to know a tad bit about fuel chemistry and combustion dynamics.

Every time one of these threads pops up, the same old myths get tossed out as "fact". It's amazing how pervasive those myths are.

It's also amazing how completely misunderstood the role of "octane rating" plays in fuel. People attribute all sorts of amazing properties to it, when the truth is that the octane rating of a fuel is nothing more than a measurement of a fuel's ability to resist thermally-induced molecular degradation. It's that degradation that lowers a fuel's auto-ignition point enough for it to spontaneously ignite without an external ignition source. That's it, nothing more. Octane rating has absolutely nothing to do with combustion temperatures, flame propagation speeds, potential energy released, or any of the other myths that people try to pin on it.

Edited by Chokey, 21 July 2012 - 12:16 PM.

What you stated is correct and the out come is slow burning fuel.  Look deeper into what you just typed  and you will find the same thing I stated but in different words. What octane has more BTU's, 87 or 110? Smart words don't mean your smart!

Edited by weantright, 21 July 2012 - 01:59 PM.

weantright, on 21 July 2012 - 01:41 PM, said:

Octane has absolutely nothing to do with burn rate, or BTU content. You're wrong, and the sad thing is you don't even want to learn correct information.

Here's a quote from Jim Wurth from Sunoco Race Fuels when discussing the myth of octane rating being related to flame propagation speed.. He explains, "That's simply not true. A perfect example is Sunoco Maximal, which is our fastest burning fuel, and coincidentally one of Sunoco's highest octane Fuels at 116 (R+M) / 2. A lot of Pro Stock teams rely on Maximal for those sub-seven second runs. When they are turning 9,000 rpm or more, the fuel has to burn pretty quickly to achieve complete combustion".

The energy content of pump gasoline, regardless of octane rating, is approximately 115,000 BTUs. There are race fuel formulations that have higher BTU content, some as high as 125,000 BTUs, but that is strictly determined by the various chemical components used to formulate the fuel, and is irrespective of the octane rating.

There are plenty of gasoline formulations that have identical octane ratings with wildly different flame propagation rates, and vice versa there are plenty of formulations with very different octane ratings that have nearly identical burn rates. The rate the flame travels across the combustion chamber is dependent on many things (fuel chemistry, mixture turbulence, air/fuel ratio, etc.) but octane is not one of them.

As I already stated, the octane rating of a fuel is nothing more than a measurement that determines that fuel's ability to resist auto-ignition (detonation). That's it. Nothing more.

I realize I'm not likely to convince most of you, because "It's what you've always heard" or "you read it on the internet" or "because so-and-so told me", and that's fine, believe what you wish. That doesn't mean I can't at least post correct facts about the subject, and maybe somebody will learn something, even if it isn't you.

And no, "smart words don't make me smart". But four years of college for engineering, and 40+ years of wrenching, riding, racing, building engines, experimenting and breaking things, dyno testing, and helping with dad's race cars, does mean I know a little bit about it...

Edited by Chokey, 21 July 2012 - 02:44 PM.

There's a HUGE amount of data here on burn rates:

http://www.gonefcon..../combustion.htm

Note that the article stresses multiple times that octane rating has nothing to do with burn rates.

Chokey, on 21 July 2012 - 12:07 PM, said:

Ya missed the sarcasm and humor. Lighten up! Notice I made all mine 'Yes'. Geez!

Another engineer here, fuel systems. I have to say, I'm on Chokey's side on this one for sure. LOTS of myths and misinformation out there, sadly often spread by people with strong reputations. Often performance differences between low and high octane fuels are credited to it being octane level, when in fact its the fuel blend, end points, etc, specific to those two specific fuels, not necessarially the octane rating.

Then we can get into whether you are talking motor octane, research octane, (R+M)/2, leaded/unleaded, oxygenated/non-oxy, specific gravity affect on jetting, reid vapor pressure, etc etc. There's a lot more to fuel than just octane rating.