Thread: Octane Effects

I currently run 93 octane in all of my saws. I know that this subject has been covered. I tried a fuel called Turbo Blue that is about 107 octane. My saws ran terrible. What causes this? Is the burn rate so slow that it causes the slow throttle responce? Can slightly better performance be had from......say.....89 octane vs. 93 octane?

My dealer recommended that I only run 89 octane and higher in all of our 2-stroke engines. I haven't ever used 93 simply because 89 seems to work great and it's cheaper.

Turbo blue is a crappy race fuel to begin with. Add to that the fact that it is sold from tanks that many times are used to sell kerosene in the winter. Also the volume of sale is so low it is easy for the stuff to go bad in bulk storage.
Ocatne has nothing to do with burn speed. I suspect your saw ran like crap for one of the following reasons. 1 Fuel was bad. 2 Carb was not reset for the fuel. Carb settings for a race fuel will be drasticaly differant the pump gas.

Not that I will ever use them, but doesn't the timing and compression have to be altered to take advantage of the higher octane fuels? Or maybe I have that backwards. Don't higher compression engines require higher octane fuels to prevent preignition? Then, doesn't the ignition have to be advanced to obtain the greatest cylinder pressure at around 15 degrees ATDC? That was always my understanding.

Timing and compression do have to be optimised to get the most out of race fuel. However given the correct race fuel a stock saw will gain quite a bit with only carb mixture adjustment. IMO running premium fuel(ie 91-3) is cheap insurance withe the crappy quality of fuel in most of the country. Padd s 1 and 2 have fuel quality on par with third world countries like uganda!

Originally posted by bwalker

Octane has nothing to do with burn speed.

I always was told that Octane was the rate that gasoline burned!

What does it do?

well im gone tell u. and this aint from an expert. i do believe that higher octane has more usable power, and i dont believe its just more stable. although i do believe it is more stable.
it works good for me in 2cycles.. if it works, thats all that matters to me.
i use reg in my kohler an most other engines . and it works fine in them.
although, if ive got a hard grade to pull,
high octane will make a difference.no doubt about it.as usual jmo

When I was in auto-tech school I was told that the fast burn of low octane was what cause the pinging that was so common in the late 70's and early 80's. The flame front would ( for lack of better explanation ) smack the piston creating the pinging noise. The higher octane would actually push against the piston eliminating the pinging. Maybe I have this all wrong.



Ben Walker could you shed some detailed light on this!

I always run 147 octane with amsoil/stabil/marvel mystery/
promix blend with no trouble. But it still may "ping" unless
I run a Platinum splitfire plug.
I can discuss the physics involved if you all need me to.

Rich,That is pretty much my understanding. Low octane is actually more flammable and more ready to give up its energy. _Which is why it will yield higher gas milage in a vehicle in which it doesn't cause preignition problems. Preignition is the rub-it wrecks everything from milage and performance to the engine itself. High performance engines are generallly designed for high octane fuels because the greater compression prior to ignition yields better power output in a given displacement.

fish ,add a little of grandmaws special cure all to the mix. then take a swig u self.that way whether it works or not
wont make much difference.u still have a good day.

As I understand it, the "octane rating" of gasoline tells you how much the fuel can be compressed before it ignites spontaneously. This spontaneous ignition is called "knocking".
If you use too low an octane rated fuel in an engine that has a high compression rating, the fuel in the cylinder will spontaneously ignites on the compression stroke before the spark from the spark plug ignites it. You hear pinging or knocking. This can damage an engine.
Lower octane rated fuels can handle the least amount of compression before igniting, higher octane can handle more. It is the compression ratio of an engine that determines the octane rating of the gasoline to be used in that engine.
So if this is true, you could use the lowest octane rated fuel that does not result in knock, in any application, right?
This may not true in all cases, determining knock in a chainsaw may not be as easy as it is in a car, as many things affect what we may or may not perceive as knocking.
With this said, as a precaution, I always use a national brand, high octane gas in all my chainsaws. For a few cents more per gallon, it's cheap insurance.

Not my ideas, but worth reading. I think it came from Madsen's website.

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Mixed Fuel Information

To start, both STIHL and HUSQVARNA recommmend the use of high
octane unleaded gasoline. Both manufacturer's saws are designed to burn
fuel rated at about 90 octane. Most regular grade fuel has an octane
rating of about 87 and won't work well in either brand saw. On the high
end of the spectrum, use of super high octane aviation grade fuel is not
recommended either.

Why does the octane rating of the fuel matter?

Use of a low octane fuel will diminish the power and performance of
your STIHL or HUSQVARNA pro saw. Low octane fuel that works well
in a pick up truck may not work well in a pro saw. Saw powerheads are
high performance engines. They produce more power per pound than
most race car engines. Saw manufacturers use the two-cycle engine
design because it delivers more power per pound than any other type of
piston driven internal combustion engine.

Engine Failure Due to Low Octane Fuel

Low octane fuel used in a STIHL or HUSKY saw may also cause engine
failure. Low octane fuel does not burn properly in the combustion
chamber and may detonate. Detonation can stress internal engine
components and build high heat levels inside an engine. This can lead to
premature bearing failure and piston melt down.

What about the new reformulated fuels?

The Environmental Protection Agency has been involved in changing
gasolines to make them cleaner burning. You have probably heard about
the new "reformulated gasoline" advertised by a number of major oil
companies. These are supposed to produce fewer pollutants and there are
many misconceptions surrounding these reformulated fuels. Here are the
facts as we see them - These new fuels contain chemical additives that
produce oxygen during the combustion process. The additional oxygen
produces a hotter burn which breaks down the compounds in the exhaust
system, producing fewer pollutants. The additional oxygen in the fuel
causes the engine to run lean and hot in comparison to standard
gasolines. Saw engines are designed to withstand the
additional heat that reformulated fuels produce IF they are
properly maintained and the carburetor is properly adjusted.

Our Advice

Since reformulated fuel causes the engine to run lean, you must enrich
the carburetor adjustment on your saw. This means turning the screw out
to increase the fuel portion in the air/fuel mixture. This is especially
important on the high speed adjustment. (See the section on Saw Tuning
& Carburetor Adjustment.)
We usually recommend buying fuel from a reputable fuel distributor
that carries major brands. There is usually someone there that can tell
you about the product you are buying. Cut rate mini marts are potentially
the worst fuel sources. They usually sell the cheapest product available
and employ cashiers who have no idea what kind of fuel they are selling.
If possible, avoid use of reformulated and oxygenated fuels. Also avoid
"gasohol" or gasoline and alcohol mixtures. When these fuels are
impossible to avoid, make sure that your saw is properly adjusted and
that all the cooling fins and passages are clean.

Lots of "old wives tales" being exchanged here. confusion abounds about the difference between detonation and preignition and between a fuels ignitability and its detonation resistance. Take the highest octane fuel you can get and if you run your mixture too lean you will still ruin your two strokes! Unless you really want to make a study of the whole thing, use what the manufacturer recommends; that is guaranteed to work for you. Stay away from screaming lean.
Frank

When I use regular fuel, my pistons melt down quickly,
everytime!
I use 147 octane in competition, and win everytime, the cylinder
is so cool that I have ice to sell at the concession stands.