100 octane gas will "burn up" saw???

[Kemper]

I've got a landscaper guy telling me that the 100 octane "jet fuel" that I'm running will burn up my saws. I don't understand how this could be, but I wanted to run it by you guys just to be safe. The only reason I buy 100 is to get actual gasoline and not ethanol. Is there any way excessive octane could hurt an engine? I mean the answer has to be "no" right?

(By the way, I didn't bother to explain to this guy that Jet A is nothing more than glorified kerosene)

My kids ran it in their dirt bikes for years, they will actually run cooler.

 

[Meadow Beaver]

I've got a landscaper guy telling me that the 100 octane "jet fuel" that I'm running will burn up my saws. I don't understand how this could be, but I wanted to run it by you guys just to be safe. The only reason I buy 100 is to get actual gasoline and not ethanol. Is there any way excessive octane could hurt an engine? I mean the answer has to be "no" right?

(By the way, I didn't bother to explain to this guy that Jet A is nothing more than glorified kerosene)

That's bull, one of my friends runs 114 octane only in his saws and has never had a problem.

 

[eichhoma]

There is a gas statioon not far from me that sells 110 Octane leaded "race fuel".... is that basically av fuel? this whole gas thing kind of has me confused. I assume it is safe to run that in everything? It does not contain ethanol, so that has to be good right? what about the lead? thanks!

 

[blsnelling]

I'm going to guess that 100LL is significantly different than high octane race gas. Anyone know.

 

[Crofter]

There are threads in the archives that have discussed this issue in more depth.

Couple of things. Carb icing is a heavy issue with aviation fuel and there will most likely be a difference in evaporative cooling than pump gas; this could well have an effect on idle in a chain saw and depend from one to the other how much insulation the carb has from the crankcase (carb heat) has an effect on mixture adj. Fuel vapor pressure as Shoer mentions is also an issue, as you dont want loss of lighter components at high elevations or in storage. Pump gas is more a soup of more and less volatile components to average out to what is seasonally considered adequate. Not really an issue for a saw but could have an effect on how you tune.

Gasoline and almost any other fuel that I can think of will burn more efficiently (convert more of its inherent BTU content to heat) the closer it is to its detonation point. Octane rating is a measure of resistance to detonation (not pre ignition) On average there is no difference in BTU content of various octane rated fuels but the higher rated ones can operate with a combination of, earlier ignition timing, higher charge temperatures, combustion chamber temperatures and compression.
If an engine was being operated lean enough on low octane fuel to be causing high head and piston temperatures by being into the initial stages of detonation then a higher octane fuel would lower combustion chamber temperatures. I think you will find that either one will have the same burning temperature if tuning is right to keep it just short of detonation. I think if you research actual flame propagation rates you will see there is no relation to octane rating either. Dont try to get a short answer out of visiting the web sites of some of the specialty fuel suppliers. Each one is better than the others and will claim to make you a winner. If your saw is built and tuned for it you will be able to get higher output from higher octane gasoline, but if it is not, you could well get higher output from a lower octane fuel.

I think Shoer also mentioned design operating rpm and stroke length of an aero engine vs a saw enginge. This has a very large influence on the length of time of the combustion event. The onset of detonation has a time factor as well as a pressure factor in what triggers it. Time related breakdown into detonation sensitive components of the burning fuel charge is not nearly as important a factor in a high rpm engine so there is not the need for the higher octane for a chainsaw, and unless someone goes to considerable pains to get the compression in a saw up in the range of 225 psi or relocate the fixed ignition timing much advanced, a saw wont have pressure induced high octane fuel requirements either.

Aviation fuel of the same octane rating as an auto race fuel could have considerably different characteristics in the carburetor of a chainsaw and neither one would be designed for best performance for a crankcase scavenged two stroke that has a fair bit of its piston cooling done by the fuel.

Any of the specialty fuels will have a much better stability rating and virtually no variation from one tankfull to the next that you get with the crapshoot at the pumps but there are a lot of contradicting factors for using it in chainsaws and dont bet the rent money on either one winning or losing a race for you unless the particular engine is tuned for the particular fuel.

 

[Meadow Beaver]

My friend who uses 114 uses it for pulling trucks and chainsaws, not racing or flying planes.

 

[thejdman04]

It wont burn up you saw.

 

[Meadow Beaver]

Not as long as you put the mix in, then your fine. It will actually run a little better.

 

[JONSEREDFAN6069]

i was running VP c-10 fuel it's unleaded non-oxygenated (no ethenol) research octane is 104 motor octane is 99 and is crystal clear. it still smell's good almost like the u4.2 leaded i'm running now as it's designed for stock or modified 2 or 4 stroke engines and makes 6% more power than pump gas. motor octane is 104 only draw back is it's oxygenated (has ethenol) but seems to stay good longer if kept in the tin it comes in for some reason. of course i'm quoting the VP website but the u4.2 is FASTER in timed cut's than 91 octane premium. is it more expensive? yes. does it keep better? yes.
will it burn up a engine? absolutely not!!!!! does it increase performance? ABSOLUTELY!!!!!!!!!!!

 

[Meadow Beaver]

Besides the higher the octane the better it burns, so why stay with 91.

 

[tree MDS]

Wow! You saw heads are hardcore, thats for sure.

I'd better unsubscribe from this one or I'll be getting e mails on this a year from now. lol

 

[demographic]

I am not a mechanic or anything but I would have to argue Av gas making them slower. Why would they run high octane fuel in race bikes (motocross), atleast they did before the 4 stroke era. If they can design $100,000 race bikes, I doubt they are lacking the knowlege about proper fuel.

This article might interest you...

AVGas: The Truth
Posted by Rich Rohrich
Posted 04-21-2005


An excerpt from Fuel for Thought - Part 2
by Rich Rohrich



The Avgas question comes up all the time and there are a huge number of silly myths associated with it.



To the question will Avgas hurt my engine?

The simple answer is 100LL Avgas usually isn’t the best choice but it won't hurt anything. 100LL (Blue) Avgas seems to be the most readily available version so that's what we'll concentrate on.


For general high speed purposes Avgas has a couple of problems:

1) The 90% distillation point for 100LL Blue Avgas is set at 275 degrees F and the end point is set at 338F, which in an engine that turns over 7000 rpm will likely make less power than a fuel that has it's 90% point lower. Pump gas has similar problems, but most good race gas will have 90% Point MUCH lower. As an example VP C12 has a 90% distillation point around 228F and an end point set at 233.3F.



2) Depending on the refiner 100LL can have fairly high aromatic hydrocarbon content, in the 30% by weight range. This level of aromatics will tend to make the throttle response mushy and flat in applications that see big throttle opening transitions on a regular basis. It's similar to what happens when you dump a lot of Toluene based octane booster in your fuel. Throttle response becomes a distant memory.



3) The vapor pressure and distillation curve of Avgas just isn’t right for many applications. The distillation curve or Volatility curve of a fuel determines to a large degree the warm-up, transitional (on & off) throttle response, and acceleration characteristics of an engine.

Here's the simplified version:

A fuels distillation curve designates the maximum temperatures at which various points between 10% and 90% of the fuel will be evaporated as well as the maximum end point temperature. So for any Engine/Air Temperature combination there is a minimum volatility that is required for proper running. As you probably know gasoline is made up of different hydrocarbons, with different distillation points. By combining these Hydrocarbons together you get a Distillation/Volatility curve. Some hydrocarbons (light ends) boil off at low temps some at much higher temps. Depending on the intended application, a petrochemist will blend hydrocarbons to get a curve that matches the rpm range, temp, altitude, and acceleration characteristics for the application. The problem with avgas as a race fuel is the fact it is blended for an application where acceleration and throttle response is not a high priority. If you think about the average light airplane application, you're talking about a fairly low compression engine that runs in a fairly narrow rpm band, and is rarely called on to provide the type of transitional throttle response that a high rpm, acceleration critical application like motocross does. What's more important to the Avgas designer is controlling mixture strength by eliminating the possibility of vapor lock and making sure that light end hydrocarbon fractions don't boil off too early, and the lowered rpm ranges allow them to push the distillation point up on the upper end as well. As you can see, by using straight Avgas or by mixing various types of fuel together you are modifying a number of important fuel design parameters. You may hit on a combination that works well, but more likely you'll have an engine that doesn't detonate, but doesn't accelerate very well either. So Avgas is SAFE, but not a very good choice. The high paraffinic hydrocarbon content of 100LL makes a very good base stock if you want to play back yard petrochemist, and I believe this is how some of the smaller race fuel blenders start out. I can tell you from experience that it's a bear to document and test various changes unless you have a lot of time and patience, so trying to come up with your own Super Fuel is probably more trouble than it is worth.



So it sounds like Avgas is really bad for our purposes, and for the most part it is, but there is a possible exception. The closer you get to the thermal limits of a particular engine design the more useful Avgas becomes. The end point distillation temperature of Avgas is high enough that some of the fuel can make its way into the combustion chamber in liquid form. While this would normally prove to be a liability in most engines it could be useful when you are tuning to the ragged edge. The liquid fuel droplets entering the combustion chamber will leech some heat and help to cool the piston crown. In an engine that is pushing the thermal limits this can be the difference between a win and a holed piston. Some specialty karting fuels like Philips P45 are designed with a large jump at the end of the distillation curve to specifically provide this cooling effect. It’s not uncommon for a fuel with higher octane than Avgas but lower end point temperatures to experience preignition problems long before Avgas. It's the tuning equivalent of making lemonade out of lemons. For engine combinations that aren't near their thermal limits like MX applications this high end temperature just ends up as oil spooge dripping out of the silencer even when the jetting is lean. As I've pointed out time and again, the octane rating of a fuel is just one part of the tuning equation.

The sad fact is given the sorry state of pump fuel today Avgas is looking better all the time even when you aren't pushing the thermal limits.
Here's my short course take on things based on my experience and personal biases, (keep in mind this is pretty generalized)

- In almost every case 100ll Avgas is a better choice than alcohol pump fuels.

- If you don't need the additional octane that 100LL provides, then MTBE based pump premium will tend to provide better throttle than Avgas assuming you have any jetting skill. If you can't jet you're just wasting your time worrying about any of this stuff on a stock bike.

- Mixing 100LL Avgas with a good race gas designed for your application and rpm range is a reasonable way to save some money.

- Mixing alcohol based pump fuels with ANYTHING in an attempt to make it BETTER is just a chemical circle jerk, and if you're that cheap or that ignorant you deserve the crummy performance and the insurmountable jetting problems that you will invariably be blessed with.

- Milspec Avgas is a different animal entirely, but isn't readily available so we won't worry about it.

- If you are running near the thermal limits of your engine combination Avgas may provide a margin of safety that isn't available even in a high-octane fuel with a flat fuel curve.

- The correct race fuel for your application will outperform ANY of the above, regardless of whether the engine is stock or modified. The more demon tweaks hiding in your engine, the more you have to gain.

 

[blsnelling]

Thanks for posting Crofter. I was hoping someone such as yourself would tune in.

 

[blsnelling]

Demographic, thanks so much for posting that. The guy that wrote that article has the scientific knowledge to explain what I've been experiencing. Obviously, there's a lot more to fuel than octane rating. I've experienced most if not all of the problems talked about in this thread. I only started using 100LL in early January. In that short amount of time I have experienced: less performance, poor idling and throttle response, and multiple carb icing occurences which I had never experienced before. All of this started when I went to 100LL and went away when I quit using it. People need to start thinking for themselves instead of just going on a whim or misconceived perception. Make your own decisions based on your experiences and the facts that are available.

Sounds like if you want improved storability and performance at least equal to pump gas, you'll have to find the right race gas. 100LL isn't it.

 

[Crofter]

Demographic, thanks so much for posting that. The guy that wrote that article has the scientific knowledge to explain what I've been experiencing. Obviously, there's a lot more to fuel than octane rating. ,<SNIP>.

Yes!
That article sounds like something you can take to the bank! There are lots of articles on the net that have a lot of advertising spin or out of context results you cant generalize to be true for your application; also there sure is a lot of stuff on the web that is well meaning but simply not correct at all.

 

[flyboy]

You say you want my pistons hitting the cylinder head?

100LL has its place. I actually have several gallons here. I can think of a couple good reasons to use it. First, extended storage. I have 100LL in my old saws that will see liitle to no regular use. They may come out a couple times a year for GTG fun. Second, if you have an all out race saw with well over 200 PSI compression. How high I don't know. I've had more than one saw with 190 PSI that was fine on premium gasoline. Other than that, I can't think of any reasons that you would want to run 100LL.

For a not so close reference. BMW claims my 325 was 10.5:1 compression and needed 91+ octane. At 190k miles each cylinder was reading 195 psi.

My understanding is air cooled motors have to be quite a bit more sloppy than liquid because they have a much wider operating range for temperature.

 

[BuddhaKat]

I Googled the author of the article posted by demographic and got this link: http://www.polariswatercraft.com.au/fuelforthought.htm

I think it's part 1 of the article. Extremely interesting reading. This guy knows his stuff.

 

[demographic]

My understanding is air cooled motors have to be quite a bit more sloppy than liquid because they have a much wider operating range for temperature.

That goes along with the stuff I have read in two stroke motorcycle tuning books as well.

 

[PA Plumber]

~snip~

Sounds like if you want improved storability and performance at least equal to pump gas, you'll have to find the right race gas. 100LL isn't it.

Since I'm not planning on going into petrol-chemistry, I'll stick with the 100LL.

Still sounds like it is better than the current pump gas that is available.

 

[JONSEREDFAN6069]

wow ppl seem to wanna argue for the sake of arguing. if you think it runs better than pump gas run it. i know my race gas makes my saw run better but i know some ppl will tell me it's in my head. the fuel i'm running is formulated to run either stock or modded with little to no carb changes. it's
awesome stuff.