High octane gas

[mountain_man]

Something else that may perhaps change a few things? CR125 don't run at 15k RPM like some race saws? I don't know true RPM's but they probably need a little more oil in the mix.

 

[Wood Doctor]

LOML refuses to put anything but high octane premium fuel in her 1991 Toyota Celica GTS. I figure that if she can put that good stuff in the car, I can mix synthetic and put the same gas in my Stihl MS 361's tank. What's good enough for the goose is good enough for the gander. Heheheheh.:greenchainsaw:

 

[wood4heat]

Something else that may perhaps change a few things? CR125 don't run at 15k RPM like some race saws? I don't know true RPM's but they probably need a little more oil in the mix.

They'll run around 13,000. The guys using them for cart motors get 15,000 out of them down the straits. The cart guys will actually reach back and lean them out to get a couple hundred extra rpm down the straits! They also run castor oils and re ring them every weekend.

 

[mjbilbo]

so it is looking like a mix of 3 oz per gallon of Stihl Ultra or Mobil 1 2T with at least 89 octane fuel is a good place to go?

 

[Crofter]

Quote:
Originally Posted by B_Turner View Post
To be a smart azz, that is not true with newer generation auto motors with variable valve and ignition timings.

It's absolutely true especially with modern engines. They're designed to run in a certain octane range and would run like cr@p if you got out of it whether above or below.

The new generation four stroke mx bikes tell you NOT to run race gas in them. They run like **** on it unless you modify them.

I think B_Turner is on the money here. Couldnt tell you a thing about the mx bikes though.
Modern auto engines have computer controlled management of quite a few engine adjustments that allow the use of a wider range of fuel octane properties. The major one being knock sensors that detect incipient detonation and vary ignition timing to adjust for engines instantaneous octane requirements. Air fuel ratio is under its control also. Unless you choose a fuel that is totally outside normal octane parameters it will burn it optimally. You really have to study the particular blend of gasoline to see what its energy content is to be able to predict which one would give a slight edge in such a computer managed engine. It is not a hard and fast rule that higher octane relates to lower BTU content. It is generally true though that a fuel will burn most efficiently if it is operating close to its detonation limits. It then also has virtually no safety margin to prevent damage if some stray cause like a plugged filter or dirty cooling fins etc. raises the engines octane requirements. While a saw may show slightly higher performance(if very accurately measured) with the lower octane fuel, you could quite likely make adjustments with the higher octane fuel that would allow performance higher than you could get under any circumstances with the lower octane fuel.
It simply isnt just that simple to get a short answer.

 

[wood4heat]

Quote:
Originally Posted by B_Turner View Post
To be a smart azz, that is not true with newer generation auto motors with variable valve and ignition timings.




I think B_Turner is on the money here. Couldnt tell you a thing about the mx bikes though.
Modern auto engines have computer controlled management of quite a few engine adjustments that allow the use of a wider range of fuel octane properties. The major one being knock sensors that detect incipient detonation and vary ignition timing to adjust for engines instantaneous octane requirements. Air fuel ratio is under its control also. Unless you choose a fuel that is totally outside normal octane parameters it will burn it optimally. You really have to study the particular blend of gasoline to see what its energy content is to be able to predict which one would give a slight edge in such a computer managed engine. It is not a hard and fast rule that higher octane relates to lower BTU content. It is generally true though that a fuel will burn most efficiently if it is operating close to its detonation limits. It then also has virtually no safety margin to prevent damage if some stray cause like a plugged filter or dirty cooling fins etc. raises the engines octane requirements. While a saw may show slightly higher performance(if very accurately measured) with the lower octane fuel, you could quite likely make adjustments with the higher octane fuel that would allow performance higher than you could get under any circumstances with the lower octane fuel.
It simply isnt just that simple to get a short answer.

I still disagree, all the engine managment controls you mentioned are designed to make the most of lower octane fuels not to take advantage of race gas.

Ok after rereading the whole thread I apologize B_turner. I had race gas in my head the first time through and now realize you were talking regular vs super. I agree with your original post that either of those fall in to the octane range a modern engine could take advantage of.

 

[Crofter]

Here is a snip about energy content of regular VS premium gasoline. It appears that the higher octane gasoline may have a lower flame front speed if it is not adequately compressed and this can reflect in reduced output if ignition timing is not advanced to compensate. I cant find it at the moment but I think there are high octane specialty fuels that do not have a lower burning rate. Two different blends of gasoline with the same octane rating may have slightly different performance characteristics.

Q heating value of fuel, i.e. the energy released when a given mass of fuel is burned. Q is varies slightly with different grades of gasoline (regular 87 octane is about 42.7 MJ/kg, premium is about 43.5 MJ/kg, and fuels blended with high levels of MTBE and/or ethanol have lower heating values).

The whole article is a good read on engine tuning and octane requirements.

http://www.daytona-sensors.com/tech_tuning.html

 

[wood4heat]

Here is a snip about energy content of regular VS premium gasoline. It appears that the higher octane gasoline may have a lower flame front speed if it is not adequately compressed and this can reflect in reduced output if ignition timing is not advanced to compensate. I cant find it at the moment but I think there are high octane specialty fuels that do not have a lower burning rate. Two different blends of gasoline with the same octane rating may have slightly different performance characteristics.

Q heating value of fuel, i.e. the energy released when a given mass of fuel is burned. Q is varies slightly with different grades of gasoline (regular 87 octane is about 42.7 MJ/kg, premium is about 43.5 MJ/kg, and fuels blended with high levels of MTBE and/or ethanol have lower heating values).

The whole article is a good read on engine tuning and octane requirements.

http://www.daytona-sensors.com/tech_tuning.html

Here is another good link:

http://www.vpracingfuels.com/vp_fuelprop.html

I have run a lot of race fuels in my bikes and VP C12 was the best. Burns cool, clean, and crisp.

 

[wkpoor]

Been using AvGas for yrs now in my 2 stroker engines. Haven't seen any adverse effects. I mainly use it because it doesn't go stale. To me its just like a can of lacquer thinner. It never goes bad just dries up reel fast.

 

[24d]

Blue gas and bean oil, its worth it for the smell if nutin else

 

[timberwolf]

Spent the whole day breathing blue gas and bean oil fumes. Same stuff woodheat was talking about. LOL

All was good with the blue gas until as started playing with mixing in with more and more pinky orange fuel, then the problems started, now I am redesigning my carberator to work with pinky orange fuel.

 

[wood4heat]

Spent the whole day breathing blue gas and bean oil fumes. Same stuff woodheat was talking about. LOL

All was good with the blue gas until as started playing with mixing in with more and more pinky orange fuel, then the problems started, now I am redesigning my carberator to work with pinky orange fuel.

What are you working on?

 

[Crofter]

http://www.youtube.com/watch?v=sIbwQK_jr-I

Here it is still on gasoline.

 

[timberwolf]

372 BB cut off head, running blue fuel here, not pink stuff. I didn't get into videos with pink stuff, still was having too many problems with mixture to bother with a camera on top of the saw.

 

[foxeye]

My MS270 manual states to use mid grade 89 octane and if unavailable to go with higher octane. Makes no mention on usuing nay 87 or lower octane fuels. Ever since I can remember I have always used premium syn or dino oils and high octane gas and have never really had any related problems from such. Madsens on line at one time had a good article that expained it all very very clearly and simple...and basically stated use high octane in all 2 strokes and do not worry about it that your motor weill thank you for it.

 

[timberwolf]

The difference between 87 and 89 at the pumps may be almost exactly nothing. Gas formulations are different one batch of fuel to the next, one brand to the next. 87 octane gas is not going to harm a stock chainsaw. But as fuel ages the octane may drop, add poor quality oil and the octane may drop, put the lowest grade fuel together with crap oil and wait six months and certainly it's doing the engine no favors.

 

[24d]

Brian,

I read somewhere avgas can be stored longer than pump gas and any gas will hold up better with no oil in it. Thoughts?

Later,

 

[Lakeside53]

avgas is good for year or two.... but.. why bother storing it! Use it, or get it out of the saw/whatever.

 

[bwalker]

This thread has so much mis information in it that it should be deleted for the common good.

 

[Lakeside53]

HUH? What have you done with Ben?

The Ben I once knew would have been correcting the misnomers post by post:greenchainsaw: