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

[blsnelling]

Back when I was into quads several years ago, guys were soldering EGT probes into the pipes just after the cylinder. The leaner and hotter the meaner. Same thing should apply here. Here's one I can't answer. If 100LL burns cooler, why can't you just lean it out some more and make even more power? Doesn't a particular fuel have a certain amount of energy per unit? OK, this is getting way over my head.

 

[synness4]

The 115 is green, the really high octane stuff (130) is purple

just my two cents worth the green av gas is 100/130 it's only called 130 because it has extra lead substitute and yes i use 100ll in my saws most of the pump gas is no better than :censored: in your tank ..... 100ll way more lead substitute than your ever gonna need btw they remove fuel from the bottom of the tanks when I pumped av gas years ago rarely was any thing in the "sump" fuel it was called.

 

[deer slayer]

Is there any truth that the oil reduces the octane of the fuel??? I also recently switched, to me better throttle response and as said better shelf life.

 

[blsnelling]

I also found that my saws do not idle near as well with 100LL, very rough. I can't say for sure about the throttle response. I'm afraid this AVGas craze is becoming something like having a Pro or Magnum sticker on your saw. It has to be faster, right?

 

[Buckethead]

Back when I was into quads several years ago, guys were soldering EGT probes into the pipes just after the cylinder. The leaner and hotter the meaner. Same thing should apply here. Here's one I can't answer. If 100LL burns cooler, why can't you just lean it out some more and make even more power? Doesn't a particular fuel have a certain amount of energy per unit? OK, this is getting way over my head.

OUCH...stop it, my brain hurts!

I remember one of our customers had either a CHT or EGT gauge installed in his plane and it made a significant difference in his fuel comsumption. Using the temp gauge he was able to more accurately lean his engine which translated to better range and fuel economy. I want to say he reduced the fuel consumption by about 2-3 GPH...but that was many brain cells ago.

 

[blsnelling]

Makes sense. With accurate information he was able to safely run the engine at a leaner setting, burning less fuel and making more power. Of course you do this without good info and you go too lean and melt the engine down.

 

[Buckethead]

I also found that my saws do not idle near as well with 100LL, very rough. I can't say for sure about the throttle response. I'm afraid this AVGas craze is becoming something like having a Pro or Magnum sticker on your saw. It has to be faster, right?

Interesting observation. My Husky 55 idles great with 100LL. My buddy's 262XP idles like crap on 100LL. Maybe the pro saw are less tolerant??

 

[blsnelling]

Interesting observation. My Husky 55 idles great with 100LL. My buddy's 262XP idles like crap on 100LL. Maybe the pro saw are less tolerant??

You bring up a good point. I didn't notice it so much in like my old Mac 1-52 or David Bradley. It's in my newer saws that I noticed the idle roughly. I finally just decided it wasn't worth it and now only have the 100LL in the oldies. I've never ever had a problem with storage anyway. I actually use the same fuel in my yard equipement that I had in the fall. Never had a problem. All the reading on here tends to make one nervous. I'm really not sure what to believe. Maybe gasoline has changed that much in just the last couple of years. I know before that my 039 would set for months on end and go right back into service without so much as a hickup. Now I "know better", lol

 

[Buckethead]

You bring up a good point. I didn't notice it so much in like my old Mac 1-52 or David Bradley. It's in my newer saws that I noticed the idle roughly. I finally just decided it wasn't worth it and now only have the 100LL in the oldies. I've never ever had a problem with storage anyway. I actually use the same fuel in my yard equipement that I had in the fall. Never had a problem. All the reading on here tends to make one nervous. I'm really not sure what to believe. Maybe gasoline has changed that much in just the last couple of years. I know before that my 039 would set for months on end and go right back into service without so much as a hickup. Now I "know better", lol

So far I've had to "field strip" 4 carbs and remove what looks like "pureed jelly fish" from the bowl and jets. Usually it's raining and I have nothing but a pair of old slip joint pliers, 2 wire strands from a wire brush, and a mostly empty can of carb cleaner. I hate pump gas in small engines.

 

[blsnelling]

I just cleaned the carb in a little cheapie Mac today that belong to a friend. It had that nasty smell and was almost jelly like inside. It riced right off with carb cleaner though. He said it had sat for several years.

 

[Banshee]

100ll was not made for chainsaws. So why is it a surprise when it doesn't make you saw run it's optimum?

It wasn't design to run high rpms. The planes that run it turn something like 2500 rpm's. It was design to run with cold air that you get at high elevations Any where from 20 degrees on down.

It's designed to be light. It lacks heavy burners that you see in pump gas. It does this to save weight. You need both heavy and light for saws. Planes don't really need the heavy burners, but need to save as much weight as possible.

So why use it in your saw. It stores well, mixes better with 2 stroke oils, tolerates high compression better, doesn't build up varnish and deposits as fast and is more resistance to knocking and vapor locking.

The key ingredient for the benefits of av gas is lead, but it has about half the lead (if I remember right) than the lead that was in the leaded gas of the past.

If you wanted the best of both worlds than a mixture of av and pump gas would be a better chainsaw gas. Than just plain av gas.

 

[ShoerFast]

Just another $0.03 cents worth....

First off, I am not sure what that swill is that there selling at the pumps is, but it is not real gas. Anything that burns and can be tested to have a specific octane rating can be sold as pump gas. Higher octane fuels have a better chance of being a better gas to start with, I think that is half the reason more premium blends work better, and not the octane needs?

100LL (100 octane Low Lead) makes it's power and resist preignition by being a very pure form of gas. Pure un-blended gas just burns evenly. Burning evenly and not raising pressures and spontaneously combustion , (preignighting or for the lack of a better word, partly explodes).

Pump gas with additives to control the octane are 'less then' real gas.

I will admit that I am far from understanding what octane modifiers have to do with an engine that is pumping above 10K RPM's and never sees full volumetric efficiencies? But I can see some getting a boost with a more aggressive burning fuel (pump gas).

A couple things Av-gas needs is a low RVP (ried-vapor pressure) to be used at high altitudes, that might be a little harder to get a good eggressive burn at slow speeds (strong idle). And harder to start with a cold engine?
Av-gas is designed for long-stroke 4-cycle engines, it might be a little slow in faster turning engines? (but a real gas is hard to find anymore.

If an engine looses power with Av-gas, I would be hesitant about leaning it to make your heat gains, there is a chance it might come back with just a slightely hotter plug, and could use a slightely more ingition timing to beat the pump fuel in the same engine?
Flame propagation is everything to making power.

Av-gas just plain has more power in it, if you can burn it completely.

A simple test would be to run Av-gas, and again with pump gas with out a muffler, at night, just to piss your neighbors off, and watch for how long the flame cone shoots out the engine?

If there is a lot more cone with 100LL, my bet is that tuning that back to the pump-gas's best, will beat he pump fuel hands down?

Cylinder temp and EGT would be a fun test to use with other ideas, like making the same temp with Av as you got with pump fuel. But a pressure crystal inside the cylinder would be the real instrument.

It is my bet that the pressure comes up a lot slower in a saw that dose not do as well with 100LL ?

A simpler comparison would be summer - winter power gains comparing fuels.

 

[Highclimber OR]

My buddy and I use 110 octane no ethanol fuel in our saws and have no issues. The only thing is that you should tune for it and everything will be fine.

 

[Outlaw5.0]

I use 100 octane unleaded racing gas in my one MS460, it has 200-205 psi cylinder pressure. All my other saws get 92-94 octane premium with stabil. I have also 50/50 mixed 100 octane unleaded/87 octane pump together which worked good. The reason for mixing was shelf life.

 

[jburlingham]

Brad,

If I were to try gathering some operating temp data for pump gas vs. Avgas would it be better to look at exhaust gas temp. or cylinder temp.??

Search the site, there was a link to an EPA study on this, the more ethanol the hotter the equipment ran and shorter the life it had.

 

[MCW]

I'm certainly no expert when it comes to 2 strokes but I know that by using higher octane fuel in a standard old school car motor you'll make no extra power. Newer engines though with knock sensors WILL make more power if going from 91 octane unleaded to 98 octane unleaded by automatically advancing the timing.
A previous car I had (R31 Australian Built Nissan Skyline - 3.0L 6 cylinder) made more power and had nearly 10% better fuel economy when I advanced the timing from 15° to 20° and went from 91 to 98 octane fuel. I could not run 91 octane at 20° though as it would ping (knock) under load.
With a 2 stroke motor with no mods I doubt whether the extra octane is useful (although I do use 98 octane premium unleaded in all my saws - I think it gives you a buffer if the saw starts to lean out and its also higher quality fuel made to better standards). I'm sure though if you tuned your saw to suit higher octane fuels you'd make more power, not 100% certain, but pretty sure you would.
This is definately the case in 4 stroke engines, particularly turbos.

 

[blsnelling]

I'm not into removing the flywheel key and playing with the timing, but maybe that's what it would take to really take advantage of 100LL. Someone mentioned that it's slower burning and is kind of like retarding the timing. Advance the timing and start it burning sooner and maybe you'd have something. I'll leave that for someone else to test.

 

[MCW]

I'm not into removing the flywheel key and playing with the timing, but maybe that's what it would take to really take advantage of 100LL. Someone mentioned that it's slower burning and is kind of like retarding the timing. Advance the timing and start it burning sooner and maybe you'd have something. I'll leave that for someone else to test.

Yeah I agree Brad. In theory higher octane fuel should be able to make more power if you advance the timing but like you mentioned it wouldn't be an easy task on a chainsaw

 

[blsnelling]

Yeah I agree Brad. In theory higher octane fuel should be able to make more power if you advance the timing but like you mentioned it wouldn't be an easy task on a chainsaw

Too bad the coil's not mounted on a slottable plate like my Yamaha Banshee was.

 

[PA Plumber]

I have noticed all of my saws idle better on 100LL than the ethanol blend found at the pump.

Maybe I'm just now learning how to tune!?!