the great oil debate

[SIRCHOPALOT]

I have seen many posts on this subject, and it totally baffles me.: 32/1 or 50/1 or 100/1. all I want to know is why in the wide world of sports would anyone ever want to run 100/1 mix in a saw? or 75/1 for that matter? what is the purpose? I have seen arguements that 50/1 ratios produce less heat than a 32/1 ratio. thats totally goofy. I think I will do a dyno run at 32/1 and at 50/1 and post the results, so everyone can see that there is no difference in power. (or so little that you would never know) and I guarantee that a saw at 32/1 will live longer than a saw at 75/1. so please post why you want to run so little oil. I would love to hear the reasons.

 

[Marco]

emissions, that's what we're told

 

[Lobo]

I have seen arguements that 50/1 ratios produce less heat than a 32/1 ratio. thats totally goofy. I think I will do a dyno run at 32/1 and at 50/1 and post the results, so everyone can see that there is no difference in power.

I would definitely love bench heat and hp test to be run as well and the results quantified. I wonder if heat tests could be run off the bench also in real time use while cutting in something like a 10 or 12 inch log with the same power units,oils and same ratios, something like 32:1 - 50:1 - 75:1 - 100:1

That would probably straighten out this never ending debate for a while.

 

[VTMechEng]

Theoretically there should be some power loss with a 32:1 over 50:1 and it is very easy to see why. Gas is what causes the explosion, causing the gasses to expand at a rapid rate and forcing the piston down. While oil does burn it will not burn as hot, clean, or fast which is why we need the gas in there to begin with. By adding the extra oil for a 32:1 mix you are adding 36% more oil or 36% less gass to combust. End result, run what the owners manual says to (it doesn't hurt to have a little extra oil though, but just a little)

 

[Erik D. Schmid]

I run all of mine anywhere from 45:1 to 50:1 using Amsoil Saber 100:1 pre-mix. I do so because that is what Stihl recommends. They test their saws at either 70:1 or 80:1. I can't remember which right now. So, I see no problem with doing what they say. I trust their knowledge on the subject.

 

[DirtTroll]

Look at the fuel like the powders used in bullets. Pistols need faster burning powders and rifles slower. Guns like engines are all based upon their expansion chambers. Small expansion needs fast burning while large expansion can take advantage of the slower burning. The is more energy in the slower burning powders and fuels but it does you no good unless you can take advantage of it. For instance the cetane rating (energy available per volume) for diesel is higher than gas but burns much slower.

Low RPM (150 to 200 rpm) ships diesels burn straight oil that comes close to the consistancy of TAR because it is more efficient, but they have very long strokes with huge expansion chambers. 2 cycle chainsaws by their very nature have very small expansion chambers.

 

[VTMechEng]

DirtTroll, are you saying to add less or more oil? I understand and fully agree with that you are saying but have missed your point. I am assuming you say go with the 50:1 because it will allow for more fast burning fuel.

 

[DirtTroll]

I personnally run 40-1 ratio. What very little I give up in performance I hopefully recapture in lubrication. Going to a higher ration 32 or 40 to 1 is not a good idea with the newer saws though unless you gut the muffler and remove alot of the back pressure.

The newer saws are reverse scavenging with the tighter mufflers to cut down on emmisions and the extra oil will create hot spots in the cylinder wall due to that there is more engergy available for burning in oil versus gas. I gutted my mufflers and run higher ratio's like the older style saws. Ever notice the old saws rarely wear out?

 

[Lobo]

I think the one point not being mentioned is that todays oils + additive packages are so superior to oils of 25 - 30 - 35 years ago (I am talking Dino oils here not necessarily syns which IMHO are another improvement).
Metallurgy has improved significantly also over the same period of time.

 

[Blowdown1]

By adding the extra oil for a 32:1 mix you are adding 36% more oil or 36% less gass to combust.

No, you are not decreasing gas by the same (36%). That would only be the case if you were using equal amounts of fuel and oil.

And you are actually increasing oil by 56% by going from 50:1 to 32:1 (if I have done my math right, which is not guaranteed). You are calculating the % change in ratio, not actual quantity.

the decrease in available gas for combustion is a little over 1% (again, provided I did my math correctly).

 

[Jackman61]

Don't get a headache over the math because at 32:1 the high speed jet will be open more than at 100:1. The fuel per unit volume will change, the air to fuel mixture will have to stay the same to make a valid performance comparison.

No matter what the oil bottle label claims, IMHO 100:1 is taking it too far. 40-50:1 will be here to stay for emissions purposes with acceptable longevity (thanks to better quality oil than the 16:1 time frame). If the adjustability is available in the carb, increase the oil ratio (more oil) to make yourself feel better.

 

[Elmore]

Power

I've recently read, somewhere on the "net', that a higher concentration of oil in a mix resulted in more power. Just my two cents.

 

[VTMechEng]

Here is a more complex way of calculating but the answer is really close to the same. Because the amount of mix you are making must be constant, as you increase the amount of oil you also decrease the amount of gas. As a result (and I can show how I got these but who really wants to see all that crap, you probably don't want to even see this hehe) the following equations can be used:
y = T / (R+1)
x = T - y
Where 'y' is the amount of oil, 'x' is the amount of gas, 'T' is the total amount of mixture desired, and 'R' is the ratio (the 50 in 50:1 or 32 in 32:1). As an example lets calculate the percent decrease in oil from 32:1 to 50:1 in 2 gal. of mixture.
T = 2; R = 32;
y = 2 / (32+1) = .061 gal.
x = 2 - .061 = 1.940 gal.

T = 2; R = 50;
y = 2 / (50+1) = .039 gal.
x = 2 - = 1.961 gal.

Difference = .022 gal of oil
Percent decrease = 36.01%

 

[Blowdown1]

VT Eng, what would be the decrease in gas if you dropped to 25:1 ratio?

Let me guess 50%?

 

[brent denny]

Jackman61, your last post sums up exactly how I feel after agonizing over ratios and oil ever since I started reading oil threads on this forum.

 

[Lewis Brander]

Oil/Fuel mix and Air:

Ok, I'm no engineer, but here goes. The last I knew was that the ideal air to fuel ratio was 14.7 to 1 for proper combustion and efficiency. If you add oil to the fuel you still have to maintain the proper air/fuel ratio. The oil being the variable here means, that if you are running more oil you have to open the jets/ metering rods in the carb to maintain the right air/ fuel ratio. If you have a saw running 50/1 mix and adjust the carb for best engine performance then change the mix to say 32/1 mix through the same carb settings the air fuel ratio is leaner. Thus you have to open the carb settings to maintain the right air fuel ratio for porper perfromance. As far as I can see the engine would run at approximately the same temperature due to the evaporational cooling effect of the fuel if the 14.7/1 air fuel ratio is maintained. To have combustion you need air and fuel mixed at the right ratio. You add oil to the fuel and you have say a lean conditon that has to be taken care of by enrichening the carb to maintain the right air/fuel ratio. The reverse is true if you are running a 32/1 mix of fuel and adjust the carb for that. When you change to say 50/1 mix, there is less oil, so therefore a richer mixture and the carb has to be leaned down to maintain the right Air/ Fuel ratio and proper performance. Does this make any sence? I've run fuel/oil mixes from 16/1 to 40/1 through my saws. The richer the oil in the fuel (16/1 mix) the leaner the air/fuel rato and consequently I have to open the carb adjustment a bit to maintain proper performance. For the same carb settings going to a mix of say 40/1 there is more fuel and usually have to lean the carb a bit. OK, probably got this all screwed up, but JMO. Like I said I'm no engineer, I don't own a dyno or modify any saws so what do you think of my ramblings. Everyone take care. Lewis.

 

[SIRCHOPALOT]

Don't get a headache over the math because at 32:1 the high speed jet will be open more than at 100:1. The fuel per unit volume will change, the air to fuel mixture will have to stay the same to make a valid performance comparison.

No matter what the oil bottle label claims, IMHO 100:1 is taking it too far. 40-50:1 will be here to stay for emissions purposes with acceptable longevity (thanks to better quality oil than the 16:1 time frame). If the adjustability is available in the carb, increase the oil ratio (more oil) to make yourself feel better.

exactly. glad to see someone has some sense.

 

[tony marks]

ive found no peceptable drop in power since going to 32-1 with mobile mx2t..
it just runs good.. no problems.. actually had no problems with stihl or husky dino at 50-1.. im just hedging my bet a bit..
2 cycles like trimmrs an such dont put the kind of a load that chainsaws do .. i wouldnt runun my 3 good saws at 100-1 with any miracle oil.. just aint a chance im taking with saws that are exactly to my liking.. jmo

 

[weimedog]

You can over analyze anything. Fact is you jet to the conditions at hand (when tuning a race bike or a saw), so when you change the oil ratio you also need to jet to the new fuel situation to optimize performance....so you can spend all the time calculating and rationalizing to come up with any conclusions you want on paper..but a properly jetted saw running a new generation synthetic at 32:1 is going to run well for a long time. Same with two stroke motorcycles.

One difference with race saws vs. race motorcycles is the period of time the thing has to run! Also race saws probably don't do anything but run flat out for that short time they are running. Never heard of an endurance saw race (although a few pictures were posted a few months back of sectioning logs down under when we were discussing chain saw milling as a test of saw power) Point being using peak power arguements that might be interesting to a race saw type isn't as interesting to a pro or even a casual saw user.

One of the reasons many of us went to the 32-38:1 mixtures was we found over the duration of a race there was less heat build up in our motors (and yes we tested with heat tape and later with temp guns) than with the 45-50:1 mixes. You might argue there might be a slight loss of power (debateable at best with proper jetting) but having a more steady state heat situation over a race period meant at the end of a race the motor was putting out the same type of power as in the beginning. (Heat changes also meant tolerance changes which has impact on power) (Water cooling gave a lot more latitude in tuning with mixtures, compression, and timing than the air coolers had) I also saw a different in rod-wrist & bottom end bearing life over a race season with the different mixtures...yet another reason MANY went to the richer (32-36-38:1) oil mixtures. My bet is the typical saw owner is a whole lot more interested in component life than a bunch of mumbo jumbo trying to rationalize how you might get a few more percentage points more fuel usage, power or anything else.

Seems you can go to any motorsports website and forum and find a thread or two in-process about synthetic oils. Usually started with someone questioning Amzoil claims.

 

[Lobo]

You know its curious you here an awful lot of people questioning, debating and ridiculing Amsoil and their claims and statements, however contrary to all the other products such as Slick 50, STP, Dura-lube, etc. who have lost law suits or had their fingers rapped by the feds, I have never heard or come across such items on Amsoil.

Are there any?