Oil Mix Ratios and Cylinder Head Temperatures

[bwalker]

Just throwing out a few factiods here:
1). gasoline has about 18,800 BTUs per pound.
2). Ethyl alcohol has 13,000 BTUs per pound.
3). lube oil has quite a bit more latent heat energy than gasoline- I'd guess around 20,000 BTUs per pound.
4). "octane rating" has to do with the speed in which combustion propagates (the rate combustion spreads from molecule to molecule). In a recip engine this is usually said to be 90 feet per second from the point of ignition in normal combustion. Propagation during detonation or "knock" is a lot faster (and HOTTER!). In the old days, they expressed the resistance of a fuel to pre ignition by comparing it to a fuel made up of a ratio of iso octane (which was at that time the most pre ignition-resistant fuel known) to normal heptane (which was about 100% pre-ignition). So, a fuel with an octane rating of 87 would behave the same as a mixture of 87 iso octane and 13% normal heptane. This is why "octane" only goes to 100. For anything higher, resistance to pre-ignition is expressed by "performance number". Octane has nothing to do with latent heat value.

Soooo..... having hard numbers to work with a number of conclusions can be drawn. If you cut 18,800 BTU gas 10-15% with 13,000 BTU alcohol, the result will be a fuel with less BTU value than gasoline- iE: less heat energy available. If all else remains the same, combustion temps will be lower.

Lube oil burns hotter than gas- but the difference between 50:1 (2% oil) and 32:1 (3% oil) isn't all that much. You can do the math and get a good idea what the final effect on combustion temp will be.

Burn speed will be effected by both octane rating and mixture. If the fuel/air mix burns slower, there will be less heat absorbed my the cylinder wall and head, and more downstream by the exhaust port and muffler, given the ignition timing remains the same. This will effect the EGT (greatly!).

Octane rating, since it controls the spread of combustion between molecules, has an effect on burn speed, which has an effect on where in the process combustion happens- in the cylinder or in the muffler.

Sorry for the long winded presentation- I had to know all this stuff to get my Aircraft Mechanics licences 40 years ago.

Porosonik.

Burn speed has nothing to do with octane.

 

[rogue60]

Fuel is that good nowadays you don't need to add oil try it you will be amazed at the results..

 

[Jonny Quest]

Fuel is that good nowadays you don't need to add oil try it you will be amazed at the results..

It's those pesky fuel additives...
My new 2 cycle oil of choice is Marvel Mystery Oil.

JQ

 

[lone wolf]

It's those pesky fuel additives...
My new 2 cycle oil of choice is Marvel Mystery Oil.

JQ

My buddy ran ATF in his Hoodaka Combat Wombat. Never seized.

 

[Jonny Quest]

Hodaka Combat Wombat! That's a name I've not heard in a long time...Back in the day, my buddy owned a 1973 Combat Wombat. I think it was 125cc. Dang. Memory lane...

JQ

 

[Husky77]

A good thread, this could go on until christmas
I only use Aspen2 in the past I spend years trying this and that oil, what is better what is not so good. I tried stihl ultra with Aspen4 thats very clean too, worked out a lot more expensive than just using Aspen2 with exactly the same results. I wont change, it works well for me and all my saws can be left full or half full or whatever for a couple of years and still start without all the hassle pump petrol brings.
Have fun, dont get frustrated, life is too short.

 

[bwalker]

Less oil equals less heat. I've tried 25:1 and 50:1. It's a noticeable jump in cyl heat. Might even try Amsoil's 80:1 someday.

Great, runs cooler cylinder head temps up until you lunch a bearing.

 

[bwalker]

My buddy ran ATF in his Hoodaka Combat Wombat. Never seized.

You are dating your self there.

 

[lone wolf]

You are dating your self there.

I suppose but that wasn't the point. You too if you know what the hell a Wombat is.

 

[NSEric]

I have a back ground in two stroke dirt bikes.
32-1 makes the crank bearings last longer than 50-1 does, thats the biggest difference between the two mixtures, the motors run the same and the pistons last fine either way but the bearings like the extra lube.

 

[bwalker]

I have a back ground in two stroke dirt bikes.
32-1 makes the crank bearings last longer than 50-1 does, thats the biggest difference between the two mixtures, the motors run the same and the pistons last fine either way but the bearings like the extra lube.

On strato charged engines I will not run a drop less oil than 32:1.
IME running more oil provides for longer lasting and internally cleaner engines.

 

[Smitty Smithsonite]

I have a back ground in two stroke dirt bikes.
32-1 makes the crank bearings last longer than 50-1 does, thats the biggest difference between the two mixtures, the motors run the same and the pistons last fine either way but the bearings like the extra lube.

I do too, but I'll say that's not really true. It is VERY dependent upon oil quality. Far too many variables to pin it on ratio alone. Even just between synthetics alone there's a wide quality range, let alone between a regular dino oil and a synthetic.

I've run Amsoil Saber at 100:1 in all my hand held 2-stroke equipment for all of 15 years now - I have yet to have a lubrication-related failure. In fact, since I've switched to this oil I've had less mechanical wear in general. Plus no more scraping exhaust ports and piston crowns of huge amounts of carbon. Added bonus, it's a fuel stabilizer too. I didn't believe any of the claims until I saw and experienced it for myself.

 

[bwalker]

I do too, but I'll say that's not really true. It is VERY dependent upon oil quality. Far too many variables to pin it on ratio alone. Even just between synthetics alone there's a wide quality range, let alone between a regular dino oil and a synthetic.

I've run Amsoil Saber at 100:1 in all my hand held 2-stroke equipment for all of 15 years now - I have yet to have a lubrication-related failure. In fact, since I've switched to this oil I've had less mechanical wear in general. Plus no more scraping exhaust ports and piston crowns of huge amounts of carbon. Added bonus, it's a fuel stabilizer too. I didn't believe any of the claims until I saw and experienced it for myself.

Just because your equipment hasn't blown up is pretty low bar.

 

[Smitty Smithsonite]

I work on at least 20 customer's saws, and theirs haven't blown up either, so ....

Neighbor cut 10 acres of MA trees with one Stihl saw running 100:1. His prior saws running cheap oil were all over here with worn rings, excessive carbon buildup, and worn crank bearings with leaky seals after half that.

 

[rogue60]

I do too, but I'll say that's not really true. It is VERY dependent upon oil quality. Far too many variables to pin it on ratio alone. Even just between synthetics alone there's a wide quality range, let alone between a regular dino oil and a synthetic.

I've run Amsoil Saber at 100:1 in all my hand held 2-stroke equipment for all of 15 years now - I have yet to have a lubrication-related failure. In fact, since I've switched to this oil I've had less mechanical wear in general. Plus no more scraping exhaust ports and piston crowns of huge amounts of carbon. Added bonus, it's a fuel stabilizer too. I didn't believe any of the claims until I saw and experienced it for myself.

As stated just because something hasn't blown up isn't really a good indicator of how an oil is performing.
Rings need oil to seal. It has been proven over and over on dynos and the like the more oil the better the ring seal in a 2T the results of this being more hp.
I'd imagine 100:1 offers poor ring seal I bet blow by would be high.
I'd like to see pics of a piston/rings out of a saw run on 100:1 bet it's nice and black below the rings from blow by.

 

[Dennbb]

I'm looking for real-life empirical data showing the relationship between oil mix ratios and cylinder head temperatures. We've all heard statements like: more oil in the mix means less fuel -- so the air/fuel mixture is leaner and that makes more heat". Or: "I run 32:1 oil to provide more lubricity and I've never had a saw fail due to a lean mixture condition". I would like to see a real-world scientific evaluation that documents the cylinder head temperature change when running 50:1 vs. 40:1 vs 32:1. Same saw. Same base fuel. Same oil. Same ambient temperature. There seems to be a lot of strong opinions on this matter, but I wonder how much of the various opinions are anecdotal, hearsay, or culturally motivated. Myth or Fact? This might be a good test for Project Farm on YouTube.

JQ

Opinions on any subject are anecdotal, hearsay, or culturally motivated. There isn't any real research. Likely because manufacturers and researchers don't consider it an issue. Whereas too little oil is an issue to them. Personally I think it's a ludicrous assumption that 32:1 will cause more heat. There's the assumption that oil burns hotter than gas. It doesn't. The auto ignition temperature of synthetic oil is 590 - 680°f. Crude oil is 400-500° Gasoline is 685° f. Oil and gas are both 86% carbon. The difference between 32:1 and 50:1 is about 1.3 oz per gallon. A midsized saw would be about 6 tank's per gallon. 32:1 is about 1/5 of an ounce more per tank. About 1/2 teaspoon. And since oil ignites at a lower temperature there is no way it could cause a lean condition. Myth.

 

[Smitty Smithsonite]

As stated just because something hasn't blown up isn't really a good indicator of how an oil is performing.
Rings need oil to seal. It has been proven over and over on dynos and the like the more oil the better the ring seal in a 2T the results of this being more hp.
I'd imagine 100:1 offers poor ring seal I bet blow by would be high.
I'd like to see pics of a piston/rings out of a saw run on 100:1 bet it's nice and black below the rings from blow by.

Saber is one of the highest viscosity 2-stroke oils I have ever seen. Nothing comes remotely close to it. There is zero blow by in any engine that has run it since after it was broken in. I don't have any pics because I've never torn down any engine my customers run the stuff in. Compression is high.

I do have pics of cheap oils results, though - the rings on this one took a blowtorch to remove. Both sides of the piston were BLACK. Blackest I've ever seen. This owner had a penchant for running the cheapest crap oil he could find:

 

[Smitty Smithsonite]

Opinions on any subject are anecdotal, hearsay, or culturally motivated. There isn't any real research. Likely because manufacturers and researchers don't consider it an issue. Whereas too little oil is an issue to them. Personally I think it's a ludicrous assumption that 32:1 will cause more heat. There's the assumption that oil burns hotter than gas. It doesn't. The auto ignition temperature of synthetic oil is 590 - 680°f. Crude oil is 400-500° Gasoline is 685° f. Oil and gas are both 86% carbon. The difference between 32:1 and 50:1 is about 1.3 oz per gallon. A midsized saw would be about 6 tank's per gallon. 32:1 is about 1/5 of an ounce more per tank. About 1/2 teaspoon. And since oil ignites at a lower temperature there is no way it could cause a lean condition. Myth.

Not a myth - you're not understanding the reason for the lean-ness. It's not due to ignition - it's due to the fact that oil displaces fuel. When you add oil to gasoline, you are adding oil molecules to where fuel molecules once were. More oil, less fuel in the mix. Less fuel is lean, no matter how it's done.

 

[bwalker]

Not a myth - you're not understanding the reason for the lean-ness. It's not due to ignition - it's due to the fact that oil displaces fuel. When you add oil to gasoline, you are adding oil molecules to where fuel molecules once were. More oil, less fuel in the mix. Less fuel is lean, no matter how it's done.

But what your not considering is the change in 20 degrees of ambient temp has a much greater effect than a bit more oil in the fuel.
Most guys can't tune a carb to save their lives and are way rich anyway.
With the newer gen says with compensating carbs or FI your tuning is bang on all the time regardless of ratio.

 

[oldbuzzard]

Hodaka Combat Wombat! That's a name I've not heard in a long time...Back in the day, my buddy owned a 1973 Combat Wombat. I think it was 125cc. Dang. Memory lane...

JQ

OMG— me and my brothers all raced motorcycles back in the day, enduros and hare scrambles. Those Hodakas had a distinctive sound out in the woods, like swarms of angry bees coming down the trail.