Engine cooling

[Keith Gandy]

I'm wondering if the heat can vaporize the fuel at the transfers causing the charge to lose some velocity? I'm also wondering if it renders the sound waves ineffective.

!! Jim u r over my head man but u and drf should have some very interesting talks !! U two seem to have her nailed down in theory

 

[Keith Gandy]

I'm wondering if the heat can vaporize the fuel at the transfers causing the charge to lose some velocity? I'm also wondering if it renders the sound waves ineffective.

Ive been wondering more lately on velocity through the transfer loop vs the exhaust volume and tuning in the exhaust area. In my mind Im thinkin thats where alota in cut rpm can be made

 

[David Young]

I'm wondering if the heat can vaporize the fuel at the transfers causing the charge to lose some velocity? I'm also wondering if it renders the sound waves ineffective.

I think charge density and cylinder filling would be more at play. I'm sure someone has an answer.

 

[drf256]

I think charge density and cylinder filling would be more at play. I'm sure someone has an answer.

I think so too.

 

[Keith Gandy]

I think so too.

Would yall please explain

 

[mdavlee]

You get too much heat and the gas can't cool. Cooler fuel and charge is more dense and makes more power. Best guess I can come up with. The oil is supposed to come out of the charge in the case as the gas changes from liquid to gas to flow through transfers.

 

[angelo c]

I think charge density and cylinder filling would be more at play. I'm sure someone has an answer.

I think timing has an equally important effect as well. Cyl heats vary greatly with spark fire timing and efficiency as well.
Stoichiometric mixtures as well.

Back in muh airplane days the arguments were if we could efficiently run at peak or leak of peak for cooler cylinder temps. air-cooled 4 stroke engines...Terry if you ever want to study airflow importance in cyl cooling...look under the cowl of an air-cooled airplane...man that gets complicated.

 

[Keith Gandy]

You get too much heat and the gas can't cool. Cooler fuel and charge is more dense and makes more power. Best guess I can come up with. The oil is supposed to come out of the charge in the case as the gas changes from liquid to gas to flow through transfers.

Ok thanks Mike. Makes sense and would explain why the dirtbike racers chill that fuel

 

[Terry Syd]

I used to black anodize my cylinder and the shocks on my bikes. A black surface will radiate more heat than a white surface. In one of my physics classes in college the professor took a white ceramic crucible bowl, painted a black 'X' on the side, then stuck the flame of a Bunsen burner into the bowl. He had a student turn off the lights in the classroom. Within about a minute the 'X' began to glow red, then orange, then finally white - the black 'X' was radiating more heat than the rest of the bowl. It was one of those experiments that you had to see to believe it.

I've also tried ceramic coated pistons and black anodized pistons - the biggest factor I found in keeping an air-cooled engine cooler was MORE AIR ACROSS THE FINS. If the amount of air is limited, then I rework the fins to get the air into the fins. Little things, like rounding the leading edge of the fin so the turbulence of hitting a flat leading edge doesn't disrupt the flow.

I used to write tech articles for a bike magazine in Oz. One of the articles dealt with fin technology. You won't find much discussion about such an issue nowadays - all that science was worked out in the 1930s. The pictures I used in the article came out of those documents and made the article look like a historical piece rather than tech article for modern bikes.

 

[Terry Syd]

Back to what I originally proposed - is anyone interested in doing a test to try and quantify how much power is lost on a chainsaw by something like the air injection system. That is an easy test, just block off the system.

You can also rework the fins on other saws. On the Stihl 029-390 series there is a casting flange for the clutch side muffler bolt that blocks the air flow. In fact, it is worse than just blocking the flow. It expands as it gets hot and pushes inward on the cylinder. You get both a 'hot spot' and reduced clearance at the same spot. I have seen two 029 cylinders that both seized at that spot. Just open up the manufactured casting (drill and dremel) and the problem goes away.

 

[drf256]

In my head, Ideally, you want the densest charge possible in the combustion chamber with enough heat to just keep the fuel perfectly vaporized. Then you want enough compression to heat that mixture up to the point just near detonation. Then you want to fire it at the perfect time to create the greatest pressure to drive the piston down for max power.

Easily said, tough to accomplish.

 

[drf256]

I used to black anodize my cylinder and the shocks on my bikes. A black surface will radiate more heat than a white surface. In one of my physics classes in college the professor took a white ceramic crucible bowl, painted a black 'X' on the side, then stuck the flame of a Bunsen burner into the bowl. He had a student turn off the lights in the classroom. Within about a minute the 'X' began to glow red, then orange, then finally white - the black 'X' was radiating more heat than the rest of the bowl. It was one of those experiments that you had to see to believe it.

I've also tried ceramic coated pistons and black anodized pistons - the biggest factor I found in keeping an air-cooled engine cooler was MORE AIR ACROSS THE FINS. If the amount of air is limited, then I rework the fins to get the air into the fins. Little things, like rounding the leading edge of the fin so the turbulence of hitting a flat leading edge doesn't disrupt the flow.

I used to write tech articles for a bike magazine in Oz. One of the articles dealt with fin technology. You won't find much discussion about such an issue nowadays - all that science was worked out in the 1930s. The pictures I used in the article came out of those documents and made the article look like a historical piece rather than tech article for modern bikes.

I think its called "Emissivity" in technical terms. Spelling may be off.

 

[bikemike]

I've also blocked off the air injection for that reason. Just be careful where you add holes for intake or the filter will get clogged a lot quicker than expected.

My echo 360 t was horrible for that on the air injection. I drilled a few holes in the filter cover and it was night n day difference, plus my saw seems to breath better

 

[Lightning Performance]

Before you guys go off looking for 2% and 3% go take a serious look at your fuel map. Remember your dealing with a carb not injection here. The only way to "see" it is with an emissions tester, O2 sensor, the dyno readings and/or all three preferred. Go find and figure out how to cover up the flat spots. All this peak temps for power talk gets burnt down real quick in a flat spot. Detonation takes out pistons in under 2 seconds in some cases ie: high static compression ratios and advanced ignition spark. Air flow over the fins and cool fuel is where it's at. That all goes to hell on a hot day real quick.

If your going to play with lean and hot go rob a 480I or 500I to see what is possible before the burn-down.

 

[Terry Syd]

I guess the answer is 'no'. At least the topic provides more fodder for forum chatter.

 

[angelo c]

I guess the answer is 'no'. At least the topic provides more fodder for forum chatter.

Let me give it a try...

@Redbull661 ...we'll see if Julian is interested....

 

[Chainsaw Jim]

It seems like there could be a better shroud or air dam to direct the air flow from the flywheel to the hottest portion of the cylinder. The bases are always caked with crap and the tops are generally clean.

 

[Redbull661]

All I can tell you is what I've noticed and what I've got in results.

Timing key test on 661 using .075, .065, .055, .050, .045, 0.035- The jug temp did not change at all. maximum rpm changed. Cut times changed. But jug temp did not. TM explained it and it went over my head.

I've noticed cut times are slower if the saw is too cold. Why I always do a "burn" cut. before the actual test cuts.

I've noticed that with thin weave screens in ported 661 muffler 2nd and 3rd cut times are slower than 1st cut.

I've noticed with wide weave screens in ported 661 muffler 1st 2nd and 3rd cuts are very consistent.

I've noticed with baffle in the ported 661 muffler that 1st cut time is fast and 2nd and 3rd cuts get slower

I've noticed with baffle out in the ported 661 muffler that 1st 2nd and 3rd cut times are very consistent.


You guys can debate why I got the above results. I'm staying out of it. Although I will say I think heat goes both ways...too little or too much. Why that is. I don't know enough to answer.

 

[Chainsaw Jim]

I was hoping the human variable would chime in. lol
I'm glad you were able to get those results established. I've been wondering if screens made any difference and you have answered my question on that.
Your results also point towards increasing flow to keep temps in better check.

 

[drf256]

All I can tell you is what I've noticed and what I've got in results.

Timing key test on 661 using .075, .065, .055, .050, .045, 0.035- The jug temp did not change at all. maximum rpm changed. Cut times changed. But jug temp did not. TM explained it and it went over my head.

I've noticed cut times are slower if the saw is too cold. Why I always do a "burn" cut. before the actual test cuts.

I've noticed that with thin weave screens in ported 661 muffler 2nd and 3rd cut times are slower than 1st cut.

I've noticed with wide weave screens in ported 661 muffler 1st 2nd and 3rd cuts are very consistent.

I've noticed with baffle in the ported 661 muffler that 1st cut time is fast and 2nd and 3rd cuts get slower

I've noticed with baffle out in the ported 661 muffler that 1st 2nd and 3rd cut times are very consistent.


You guys can debate why I got the above results. I'm staying out of it. Although I will say I think heat goes both ways...too little or too much. Why that is. I don't know enough to answer.

Ever retard the timing on a car with headers and check temps? They will glow red if you don't watch out.

Up to a point, advancing timing to optimal should cause more chamber retained heat and less out the exhaust. More power. More ability to cool cylinder with incoming charge. The exhaust port won't get cooled by burned gasses.