50:1 vs 40:1

[Terry Syd]

As far as getting more heat out of the cylinder, I eventually blocked off the 'air injection' system on both my Husky 450 and 365BB. The more I modded the saws, the more air was sucked into the engine and the less was available for cooling the fins. The power was going up at the same time the cooling air was going down.

I was getting very close to sticking the 450 before I figured out what was happening. I didn't notice any increase in power (that wasn't my focus at the time, but may have), but I did sigh with relief when I saw the plug was finally running at a decent temp.

 

[edisto]

As far as getting more heat out of the cylinder, I eventually blocked off the 'air injection' system on both my Husky 450 and 365BB. The more I modded the saws, the more air was sucked into the engine and the less was available for cooling the fins. The power was going up at the same time the cooling air was going down.

Now there is a tradeoff that would not have occurred to me!

Definitely a useful bit of info Terry!

 

[Andyshine77]

As far as getting more heat out of the cylinder, I eventually blocked off the 'air injection' system on both my Husky 450 and 365BB. The more I modded the saws, the more air was sucked into the engine and the less was available for cooling the fins. The power was going up at the same time the cooling air was going down.

I was getting very close to sticking the 450 before I figured out what was happening. I didn't notice any increase in power (that wasn't my focus at the time, but may have), but I did sigh with relief when I saw the plug was finally running at a decent temp.

That's not a bad idea, I've also seen holes in the filter covers, this would likely have a similar effect.

 

[husq2100]

...............Do a better job of cooling the cylinder, and you will increase heat transfer from the piston.

so for a Dumby like me what effect does Oil to fuel ratio have on this? Taking into account proper tuning for a specific ratio.

more oil = more heat, but is that because it is making more power. :msp_ohmy: bugger now Im confused again?

 

[Terry Syd]

With the air injection system blocked off, I had to make some holes in the back of the cover for the filter in order for the engine to breath. With the holes over the handle, there are less 'fines' sucked into the airbox. The air injection system will pull air in through the front of the starter cover that sucks the fines off of the bar and chain. The air injection system works well for the bigger stuff, but the fines get sucked through the air injection system into the filter area.

The Aussie hardwoods are notorious for creating fine sawdust. I noticed that the fines in the airbox dropped to about 20% of what they were before the air injection system was blocked off.

 

[Andyshine77]

so for a Dumby like me what effect does Oil to fuel ratio have on this? Taking into account proper tuning for a specific ratio.

more oil = more heat, but is that because it is making more power. :msp_ohmy: bugger now Im confused again?

More heat yes, but how much more heat? from my memory the difference in heat from 50:1 to 32:1 was nominal. Running more oil isn't simply about more lubrication. Yes ring seal is improved, but with the rpm's some saws run keeping the seals wet is a good thing. Oil can also act like a cushion, a plus when you raise compression.

In a normal work saw heat isn't normally a big problem, but keep in mind all air cooled engines have heat issues. Now I've seen and heard saws overheat, normally an over heating saw will race after making a cut, and they obviously lose power. These saws were not what I would call work saws IMHO.

 

[husq2100]

............... With the holes over the handle, there are less 'fines' sucked into the airbox........

Terry, Im having trouble visualizing where you drilled the new air holes ???

 

[Terry Syd]

I wish the new computer system upgrades would allow me to send pictures (don't you love updates you didn't ask for). - A picture would be worth a thousand words.

Anyway, on top of the saw, is the lid that goes over the air filter. I drilled holes in the back of that lid. The holes are located in front of my right hand and draw air from the back of the saw, away from the sawdust generated by the chain.

I suppose it is also a 'cold air intake' as there is no pre-heating done by the compression of the flywheel. Timberwolf indicated he found about a 10F rise in the temperature of the air off of the flywheel.

 

[husq2100]

Thanks Terry, I have seen holes in race saws where you mention. Now a slightly off topic but related question, does air flow better through round holes drilled in the plastic shroud or would it be better to cut a larger section out and fit a screen. I have heard that air flows better through a grill of twist wire than holes in perfferated sheet.....surface area would come into play, but lets say you are going to drill 3/8th holes leaving 1/4 between them, in a 2 sqaure inch area or just cut the whole 2 sqare inches out and fit a screen mesh of some sort. S/Steel secruity screen comes to mind....

 

[Terry Syd]

I just drilled big enough holes that I knew the engine could breath. The screen might help keep some of the chips out, but it is the dust that I worry about.

On the 450 I have the holes drilled low enough that the air entering the box impacts on a plastic side of the filter. I then wipe some grease on the plastic and it catches a lot of the dust that enters the air box.

 

[aussie2]

for the blokes in aus ,if u go down the street to your local husky or stihl dealership ask them what the number 1 cause of a chainsawsaw blowing up is" he will tell you its becouse people are running the 50:1 ratio that is in the manuals, i hounstly dont know anyone that usses this mixture here its well known not to. and from experience i blew up a mates 088 3 cuts threw a big messmate and shes seized like a ##### = tested his fuel and what did we find !!!!!!!!!!!

 

[aussie2]

for the blokes in aus ,if u go down the street to your local husky or stihl dealership ask them what the number 1 cause of a chainsawsaw blowing up is" he will tell you its becouse people are running the 50:1 ratio that is in the manuals, i hounstly dont know anyone that usses this mixture here its well known not to. and from experience i blew up a mates 088 3 cuts threw a big messmate and shes seized like a ##### = tested his fuel and what did we find !!!!!!!!!!!
the thread continues!!

 

[Terry Syd]

Come on Aussie 2, admit it, you're not really an Aussie, you're some Yank that is pretending to be an Australian.

 

[husq2100]

no disrespect but the few dealers I have chatted to, including Husky construction reps and Hire store mechanics dont really know the depth of what they talk about. I have heard that 50-1 will blow up saws and to run at 30 or 25-1, when I ask about re tuning to suit the new ratio they ask what am I talking about. Tell a concreter to run at 25-1 in his Construction saw and how the hell is he going to tune it when they are spline drive needles and the tools arent readily avialable here. Will he even know how to tune the saw?? I don't run my saws at 50-1, but that is not becuase I think my saw will blow up at that ratio.....and FWIW, I have had Stihl dealers tell me I absolutely have to run my Stihl string trimmer at 50-1 as the whole engine is designed to run at that AND the STihl oil is ONLY designed to run at 50-1. (I said Castrol make their oil and have no problems with different ratio's in other aplications, his response was it is formulated for Stihl and specific to 50-1....I got the feeling that if I changed the ratio the world would end)

I have also been told by a different dealer that I can not run Stihl chain on my husky as it is different, wont fit and wont work. Even when I said that if I had a 0.63 gauge bar (which is common Stihl gauge in 3/8) he said wont work......If you are running fresh non-ethonal fuel, good quality oil, clean filters, zero air leaks, sharp chain and correct tune I doubt running at 50-1 is going to kill a saw. JMO

 

[edisto]

so for a Dumby like me what effect does Oil to fuel ratio have on this? Taking into account proper tuning for a specific ratio.

more oil = more heat, but is that because it is making more power. :msp_ohmy: bugger now Im confused again?

TWs data are consistent with Bell's interpretation that more oil in the mix improves heat transfer from through the rings. That is why (with bean oil) he and Bell noted less gumming on the rings and less carbon deposition with more oil.

Using that interpretation, the reason the cylinder temperature went up, while the exhaust temp changed very little, was because more of the existing heat was being shed from the piston to the cylinder, as opposed to heating the charge in the crankcase. In the simplest sense, there was no additional being produced, the only thing that changed was the relative heat flux from the piston into its surroundings (the charge and the cylinder).

 

[one.man.band]

That's the Jenning's article I was referring too.

Bell found the same thing. His interpretation was not just about improved ring sealing, but improved heat transfer from the piston to the cylinder. More heat into the cylinder, less heat into the charge in the crankcase.

Less heat into the charge in the crankcase, less expansion of the charge, more charge for the same volume.

That is why I found TW's data so interesting. More heat transferred to the cylinder wall would explain the rise in cylinder temp, without a similar increase in exhaust temp.

"...improved heat transfer from the piston to the cylinder. More heat into the cylinder, less heat into the charge in the crankcase."

what??????? could you explain this further?
A. unless something has changed about two stroke motors.....the swept cylinder volume is part of the crankcase volume.
B. "heat transfer from piston to cylinder" ?????? actually......80% of heat in the top of piston is conducted through the ring. (the rest is transferred by a combination of the following: the piston skirt to cylinder wall, while also being cooled from the underside of piston by incoming air/fuel charge and of course cylinder fins). the skirts heat up mainly from the exhaust port. which is why most piston problems start in that area.

above: Jennings page 43; race engine technology: The Lord of Rings « RET-Monitor

as SLAMM correctly said. "You don't want the piston hot, there is no benefit to that beyond a normal amount of heat for expanding to proper running size and sealing." +1 sam

the idea is to keep heat out of the crankcase to get the coolest charge density just as you had mentioned. +1 edisto.

..................................................................
more rpm and more load is said require more oil.

maxima links i posted before; Bell page 167-169; and from yamaha engineers page 7 & 8 below

----------------------------------------------------
bells view of coatings: on intake/exhaust ports found here:

page 171-172

----------------------------------------------------
as long as motor is tuned for more oil, what is the aus guy's harm in running it? not a big deal at all.

 

[edisto]

"...improved heat transfer from the piston to the cylinder. More heat into the cylinder, less heat into the charge in the crankcase."

what??????? could you explain this further?
A. unless something has changed about two stroke motors.....the swept cylinder volume is part of the crankcase volume.

Jesus H. Tapdancing Christ.

Why is there always a direct correlation between the stupidity of the question, and the degree of snottiness with which it is asked?

The top of the piston is what gets hot. It is a short path, with a lot of area, to the bottom of the crown. The bottom is directly in contact with the charge. For that heat to heat the charge from the cylinder or the crankcase it has to travel out of the piston and into the cylinder...a longer path with much less area. The shortest route for heat to travel is through the piston to the nice, cool charge.

B. "heat transfer from piston to cylinder" ?????? actually......80% of heat in the top of piston is conducted through the ring. (the rest is transferred by a combination of the following: the piston skirt to cylinder wall, while also being cooled from the underside of piston by incoming air/fuel charge and of course cylinder fins). the skirts heat up mainly from the exhaust port. which is why most piston problems start in that area.

No ####.

I apologize for skipping over the obvious. I also forgot to mention that the most of the heat is generated by combustion, and that the fuel for combustion starts in the gas tank...should I go on?

There is no such thing as "80%" of the heat in any engine. It is 80% +/- X. What we are talking about here is the "X".

There are a lot of variables that determine X. The first is the actual amount of heat being produced, which varies even from cycle to cycle. Another is the rate at which heat is conducted out of the piston at its various points of loss. As I mentioned, the shortest path is to the charge. If transfer through the rings can be improved, then less heat will be transferred to the charge.

Now, in your mind, the surface of the rings and the cylinder might be flat, but in reality, they are not. The surface of the cylinder is rough...imagine waves on the ocean. The rings only contact the tops of the waves. Before coated cylinders, the cylinder surface was honed to produce grooves, and an important component of break in was to wear the peaks off of the waves to increase surface area for seal and heat transfer.

So...imagine the ring riding the top of the waves. Not much surface area for transfer. Fill the troughs of the waves with oil, and surface area available for transfer and sealing goes up.

More heat out through the rings is less heat that goes into the charge.

Yes...the cylinder contacts the charge too, but the cylinder also has a mechanism for transferring heat to the outside of the engine. I'd much rather have heat in the cylinder than in the piston.

 

[one.man.band]

clarity...not feather ruffling is all. misunderstood. i am a much better person knowing now, and all the facts i presented are deemed meaningless. apologize for making everyone dumber on this topic.

 

[3000 FPS]

Jesus H. Tapdancing Christ.

Why is there always a direct correlation between the stupidity of the question, and the degree of snottiness with which it is asked?

The top of the piston is what gets hot. It is a short path, with a lot of area, to the bottom of the crown. The bottom is directly in contact with the charge. For that heat to heat the charge from the cylinder or the crankcase it has to travel out of the piston and into the cylinder...a longer path with much less area. The shortest route for heat to travel is through the piston to the nice, cool charge.



No ####.

I apologize for skipping over the obvious. I also forgot to mention that the most of the heat is generated by combustion, and that the fuel for combustion starts in the gas tank...should I go on?

There is no such thing as "80%" of the heat in any engine. It is 80% +/- X. What we are talking about here is the "X".

There are a lot of variables that determine X. The first is the actual amount of heat being produced, which varies even from cycle to cycle. Another is the rate at which heat is conducted out of the piston at its various points of loss. As I mentioned, the shortest path is to the charge. If transfer through the rings can be improved, then less heat will be transferred to the charge.

Now, in your mind, the surface of the rings and the cylinder might be flat, but in reality, they are not. The surface of the cylinder is rough...imagine waves on the ocean. The rings only contact the tops of the waves. Before coated cylinders, the cylinder surface was honed to produce grooves, and an important component of break in was to wear the peaks off of the waves to increase surface area for seal and heat transfer.

So...imagine the ring riding the top of the waves. Not much surface area for transfer. Fill the troughs of the waves with oil, and surface area available for transfer and sealing goes up.

More heat out through the rings is less heat that goes into the charge.

Yes...the cylinder contacts the charge too, but the cylinder also has a mechanism for transferring heat to the outside of the engine. I'd much rather have heat in the cylinder than in the piston.

At last something that makes sense.

 

[Gologit]

Why is there always a direct correlation between the stupidity of the question, and the degree of snottiness with which it is asked?

Okay if I steal that line for a signature?

And just to drag us all, kicking and screaming, back to the original topic...are we using 40:1 or 50:1...just thought I'd ask. Politely.