OilHead
ArboristSite Guru
He wanted to know about head temps so there it is. Oh & sence there are no published factory specifications on pop how exactually do you know its even close to being correct ?
why a muffler mod lowers internal engine temps
- Thread starter drmiller100
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Nitroman
Addicted to ArboristSite
So far no-one seems to have it pinned down why an easier breathing motor lowers operating temps.
timberwolf
Addicted to ArboristSite
I mess around a few yeas ago on this, maybe something here that can help you Scott.
http://www.arboristsite.com/showthread.php?t=6199&highlight=muffler+temperature
I would do things differently now if I did the same experiments. mixture and carb setting play a large role in head and exhaust temperatures. If you open up a muffler and don't reset the jetting internal engine temps may end up higher than stock due to an overly lean mixture. If you rejet to keep RPM down then the mixture maybe effectivel richer and bring down engine temps, but exhaust tems can be higher due to more unburnt fuel burning late close to the exhaust port openening period.
http://www.arboristsite.com/showthread.php?t=6199&highlight=muffler+temperature
I would do things differently now if I did the same experiments. mixture and carb setting play a large role in head and exhaust temperatures. If you open up a muffler and don't reset the jetting internal engine temps may end up higher than stock due to an overly lean mixture. If you rejet to keep RPM down then the mixture maybe effectivel richer and bring down engine temps, but exhaust tems can be higher due to more unburnt fuel burning late close to the exhaust port openening period.
Lakeside53
Stihl Wrenching
oh.. watchng a few zillion saws in operaton.. and a dozen or two of mine..
OilHead
ArboristSite Guru
Well that proves it & can finally put this thing to bed once & for all. I just was'nt buying the arguement that if we have two snakes one of them in an orange box & the other in a black box that we could never declair the one from the black box as being gospel because it had'nt been blessed prior to leaving its birth place. Ha Ha Ha looks like a few non beleivers have been bit.
:monkey: Interesting analogy. Anybody want to explain to me what it means?
Lakeside53
Stihl Wrenching
The timberwolf tests are really great, but there is little difference in "3 cut" cylinder head temperatures until the muffler is opened up to 6 times the factory size... I sure don't open mine close to that big...and won't.. and rarely see any that are, Part of it's job is to "muffle", and run well 
Back to a world without orange and black snakes... It's not really making much difference at all! Stock (0.11sq.in.) 105C, (0.30sq.in) 96C, (0.45sq.in) 105C ...
I like to do some tests at more than "3 cut" totaling 6-7 seconds ; like mill a section of wood for 2 minutes. i.e. full continous HP, not three short bursts.
Back to a world without orange and black snakes... It's not really making much difference at all! Stock (0.11sq.in.) 105C, (0.30sq.in) 96C, (0.45sq.in) 105C ...
I like to do some tests at more than "3 cut" totaling 6-7 seconds ; like mill a section of wood for 2 minutes. i.e. full continous HP, not three short bursts.
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drmiller100
ArboristSite Guru
i think your math is off. .1 atm is not 7 psi.
modern 2 strokes such as bikes and sleds normally run at 2 to 4 psi pressure in the pipe. but, they are modern.
i should probably throw a gauge on the cat muffler i have.
compressors get hot not from teh "friction", but rather from the fizzicks fact that when you compress air, it gets hotter.
when you let it "decompress", it cools off.
http://home.howstuffworks.com/refrigerator4.htm
ideal gas law is a little confusing for the fizzicks behind this. "combined gas law" is a better description.
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drmiller100
ArboristSite Guru
The timberwolf tests are really great, but there is little difference in "3 cut" cylinder head temperatures until the muffler is opened up to 6 times the factory size... I sure don't open mine close to that big... rarely see any that are, and won't. Part of it's job is to "muffle", and run well
Back to a world without orange and black snakes... It's not really making much difference at all! Stock (0.11sq.in.) 105C, (0.30sq.in) 96C, (0.45sq.in) 105C ...
I like to do some tests at more than "3 cut" totaling 6-7 seconds ; like mill a section of wood for 2 minutes. i.e. full continous HP, not three short bursts.
it appears to me that you are going to stick with your notion that opening a muffler makes them run hotter, not colder, despite empirical evidence to the contrary.
that is your choice.
OilHead
ArboristSite Guru
Quiet mufflers we dont need no stinkin quiet mufflers. Take a close look at some of the older Macs & you'll soon discover that the relation between total size of the exit area vrs the port itself is more than doubble . Also the pop pressures were around 15 psi vrs. 20+ . To me this explains why there are still a lot of older saws still running to this day & it is because they were'nt all stomped down & run cooler. I've seen to many dead ones at my dealer for my liking ,where the exhaust side has gone thru a melt down & not because it had been straight gased. For 99% of the homeowner types that just want a saw in case of a blow down in the driveway its probably overkill & the time & money involved isnt worth messin with. But for those of us that are power hungry its the only way to go.
slabmaster
ArboristSite Guru
I feel that the modern ethonal gas has alot to do with the burned up saws.It creates a leaner mixture which can cause meltdown from extra heat.THe carb would have to be richened to comensate and your fuel useage will go up.Yet they still push in on us.Seems someone wants us to spend more on fuel and saws.:censored:
chowdozer
Addicted to ArboristSite
That was already addressed.
okay, I goofed. I'll use your excuse. Too much beer!
Your initial post and the title of the thread is about mufflers.
I never studied "fizzicks", but I did study physics. Chemistry too.
So, two different animals. compressors don't have a fire in them and we're not concerned about the dynamics of flow on the exhaust of a compressor. I have yet to see a saw blowing 175 psi out the exhaust.
If you haven't measured the pressure on a stock and modified muffler and know the difference in pressure, how can you attribute the muffler to the saw running cooler?
How do you measure muffler and piston temps and how do you approach repeatability?
Do you use a dyno and an exhaust gas analyzer?
Basically, from you I get:
The claim a saw runs cooler if you open up the muffler.
You believe the pressure drop from opening a muffler causes it to run cooler, yet you ignore the increase in fuel when you retuned it. If you believe you saw a reduction in temp, what caused it? The muffler or the increased fuel?
You won't say how you measure muffler or piston temps.
You won't address repeatability.
Do I have that right?
Years ago, before computers made it into cars, we used to run a couple of hairdryers on a sbc 350 with draw through Holley 650's. Along about 800 horses or so you run into serious detonation problems. Water injection to the rescue.
The point I wish to make from above, study up on latent heat, ie: the absorption or emission of heat when a substance experiences a phase change. Basically evaporative cooling in the case we are discussing. The same gasoline that feels cold on your hand feels cold when it enters the combustion chamber. It has alot more effect than the miniscule differential pressure you're going to see with a muffler mod.
Timberwolf hit the nail on the head several posts ago when he wrote about the variables involved which is why I ask if you are using a dyno and EGA and how you are addressing repeatability.
slabmaster
ArboristSite Guru
All i can say is that the more heat retained in the muffler,the hotter the cylinder will get,as the heated up muffler is bolted to it.The larger the exit hole is on the muffler the cooler it will stay,as those hot gasses will be able to exit more completely to keep the engine cooler.And yes,more air&fuel can aid in cooling as well.That's my thoughts on the subject.
Lakeside53
Stihl Wrenching
I'm not seeing any material evidence to support your theory either
.. even the 6x factory opening temp drop could have been due to the enrichment TW did. Maybe? The 3x/4x opening don't show any material changes.It's a complex topic with no black and white answers... my contention is that increased HP increases heat, but it's not a "switch".. and depends on many variables. Whether the increased heat is removed faster then it is generated depends on a whole slew of variables.. And one test (thank god.. uh, TW.. we have at least one) cannot necessarily be extrapolated across all saws; some may be a lot worse, or even better...
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huskydave
Addicted to ArboristSite
From all the research I have done. It seems that every saw is different and no one conclusion can be made because tolerances vary and porting mufflers will increase power but is not the same as designing a pipe for a given engine. If you can get lower temps from a muffler modded saw than fine but if the saw is running 2000rpms faster than a LOT more heat is being produced so I would think thermal dynamics would play a part and the quality ie Grain structure of the steel would even play a part along with may other variables. I don't like the experiments that show (1) saw did this and now that is the best approach because clearly it isn't. If the result's rang true on 100 saws rather than five we have a good base for a discussion but a lot of it is blowing smoke imo. Their are some ways to get gains from every saw out there but when you start comparing numbers and give the answer this is what to do for said saw think about all the variables involved: fuel type, condition of saw, builders experience, squish numbers, casting flaws, hours on saw, carb type, carb settings etc... I can say this, just doing a mufflermod may decrease the exhaust temperature on one saw but on another saw in another case it may not. The only way to say conclusively would be for a builder to mod only one model of saw and perfect the numbers to a point that everyone that ran his saws was satisfied and won races or never complained about the gains made. the other point Lakeside was making is that a racesaw is another animal meaning it is meant to compete for a few seconds and shut down and a regular worksaw will need to keep torque and reliability and last a while before blowing up. If we can get some more honest answers from the good saw builders Im not talking about timberwolf Romeo or Denis cahoon and just learn and adapt we will all benifit from thier knowledge and can build some on the edge worksaws instead of buying an expensive saw that weighs more. I love reading posts from those guys and I would have built a few rasesaws by now if it was easier to gain knowledge but I did learn what I needed to win and even came up with a few unique ideas even if they were unpractical but then most of the top guys won't share what they know and put me down before I even had the chance to compete. That makes me think they are a little too paranoid.
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Nitroman
Addicted to ArboristSite
It would be nice to read some posts from those who have engineering backgrounds, but I believe they don't post because they don't want to get ripped by people who have no understanding of what they are doing.
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drmiller100
ArboristSite Guru
many have been banned for one reason or another.
in any case, lets try this another way.
if you guys really believe that openeing the muffler up makes them run hotter, then do you believe that if we were to close the muffler outlet down in size, it would then run cooler???
gtstang462002
ArboristSite Operative
All i can say is that the more heat retained in the muffler,the hotter the cylinder will get,as the heated up muffler is bolted to it.The larger the exit hole is on the muffler the cooler it will stay,as those hot gasses will be able to exit more completely to keep the engine cooler.And yes,more air&fuel can aid in cooling as well.That's my thoughts on the subject.
Adding air and fuel is going to make a hotter fire....
gtstang462002
ArboristSite Operative
I believe that your combustion temps at the time of combustion are not going to change much if any. Though general rule of thumb is more BTU=More HP
timberwolf
Addicted to ArboristSite
Huskydave, you raise some good points, but we got to keep engine mods out of the equation or all bets are off on engine and exhaust temps.
Just talking a muffler mod on a stock engine, if you get into porting there are likely over a hundred variables that will affect the results.
Yes the saw is turning faster, and producing more power, but also the fan is being spun faster and the cooling system in overdrive. Other things too, opened up mufflers = richer jet settings and more unburn fuel, don't think there is much dispute on that point. So with more fuel being pumped in there is extra cooling source being provided. I think you are correct in saying more total heat is being produced if more power is made, but where that heat ends up is another question. With higher RPM combustion is going to move later in the power stroke, might even be possible to see heat leave the head and show up more in the exhaust and possibly exhaust side of the piston crown.
Other factors too, richer mixtures produce lower flame temps, so on many saws if the muffler is opened up and maximum factory reccomended RPM is to be respected the mixture will effectivly need to be richer. Resulting in lowered flame temperatures.
In other cases where the saws turn faster to make the extra power found in a muffler mod, peek cylinder pressures and torque can acctually drop at the cutting RPM yet more HP can be present due to the RPM factor. When cylinder peek preasures drop temperatures in general do too.
Something else I find interesting is how engine and exhaust temperatures can go in different directions. Some changes in engine design can move heat from the head to the exhaust or just as easy the other way around. It is likely a misconception to think that hotter exhaust temps = hotter engine temps, though radiative and conductive heat from muffler to the jug are certainly a factor.
The exhaust side of a air cooled jug can be easily 50 deg C hotter than the intake side, making for some interesting thermal expansion issues. No one thinks much of it in design of simple consumer two strokes, but high end race engines have taken stuff like this into account in precision machiening components to fit best at opperating temps.
Just talking a muffler mod on a stock engine, if you get into porting there are likely over a hundred variables that will affect the results.
Yes the saw is turning faster, and producing more power, but also the fan is being spun faster and the cooling system in overdrive. Other things too, opened up mufflers = richer jet settings and more unburn fuel, don't think there is much dispute on that point. So with more fuel being pumped in there is extra cooling source being provided. I think you are correct in saying more total heat is being produced if more power is made, but where that heat ends up is another question. With higher RPM combustion is going to move later in the power stroke, might even be possible to see heat leave the head and show up more in the exhaust and possibly exhaust side of the piston crown.
Other factors too, richer mixtures produce lower flame temps, so on many saws if the muffler is opened up and maximum factory reccomended RPM is to be respected the mixture will effectivly need to be richer. Resulting in lowered flame temperatures.
In other cases where the saws turn faster to make the extra power found in a muffler mod, peek cylinder pressures and torque can acctually drop at the cutting RPM yet more HP can be present due to the RPM factor. When cylinder peek preasures drop temperatures in general do too.
Something else I find interesting is how engine and exhaust temperatures can go in different directions. Some changes in engine design can move heat from the head to the exhaust or just as easy the other way around. It is likely a misconception to think that hotter exhaust temps = hotter engine temps, though radiative and conductive heat from muffler to the jug are certainly a factor.
The exhaust side of a air cooled jug can be easily 50 deg C hotter than the intake side, making for some interesting thermal expansion issues. No one thinks much of it in design of simple consumer two strokes, but high end race engines have taken stuff like this into account in precision machiening components to fit best at opperating temps.
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