Chris-PA
Where the Wild Things Are
Work is energy.
Power is the rate of doing work.
Torque is just a force and does no work at all.
Changing the weigh of the flywheel?
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Power is the rate of doing work.
Torque is just a force and does no work at all.
PartnerR16
ArboristSite Lurker
It’s this twisting motion that gets the chain in motion,so theoretically torque gets the initial work started before torque peak to allow Hp to maintain chain momentum at max RPM,IMO
Mastermind
Work Saw Specialist
I'm disengaging......
Chris-PA
Where the Wild Things Are
It's all just about power, and when people say "torque" they usually mean power at a low rpm - or often a broad flat horsepower curve with a lower peak rpm. Power makes things move.
Torque, power and work are words that are already defined, and using them to mean different things just leads to confusion.
A broad hp curve that peaks at a lower rpm is more useful for a work saw.
I need to digest all that new knowledge.
So Lets talk about longevity.
I think heavier flyweel give more stability to the engine and it last longer, it is improtrant in 4t especially under heavy load. But will it prelong 2t life?
Or am I mistaken?
So Lets talk about longevity.
I think heavier flyweel give more stability to the engine and it last longer, it is improtrant in 4t especially under heavy load. But will it prelong 2t life?
Or am I mistaken?
Rx7man
Cattle Rubbing Post
Chris, exactly! a 3 hp engine at 10,000 RPM does exactly the same amount of work in a given time as a 3hp engine that turns at 100 RPM.. the faster engine may need to be geared down to move a big load, but the slower one may need to be geared up to do a light load in a reasonable time
Trx250r180
Saw polisher
Ferguson system
Iggesund Forest dealer
I have a 2 cyl Lister engine mounted on a woodchipper. It has a huge flywheel and a long stroke. 2.1 Litre, 21 hp and 700 nm of torq (the same as a 7.3 powerstroke). The flywheel makes all the difference. I haven't been able to get it to stall yet, it will chug along so slow that you can hear each piston firing, but you can't kill it.
Rx7man
Cattle Rubbing Post
You aren't setting the bar very high comparing it to a powerstroke 
Our baler has a 400 lb 24" diameter flywheel... it can go through several strokes at full feed rate before the governor even kicks in on the engine... Flywheels are important for things have uneven or sudden loads.. balers, chippers, and even generators (when starting heavy loads).. On things that need to be responsive, they work against you.. sportscars, limbing saws, etc, but they still need to have some flywheel to not chatter like heck at lower RPM
Our baler has a 400 lb 24" diameter flywheel... it can go through several strokes at full feed rate before the governor even kicks in on the engine... Flywheels are important for things have uneven or sudden loads.. balers, chippers, and even generators (when starting heavy loads).. On things that need to be responsive, they work against you.. sportscars, limbing saws, etc, but they still need to have some flywheel to not chatter like heck at lower RPM
big t double
Addicted to ArboristSite
Why do you want a flywheel with no cooling fins? Just curious.
Philip Wheelock
Finis Origine Pendet
If you want a mid-size saw with rapid acceleration, get a Stihl 044 or ms440, but prepared for a loping idle. One strong word of advice, though: Don't mess with the flywheel on a work saw.
Rx7man
Cattle Rubbing Post
OK... I know those are slow turning engines, but the math doesn't quite work for me... 700nm of torque is 516 ft lbs, and for 21 hp it would have to do it at 216 RPM... I just really don't think any 2 liter engine can develop that kind of torque without forced induction... a Cummins 5.9 will get there (in relation to displacement) and requires 20 PSI of boost to do it.. the cylinder pressures are getting pretty darned high by then, so I think some numbers are out of whack somewhere
Here's the BMEP calculations
2 liter is about 120 cu in, and for 516 ft lb of torque, that's a BMEP of 650 PSI or 44 Bar.. which is rather unobtainable
Here's the link
http://www.epi-eng.com/piston_engine_technology/bmep_performance_yardstick.htm
And a quote from it about 'reasonable' BMEP
For a long-life (in an aircraft frame of reference), naturally-aspirated, SI (spark ignition) gasoline-fueled, two-valve-per-cylinder, pushrod engine, a BMEP over 204 PSI (14 bar, torque ratio of 1.35) is quite difficult to achieve and requires a serious development program and very specialized components.
It is worthwhile to note that a contemporary, normally-aspirated CI (compression-ignition) engine can easily make 15 bar of BMEP, and several turbocharged CI street engines routinely exceed 20.5 bar. It is helpful to remember that BMEP is a useful tool for comparing and evaluating similar types of engines.
Idahonative
Addicted to ArboristSite
Chris has a way of making people do that.
Idahonative
Addicted to ArboristSite
David Young
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why remove fins?
parasitic loss like underdrive pulleys on a street car.
you can also delete the clutch on a racesaw, less slip less weight.
it all about putting power to the chain.
on a limbing saw a heavier flywheel can help because you are at high rpm and may have 50 instantaneous shock loads on one tree. if the flywheel doesn't counter act that what will take the hit?
also on a saw they built them light because people like niko will say it is a pig if it weighs 6 oz heavier than the other manufacturer. I am sure it is a compromise.
does anyone remember the science experiment where you try changing the axis of a bicycle tire and then try it again when the wheel is spinning?
that force is the same on a chainsaw and one of the things that affect handling.
also if a modded saw is turning 1000 rpm more that is a lot more air probably more air than needed for cooling the saw that you opened the muffler optimized squish and timing on all of which can help with operating tempatures.
great thread
thank you
Cheers
parasitic loss like underdrive pulleys on a street car.
you can also delete the clutch on a racesaw, less slip less weight.
it all about putting power to the chain.
on a limbing saw a heavier flywheel can help because you are at high rpm and may have 50 instantaneous shock loads on one tree. if the flywheel doesn't counter act that what will take the hit?
also on a saw they built them light because people like niko will say it is a pig if it weighs 6 oz heavier than the other manufacturer. I am sure it is a compromise.
does anyone remember the science experiment where you try changing the axis of a bicycle tire and then try it again when the wheel is spinning?
that force is the same on a chainsaw and one of the things that affect handling.
also if a modded saw is turning 1000 rpm more that is a lot more air probably more air than needed for cooling the saw that you opened the muffler optimized squish and timing on all of which can help with operating tempatures.
great thread
thank you
Cheers
I think it's about time we discussed whether you need to run a different oil ratio if you alter the weight of the flywheel
Chris-PA
Where the Wild Things Are
Yet another interesting and worthwhile contribution to the topic.
Idahonative
Addicted to ArboristSite
In all seriousness, I've thought about this very subject many times. Everyone seems to agree for the most part that Echo's are torquey but it's always followed with the fact that they are heavier than the competition. My question is: Do Echo flywheels tend to be heavier than comparable models from other manufacturers?
Not sure, even if the flywheels were heavier, if it would make a significant difference in the overall weight of the saw.
That remind's me of something.
When you lighten flywheel in a street car you can bur your tires every time you start movig. But when you pass about 8k-9k rev its hitting a wall - doesn't want to go faster. In honda civic its around 140kmh-90mph.
light flywheel gives boost in low rpm.
Wouldnt be reasonable to make heavier flywheel for 70-80> cc saw? To get more torque in the cut.
When you lighten flywheel in a street car you can bur your tires every time you start movig. But when you pass about 8k-9k rev its hitting a wall - doesn't want to go faster. In honda civic its around 140kmh-90mph.
light flywheel gives boost in low rpm.
Wouldnt be reasonable to make heavier flywheel for 70-80> cc saw? To get more torque in the cut.
