Rpm, Torque, Displacement ???

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Okay Tzed, I concede that you are technically correct but I am using common parlance. In that usage torquey saws have the ability to keep the chain moving under heavy load/in big cuts where a fast revving and cutting saw might bog down and stop cutting altogether. A screamer may fly through 10 inch wood much faster than a slower design but be difficult to use on a 30"stump cut where the slower saw keeps on cutting about as fast as it does in 10" stuff. Those of us who have run a lot of saws have observed this first hand. Personally, I haven't really compared saws of the precise same displacement just noted that some relatively slow designs don't seem relatively slow when the bars are buried. I'm trying to understand enough to know what to expect from a given saw without actually doing side by side tests.

As far as flyheel weight is concerned-compare the seemingly unstoppable ability of an old one lung diesel with a 200lb flywheel turning at 500 rpm compared to some little engine that supposedly produces the same horsepower at 3000rpm. The difference is dramatic. Smaller faster spinning engines are definitely more effecient but they bog out a LOT easier. Compare Chippers with identical engines but different size/weights of cutter wheels. Big flywheels make performance differences-responses are slower both in getting up to speed and coming back down.

Thanks everyone-keep it coming! If I'm full of beans okay-just make me understand.:cool:
 
Rich, Husky, Stihl, Dolmar and perhaps others are using Nikasil. A nickel, silicon, tungsten matrix coating. It is both extremely hard and high in natural lubricity. (Techno -speak for " dang,it's slicky"). Properly applied hard chrome works extremely well-as attested to by all the old saws that have run hours upon hours and lasted through 3 sets of rings. :cool:
 
Originally posted by Stumper
Rich, Husky, Stihl, Dolmar and perhaps others are using Nikasil. A nickel, silicon, tungsten matrix coating. It is both extremely hard and high in natural lubricity. (Techno -speak for " dang,it's slicky"). Properly applied hard chrome works extremely well-as attested to by all the old saws that have run hours upon hours and lasted through 3 sets of rings. :cool:



Thanks Stumper.
 
Threoretically, the saw with the most horsepower should cut the fastest, as horsepower is rate at which work is done, however, the torque available at that maximum horsepower has to be equal to the torque required to turn the chain and make chips. If the torque required is less than that available, the rpm's will climb until the torque drops to an equal value, unfortunately, the horsepower will drop as well. If the torque required is greater than that available at peak horsepower, the rpm's will drop, which increases the torque to a value equal to that required (up to a point after which stalling would occur.) Unfortunately, the horsepower drops in that case as well. So, if I knew I was going to be cutting a certain type and size of wood, and I had just the right combination of sprocket teeth and chain, etc., horsepower would win every time. But now I switch to a bigger bar, a duller chain with more raker depth, a bigger log and different species of wood, and I need a saw with a broad rather than peaky power curve in order to maintain a similar level of performance. I've often thought (in looking at dyno charts of dirt bikes) that the total area under the horsepower-rpm graph means as much as the peak horsepower. I think one would need a horsepower-rpm graph of a saw to reach any conclusion without actually cutting.

As for the heavier flywheel, it acts as an energy storage device. That lag time in reving the engine that BW was talking about comes from the fact that all that rotational inertia is storing up energy. (Think of those little toy cars with the flywheel, takes a while to get the flywheel spinning fast, but then they go forever) So when you hit a tough spot with that saw, you have the power of the engine, as well as the energy stored in the rotating masses, to pull through the cut, for a while anyway, until the rpm's drop because you have consumed your stored energy.
 
if a heavier flywheel makes no difference, then try this. get a 200 pound flywheel off a john deere, rig it up on a free wheeling axle, spin it up to 500 rpm's, remove the power source, then grab hold of the shaft and try to stop it. that is called inertia. stored energy. it does make a difference. however, obviously, there are a lot of other factors to consider when designing a flywheel. if you were willing to wait a few seconds for your saw to rev up, with say a 10 pound flywheel, you would definately see a difference in the torque of the saw, but more importantly, the power band would be greatly altered. well, that wore me out for the night.
 
I was just thinking of the analogy to hybrid powered cars. The idea is to use a small engine with just a little more power than is needed to propel the car at road speeds. As your traveling down the road at cruising speed, that little extra available power is being stored off somewhere else so that it's there when you need it to accelerate hard or drive fast for a short time. Most hybrid cars are hybrid-electric, where that energy storage device is a battery, but I believe I saw an article once where a hybrid car was using a rotating flywheel for the same purpose. Then you keep that small engine operating at its most efficient rpm almost constantly.
 
tony m,, u have my respect. iu explained it in a way that was easy to understand.
oakman, this getty fellow had it figured right ,,,i figure. so wonder if he ever used the knowledge he had aquired. i do...aint scared o hard work ,but i only got so many hrs an days left.,, and by golly im gonna get the most i can outa everyone ofum. tip .. the best starting point ive found,for doing this ,,,is to determine to be a positive in the life of everybody u meet. [today] sometimes
all it takes is a smile...u can do this without being a goody two shoes. if u lear how.
 
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BWalker, Granted! I have supposed that crank and flywheel weight makes a difference on saws but not a significant one at all. I thought/think that the real differences must be porting and other design aspects.-Just trying to gain a better understanding of it all.:)
 
To add to Stumpers comments on Nicisil. NS coatinga are much harder, adhere much better, resist corrosion better, actually attract and hold oil, and last much longer than Chrome. Chrome sheds lube, peels easily, has corrosion issues, galls easily. The reason Echo, Shin, Redmax and others use cheom is because in Japanraw materials cost much more. As a result the japs enginner things cheaper as compared to there european counter parts. Things like chrome cylinders and few fitted parts are typical of japanese design that help them remain cost competitive.
 
More bore = faster revs, higher RPM
More stroke = more torque, lower RPM

Long rods have lots of leverage, big bores have a big combustion chamber, and less travel, so more revs, faster:clap:

Consider boring, Vs stroking an engine:)
 
Do Stihl's have more low range torque than Husqvarnas?HORSELOGGER,sir my power equipment dealer(Husqvarna and Shindaiwa) while on vacation in Maine last spring dirt bike riding said the Shindaiwas were very popular with loggers there.I have a 488 and am happy with it,though I'd like to get something bigger also.The only two downsides with Shidaiwa is that dealer support may not be to good in some areas and that they might vibrate more than a Husky,Ron K.

what dealer did you talk to. ive never seen a shandaiwa in the woods. only saws i ever see are husky and stihl, every now and again i see a Jred.
 
...

I see the Shindaiwa 757 makes peak hp at 9000 rpm and I can get one new for 575 bucks, but I have not ever spoken with anyone that has logged with one. I searched the site here and found one guy refer to using it in a tree service environment, but that aint the same as luggin er all day. Anybody else use one?

Had one for about 11 years. Good saw. I think it has more guts in a cut than my Husqy 272, but not as light. Repairs are easier on the controls, and not needed as often. It has had problems keeping the mufflers on, but that seems to under control for now.

My guys perpetually don't use it as much because it isn't a popular color.
 

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