horsepower vs. displacement

[gpanseri]

what is more important to look at when researching chainsaws the horsepower or cc's? and what really separates a homelite or poulan from the stihl's and husky's? i know they run a higher fuel to oil ration, but will my 53.6 cc homelite 330 perform differently from a husky of the same displacement (my 330 is 32:1 fuel to oil ratio)? thanks for all your help everyone i know that i ask alot of questions

 

[Grande Dog]

The most current rating is the power to weight ratio. Just like anything else, only as good as the specifications the manufacturers supply.

Grande Dog
Master Mechanic
Discount Arborist Equipment and Tree Care Supplies

 

[glens]

Yeah, the power:weight would be a good comparative value if the manufacturers all used the same methods to measure the weights and power of their saws.

The fuel:<i></i>oil values are really insignificant.

After doing all the catalog/web shopping, you really need to get into the showrooms and check them out first hand.

What saws are you currently considering and why?

Glen

 

[Kenskip1]

First I would like to say that as far as questions go, this one has made it to the top of my list. This is the pinnacle of question! My congradulations.
Now from time to time I have had the good fortune to offer bits of wisdom and down right sound advise. However, this is not one of them. Your question has me somewhat perplext. Nothing like a challange is my motto so here goes!
The most easliy comparison that I can give would be using a Dodge cumming diesel as an example. This engine has a rather low horsepower rating, but has a huge amount of torque. A long stroke that makes the engine turn slower, but the amount of pull is what makes this engine so popular.This is what makes the power plant so popular. I believe that this engine has about 300 cubic inches.
Now look at chain saw engines.If you want a saw that has a lot of low speed torque, simply look at the specs. Some saws turn at over 14k. This will generate much heat and horsepower however at a rather lower torque ratio. Other saws turn at around 95k. This saw may have lower horsepower but has gobs of torque.
So how do we balance this out? Gearing is the simplist remedy. A saw that turns slower will have more torque so we are able to use gearing to speed up the chain.
Now today, many saws have a compression release. Does this give you a clue at to what side of the equasion this is headed? If you said higher horsepower you are correct. It is cheaper for the manafacture to make a smaller engine that turns faster than one that turns slower.More horsepower means a higher compression ratio, hence the compression release. Higher RPM means more heat generated than the lower RPM with less heat generated.
Simply to put this in a nut shell one will have benifits over the other.
I take full credit for this composition. I hope that I have shed some light on to your excellant question.
Ken, PHD. (piled higher and deeper)

 

[BigSawMan]

Other saws turn at around 95k. This saw may have lower horsepower but has gobs of torque.

I do hope that you mean 9.5K, I yet to see a chainsaw engine go 95,000 RPM without it grenading, its impossible. EHP I belive had an 090 that turned 18,500 rpm but it would just keep going higher and higher in the rpm's untill it grenaded. I belive that it was all a matter of getting all of the figures and measurments to equal out and have the clearences like super correct, then the engine would just wind up will it blew, course these were hotsaws, so they dont need to run more than 5 seconds at a time, there is no place for that in a woods saw.



Scary thoughts.

Neil

 

[glens]

Originally posted by Kenskip1
The most easliy comparison that I can give would be using a Dodge cumming diesel as an example. This engine has a rather low horsepower rating, but has a huge amount of torque. A long stroke that makes the engine turn slower, but the amount of pull is what makes this engine so popular.This is what makes the power plant so popular. I believe that this engine has about 300 cubic inches.

The engine is a Cummins, not anything to do with Dodge except Chrysler buys them for their vehicles.&nbsp; Right?

Horsepower in an engine is strictly a function of torque and RPM.&nbsp; The values of torque in pound-feet and horsepower are always the same in any engine spinning about 5200 RPM.&nbsp; Below the crossover point, the torque values will be higher than the horsepower; above it the opposite occurs.

A long stroke does not make an engine turn slower.&nbsp; Most of the time with two engines of the same displacement and differing strokes, the one with the longer stroke will produce more torque at lower RPM (and the other more torque at higher RPM), but that's not set in stone.&nbsp; There are several other factors at play.

What (evidently) makes the Cummins engine in the Dodge trucks so popular is the combination of torque over RPM combined with the transmissions and rear ends to produce usable gearing and power combinations.

So how do we balance this [RPM at which optimum power is produced] out? Gearing is the simplist remedy. A saw that turns slower will have more torque so we are able to use gearing to speed up the chain.

An engine that can perform a certain amount of work at a lower RPM as another at a higher RPM does not necessarily mean one's better than the other.&nbsp; They're both doing the same amount of work, but the one designed to run at the lower speed will require heavier components to accommodate the fewer, stronger, pulses.

Now today, many saws have a compression release. Does this give you a clue at to what side of the equasion this is headed? If you said higher horsepower you are correct. It is cheaper for the manafacture to make a smaller engine that turns faster than one that turns slower.More horsepower means a higher compression ratio, hence the compression release. Higher RPM means more heat generated than the lower RPM with less heat generated.

I'm lost...&nbsp; The same amount of heat will be produced either way unless one engine is more efficient than another.&nbsp; It's possibly correct to say a smaller, higher-revving engine can be made more cheaply than the alternative, but that comes down to the necessary strength (heft) of the components again (in part).&nbsp; The compression release is more likely an indicator of the strength of the starter components and/or ergonomics than of engine strength.&nbsp; In any event, a smaller, lighter engine which can do the same amount of work in any given timeframe is to our [the users] benefit as well.

Glen

 

[Kenskip1]

Yes I made an arror 9.5k or for people in NY ( Joker) 9500 Revolutions Per Minute, Yes I have made an error or to in all of my youthful years. Ken

 

[BigSawMan]

The engine is a Cummins, not anything to do with Dodge except Chrysler buys them for their vehicles. Right?

Yeah, I belive they just buy them, and install them, thats it. They dont make the engines, but they might give Cummins some tips for making it, if it was like specifically made for the pickups, but I doubt it.

 

[Kenskip1]

glens
Well here we go. Plain and simple.A higher compression requires more fuel per stroke than a lower compression. A prime example would be goin back to the late 70's. A higher compression Chevell had great horsepower that used more gas. A lower compression engine uses less gas. less gas is simply a lot less heat generated. A higher compression HuskyXP uses gas more quickly than a standard run of the mill saw. I will use my 028 as an example.Ken

 

[Shade]

the compression ratio has very little to do with fuel consumption.

air:fuel ratio is what burns good, the gas has no idea what compression ratio the engine is. higher compression ratio's typically need higher octane ratings, but that's due to the possibilities of pre-ignition, or knock, which eats pistons, and tears things up (similar to lean type damage).

 

[BigSawMan]

Whats the octane raiting on aviation fuel?

Neil

 

[bwalker]

Whats the octane raiting on aviation fuel?

The most common avgas is 100LL and it is not rated using the traditional R+M/2 method. Rather it is rated using the astm rich/lean scale. On that scale it is rated 100. On the R+M/2 scale it would be significantly less than 100. Maybe around 95-97?

RE Cummins. The Cummins is popular powerplant for dodge trucks because it is a medium duty engine offered in a light truck. It has no equal when it comes to durability, economy and resale value. It is also very popular because it has the traditional low rpm diesel power curve and as such pulls heavy loads very well.

Glens is quite right the stroke alone isnt a indicator of a high torque motor. Torque is basicly a measure of cylinder filling efficiancy and as such things like cam timing, turbo boost, exhaust and intake type all have a influance.
Thats being said most long stroke motors have low rpm torque biased power curves. This is mostly due to the effects of piston speed on wear and reliability as the rpms rise. For fun calculate the piston speed of a cummins at 13,500 rpm. It will scare the bejesus out of you.

FWIW the current Cummins as offered in the Dodge ram is rated at over 300hp so its hardly a low hp engine. It aslo has displaced 360 CI since it was introduced.

 

[bwalker]

A higher compression motor is more efficient and as such should use less fuel....
The anology between the 028 and Husky xp isnt valid. As the Husky of the same size is better on fuel than the 028. Not because of compression, but because the port layout is much better than the 028(and stihls in general). Higher reving engines in genral have lower compression ratios due to the parasitic pumping loses that occure at high rpm. It is very likely that a MNodern chainsaw has the same or lower compression ratrio than the old, gear drive torque monsters.

 

[ehp]

It was not me that said you can get a 090 to that rpm cause the crank will break long before that rpm is ever made



i think you need to look at the job that the saw has to do before you can say what is better, torque or rpm's , you have to gear the saw to get the best out of both deals and file the chain to the best from each saw, that is why i am not one for 1 chain on all saws for a test cause each brand is different and you are not going to show there full power

 

[geofore]

important?

Most important is what are you going to be asking the saw to do for you? Any good saw can be tweaked to get more out of it but if you don't know how to use the saw or what you're going to use it for, more is not better. What kind of wood will you be cutting and how big a bar you intend to use? Then the chain, has to be sharp, no matter what style chain you use and that makes a difference. Can you file square or round chain? Are you going to be racing, logging, firewood or trimming? Are you using the same saw for all these jobs (all purpose saw) or do you have a different saw for each job? After you know what you want the saw for then ask if it takes horsepower or displacement to get the job done. Are you a weekend worrior, everyday it's my job saw user or homeowner I only use it once in a while guy? Horsepower vs Displacement are relative if you're going to send your saw out to be ported because your going to tell the builder what you want, Low end torque or high end torque because the builder is going to ask you what you intend to use the saw for if you don't tell him first. Your question sounds more like you want to ask if the more money it costs for the Stihl, Husky, Dolmar or Johnny is worth spending. It is if you are using the saw for work every day. You comining to the Pittsburgh show or what?