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. Right?
Horsepower in an engine is strictly a function of torque and RPM. The values of torque in pound-feet and horsepower are always the same in any engine spinning about 5200 RPM. 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. 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. 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. 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... The same amount of heat will be produced either way unless one engine is more efficient than another. 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). The compression release is more likely an indicator of the strength of the starter components and/or ergonomics than of engine strength. 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