Relationship between HP and cut times?

[timberwolf]

I am wondering about the relationship between HP and cut times.

Lets take a 4hp stock 50cc saw and a 10 inch block of softwood, say it cuts it in 4 seconds.

So if we now mod the saw, and it cuts the wood in 3 seconds, that is a 25% reduction in cut time. So is it safe to say that this is now a 5 hp saw?

Or is it just not that simple, what if the for sake of argument the saw produced the same 4 hp but instead of producing it a 10,000 rpm, it produces it at 12,500, a 25% increase in chain speed? But then to produce 4hp at a higher rpm torque would be lower, and would the saw be able to be pushed as hard and cut as much per rev?

Might need to put the good old wood dyno up against one of the new high tech ones.

 

[bugfart]

I shaved way more than a second off of a saw for a guy by replacing his chain, bar and sprocket.

Hard to believe a C-72 could be that much better with 3/8 instead of .404, but it is.

Just a more than one way to skin a weasel storey but I believe you are on the right track. I can advance the timing a scoche and get a similar result.

I don't believe these things are linear, or that predictable in case anybody here is from Rochester NY. (I'm on my way there Saturday, just teasing) But it seems the 4 and under saws get the most benefit. Even the old muscle saws seemed to get a little deminished returns above 6 HP.

Maybe because the thinner kerf of the smaller saws transfers to a larger perceived gain? Just to tie these thoughts together.

Electricity has firm relationships between voltage and current on a linear scale, they are referred to as "inverse" values. Could speed and power be the same? Great thread if I have not muddied it.

 

[Crofter]

With a car, any increase in percentage speed takes a far greater percentage horsepower increase because the wind resistance increases as the square of the speed. Boats might take even greater horsepower input ratios for speed gains. Maybe cutting wood is closer to being linear.
Now just to muddy the water, if the chain and bar resistance is the same at say 10,000 rpm for both a 260 and a 660, would an addition of 2 horsepower to each, have the same effect in reducing their respective cut times?

 

[bugfart]

Well, I'm not sure we can just say HP.
If it already has enough HP way more would have no effect. RPM, now did we add speed? Did we oh... switch to a 8 tooth sprocket?

Maybe it's all about the sprocket-rocket, and HP needed to use it.

 

[wagonwheeler]

Certainly, either increase the amount of work in the same time or decrease the time for the same work. You'd have to know you were optimized in each case to make it conclusive. And you were not just getting theoretical work done.

I guess that's why everyone touts thier best HP numbers, but when you find out where they measured it it may not be so relevant since in some cases max HP isn't where the work gets done.

 

[bump_r]

I'll go along with a statement that there is a linear relationship between HP and the ABILITY to reduce cut times, but I'd think that the increased HP would have to be better used, to some extent.

If, for example, a chain's kerf, grind characteristics, depth setting and the like are the bottlenecks to a timed cut improvement, (as opposed to power, technique, or RPM) throwing more HP at that chain would have little effect. Optimizing the chain to take advantage of the increased HP would be key. Back to the drag car analogy - if the tires were the limiting factor in a 300 HP car, throwing in a 600 HP engine wouldn't help the ET as much as that engine AND tire improvements.

What I guess i'm (quite poorly) trying to suggest is that there may be a HP combination where the chain is cutting at it's maximum speed at a given chainspeed. Increasing HP alone would yield no improvements - you'd need to alter the chain itself or some other variable. Up until this theoretical ceiling is reached, there should be some predictable inverse relationship between HP and cut times.

Just thinking out loud, sorry to muddy up the thread.

 

[wagonwheeler]

Now just to muddy the water, if the chain and bar resistance is the same at say 10,000 rpm for both a 260 and a 660, would an addition of 2 horsepower to each, have the same effect in reducing their respective cut times?

No. 260 would benefit more. Dunno how to explain why, though. Stroke, torque, etc... 660 just wouldn't notice as much.

Take 2hp away from each and see which would notice more, right?

 

[timberwolf]

% gains, the 260 uses poportionally more of it's power just to move the chain and internal parts.

2 HP on a 260 is like en extra 50%
2 HP on an 066 is more like 20%

May be if HP is created at a higher RPM it can be used, with a small sprocket and a narrow kerf race chain with a high raker setup. But would it not then be better to make a bit more HP where there is some torque left and gear up to get the chain speed, at lower rpm there are lower engine losses and the engine might last a bit longer.

 

[bugfart]

Ditto.
Right now I'm looking to just that.