Torque Vs RPM

[Freudianfloyd]

This may sound like a really stupid question, but watching some of these V8 powered saws cutting, got me to thinking.

These engines obviously put out a ton of power, but is all that power actually being utilized? I'm assuming these V8 are probably running around 9,500 RPM, maybe. And producing hundreds of ft. Lbs of torque, but how much of that gets into the cut?

What I haven't seen is somebody take a smaller 4 cylinder motorcycle engine, like a Hyabusa, which still puts out quite a bit of power but much less torque, with a much higher rpm say 13,500 rpm.

Is that V8 necessary, or is the whole point just to be ridiculously huge which looks cool, or is that engine actually necessary for what they are doing?

If this is a stupid question, I apologize, I'm just curious.

 

[anlrolfe]

I once had an avid car collector, racer & engine builder, tell he that horsepower is how fast you can hit the wall, torque is how far you move it...
Are you letting the sharp chain and weight of the saw do the work or leaning into it. Milling or cross cut???

With a car weight and acceleration will require both HP and Torque. For something light, the ability to turn up RPM quick vs roll slow and lumbering like an ox leaning into a draft load, diesel or work truck with a granny gear grunting at low RPM.

I tend to see HP as how fast you can accelerate a given load and torque how much load you can sustain at a given RPM

 

[anlrolfe]

Military is working on 3cyl Horizontal opposed 2-cycle turbo diesels. Compromise power and fuel efficiency.

In Napoleons time they said the army traveled on its stomach. I learned in the Marine Corps that you needed 3 things for battle 1)beans 2)bullets 3)bandaids . The truth is that the military travels on diesel and J P - 1

 

[full chizel]

RPM is how fast you hit a wall....torque is how far you move it.

 

[Freudianfloyd]

I understand, but are these V8s actually using all that torque or are they over kill.

For example, I guarantee my Stihl pole saw could cut through a small twig as fast as my 660 on the same twig. Neither of which is being used to their full potential. The pole saw revs like crazy, the 660 has a ton of torque.

Unless those V8s are using every ounce of power, and maybe they are, it seems you could cut just as fast with a quicker revving less powerful saw.

Again, maybe I am just making myself seem more ignorant on the subject.

 

[buzz sawyer]

Interesting question but honestly, I'm just impressed with someone building and lifting a V8 chainsaw.

 

[Ted Jenkins]

I have messed around with many high performance motorcycle engines that produced an impressive amount of power. They however needed gear boxes because they produced no torque to speak of. Some ran in the low 20,000 RPM category so they could not get out of their own way with out lots of gears. Many V 8's are a compromise of torque power displacement and ease of operation. Certainly more gentle than the V 12 P 1710. I think the biggest engine I worked on had 400 HP with turbo charger on a bike, but not too much torque. Thanks

 

[Huskybill]

A Suzuki 400 cc bandit motorcycle redlines at 17,000 rpm.

 

[trappermike]

Horsepower happens at high rpm,torque occurs at a much lower rpm.On my saw dyno I found that a 100cc work ported saws made max torque at 8500 rpm,max horsepower around 11,000,the fastest cutting speed is somewhere in between depending on the engine.

 

[PakProtector]

Torque is how hard you can push. Power is how fast you can push. Hard push can move much, but if no power it is not going to happen quickly.

A high rpm engine, with a lot of power usually has a fair bit of reduction so as to deliver enough 'push' or in this cast torque( by multiplication by the gear ratio). Acceleration takes power. P=m*v*A. So keeping the same acceleration rate at 20 mph as you have at 10 requires 2x the power.

A torquey turbo-diesel( 6BT-5.9 example ) just has more low end POWER than some of the other options. That the RPM is so low( compared to the usual spark-ignition suspects), we see torque numbers that look very impressive.
cheers,
Douglas

 

[Huskybill]

Horsepower happens at high rpm,torque occurs at a much lower rpm.On my saw dyno I found that a 100cc work ported saws made max torque at 8500 rpm,max horsepower around 11,000,the fastest cutting speed is somewhere in between depending on the engine.

Most ported saws we hear sound like stock saws. The cut very slow.

 

[Haironyourchest]

No engineer, me, but I would think the V8 saws are not even scratching the surface of their potential power. The cutting performance is limited by 2 things, chain speed and cutter performance.

Chain speed is a function of horsepower in a direct drive transmission, but with gearing torque would easily replace hp. I'm guessing the V8s are direct drive? How much hp does a V8 output, 600? With a gearbox, one could probably achieve a chainspeed rpm of easily 100 thousand rpm. I'm betting a saw chain would not withstand these forces and something bad would happen. Regards the cutter performance, the second way to remove more material is to have bigger cutters. Bigger cutters. Means bigger drive links, bigger, heavier bars. More resistance, which is where you'd need torque over hp. But to level up the cutting assembly to the point where it was maxing out the available torque of a V8, I would think a couple of humans wouldn't be able to handle it. Plus you'd need the matching amount of force into the wood to take advantage of all that torque, which humans would not be able to provide.

So, from my totally unqualified position, it looks like the V8s are mostly show, probably 80-90% wasted power.

 

[Chainmale]

Power is torque X speed (RPM)

 

[holeycow]

No engineer, me, but I would think the V8 saws are not even scratching the surface of their potential power. The cutting performance is limited by 2 things, chain speed and cutter performance.

Chain speed is a function of horsepower in a direct drive transmission, but with gearing torque would easily replace hp. I'm guessing the V8s are direct drive? How much hp does a V8 output, 600? With a gearbox, one could probably achieve a chainspeed rpm of easily 100 thousand rpm. I'm betting a saw chain would not withstand these forces and something bad would happen. Regards the cutter performance, the second way to remove more material is to have bigger cutters. Bigger cutters. Means bigger drive links, bigger, heavier bars. More resistance, which is where you'd need torque over hp. But to level up the cutting assembly to the point where it was maxing out the available torque of a V8, I would think a couple of humans wouldn't be able to handle it. Plus you'd need the matching amount of force into the wood to take advantage of all that torque, which humans would not be able to provide.

So, from my totally unqualified position, it looks like the V8s are mostly show, probably 80-90% wasted power.

they sure cut damn fast. I betcha they are using more than 20%.

interesting question op.

Apparently no question is a stupid question, even that one. Haha!

 

[Huskybill]

V8? What more saw do you need than a 2100 ported and tuned?

My sons suzuki bandit was a destined gixer 400 with 17,000 redline. Made for the European market. She beat the v twins no problem. Even 600’s but anything bigger beat him. A 400 in a chainsaw would be awesome.

 

[PakProtector]

V8? What more saw do you need than a 2100 ported and tuned?

My sons suzuki bandit was a destined gixer 400 with 17,000 redline. Made for the European market. She beat the v twins no problem. Even 600’s but anything bigger beat him. A 400 in a chainsaw would be awesome.

A tuned up RZ350 might *JUST* be carry-able. For sure one of the last liquid-cooled 250's for sure would be and there is about 50hp at the crank with a tune mild enough to drive a chain.
cheers,
Douglas

 

[ironman_gq]

A tuned up RZ350 might *JUST* be carry-able. For sure one of the last liquid-cooled 250's for sure would be and there is about 50hp at the crank with a tune mild enough to drive a chain.
cheers,
Douglas

You can get 50hp out of a 250 2-stroke dirt bike engine, the Honda CR250R motors peaked at a claimed 58hp from the factory. Those are very easy to turn into a saw, they even run at the right RPM's for pulling a chain.