Another chainsaw dyno...

[MustangMike]

Thanks for the info Dave, I was thinking your cylinder was AM. FYI, mine was not a Big Bore.

IMO, those Asian 660 bottom ends do hold up well. If they resolve the chain adjuster issues they will be nice!

 

[MustangMike]

As much as anything it is the shape of the torque curve that dictates a saws manners, not absolute numbers, and having a flat torque curve also has a drawback for a chainsaw.

Warning, Opinions inbound.

Flat torque curves give you high power, as they better maintain torque to higher rpms, but the flatter the torque curve the less of a torque boost there is to help maintain RPM when extra load is applied, hitting a knot, bar pinch, shifting extra force onto the bar, etc, effects that can be more pronounced with a longer bar.

A torque curve that drops off more substantially from peak torque to peak horsepower will better self regulate speed than a flat torque curve with minimal user input.

I would use a stock 395 vs 660 chart of the same HP to describe my thoughts, but didn’t see one.

The stock 395 vs SCARR 395 illustrates it well enough though, and I mean NO negativity to any saw, it’s just what happens when you perform these kind of mods.

I don't know if I have ever issued a Best Answer before, but your post deserved it and stated what I was thinking but not properly expressing.

Hp will increase cut speed, but big low end torque will inspire confidence in your saw. I really like using my Asain 660 for ripping large Oak and hard Maple rounds. I can lean on it, and it just does not quit. (Plus, it cuts faster that my other660s, seems to have more RPMs).

As you can see the ported 395 has a nice flat torque curve leading up to peak power, the stock saw dropping off more rapidly.

The ported saw has more torque everywhere, so it will of course pull the chain harder at all times, it looks like a great machine.

But let’s consider a scenario, both saws cutting at 9400rpm when a very slight bar pinch occurs, More load is placed on the chain, more torque is needed at the sprocket, the chain slows down.

Now let’s say the lightly pinched chain requires 0.2ftlb more torque at the sprocket to match the new load, simply trace the torque chart from the before pinch rpm (9400rpm), add the (load) torque increase that occurred (.2ftlb) and find the new rpm that results, as long as the saw can produce the needed torque figure anyway, and we are talking no adjusting bar/cut pressure, just letting the saw take care of itself.

Stock saw, 3.8ftlb @ 9400rpm to 4.0ftlb, rpm drops to 8750.

Ported saw 6.0ftlb @ 9400rpm to 6.2ftlb, rpm drops to 7200.

While the ported saw will drop more RPM it will still be outcutting the stock saw as it still maintains a power and torque advantage but will some perceive the stock saw to have more torque?due to how easily it deals with deals with load increases, not dropping many rpm.

When operating past peak torque, like we do with a chainsaw flat torque curves do not provide as large a torque reserve to maintain rpm for load increases.

And I imagine the Dyno will show older larger saws that get dyno’d, the ones that love getting dogged in and are described as unstoppable will have far from flat torque curves, that their unstoppable nature is that they have a large torque reserve/increase to give as RPMs are pulled down..

Machining steel, you have to stay within the thermal limits of your cutting tools, an issue we don’t have.

 

[Spladle160]

Flywheels have nothing to do with torque. Rotating mass has nothing to do with torque. Zero, zilch nadda. They are unrelated. As google puts it.

A rotating flywheel having more mass than another, both spinning at the same RPM, has more energy than the other, not more torque. The engine must be under a load to produce torque, and the torque is independent of the flywheel weight. ... Heavier flywheel = more drivability, lighter flywheel = greater acceleration

Theoretically you should get the exact same dyno graph with a heavy or light flywheel. In the real world the lighter flywheel saw will take less to accelerate and the heaver flywheel saw will take more to stop.

 

[RI Chevy]

Let's try it and see...

 

[wcorey]

But let’s consider a scenario, both saws cutting at 9400rpm when a very slight bar pinch occurs, More load is placed on the chain, more torque is needed at the sprocket, the chain slows down.

Now let’s say the lightly pinched chain requires 0.2ftlb more torque at the sprocket to match the new load, simply trace the torque chart from the before pinch rpm (9400rpm), add the (load) torque increase that occurred (.2ftlb) and find the new rpm that results, as long as the saw can produce the needed torque figure anyway, and we are talking no adjusting bar/cut pressure, just letting the saw take care of itself.

Stock saw, 3.8ftlb @ 9400rpm to 4.0ftlb, rpm drops to 8750.

Ported saw 6.0ftlb @ 9400rpm to 6.2ftlb, rpm drops to 7200.

While the ported saw will drop more RPM it will still be outcutting the stock saw as it still maintains a power and torque advantage but will some perceive the stock saw to have more torque?due to how easily it deals with deals with load increases, not dropping many rpm.

When operating past peak torque, like we do with a chainsaw flat torque curves do not provide as large a torque reserve to maintain rpm for load increases.

And I imagine the Dyno will show older larger saws that get dyno’d, the ones that love getting dogged in and are described as unstoppable will have far from flat torque curves, that their unstoppable nature is that they have a large torque reserve/increase to give as RPMs are pulled down..

Seems to me the basic flaw/omission in this theory is that when the pinch/load requires the specific amount of additional torque to maintain rpm, it’s relative to the output.
The 4 ftlb saw needs it to keep going but the 6ftlb saw already has it (and more).

 

[Sawrain]

Seems to me the basic flaw/omission in this theory is that when the pinch/load requires the specific amount of additional torque to maintain rpm, it’s relative to the output.
The 4 ftlb saw needs it to keep going but the 6ftlb saw already has it (and more).

I did consider that, as I was at first going to build my theory on percentage load increases per saw, not absolute figures as I did, anyhow, my thoughts were as follows.

Again considering both saws in the same cut.

Cutting steady state at 9400rpm, the ported saw is cutting much faster than stock with an optimised chain taking more/bigger chips, removing more material, it’s faster cutting uses all the torque the saw can muster.

If there was more torque available the saw would be increasing in rpm, it isn’t, so both saws are operating at a point where the sprocket torque required to move the chain exactly matches the torque the engine is providing, this will be the torque plotted on the Dyno chart.

As for the pinch, if the cut is the same, and the side cutters are suddenly asked to remove X amount more material, it seemed reasonable that both saws experiencing the same pinch would have the same load added to them, even if one was cutting faster.

Basically my thought was that all torque is already being used to make make the original cut, so it’s absolute figure is not the most important thing, how much more torque the saw can muster as load is added is, in regards to how the saw responds to load increases/changes through a cut anyway.

I appreciate the thoughtful questioning.

 

[Cobby08]

Let's try it and see...

Such an instigator...

 

[Dub11]

I don't own any saws that make me cry
well except the KMS4

You killed the mini dorito?

 

[Definitive Dave]

You killed the mini dorito?

sadly the coil seems to be slowly failing

 

[cuinrearview]

A little birdietold me Joe has syphilis and won't be able to dyno my junk this weekend. I have the sads for you @Red97

 

[Definitive Dave]

A little birdietold me Joe has syphilis and won't be able to dyno my junk this weekend. I have the sads for you @Red97

Hyper-Syphilis I heard.

 

[Bigmac]

Sure, you can dog it in and get up on that rear handle. But at that point the chain plays a big factor. Will it run a 36” like a 395 or 066?
No it will not. It had a flat torque curve, but it stayed under 6 ft lbs if I remember right.

After looking over the graphs again, as a comparison of the hybrids to the ported 395, torque and hp is real close at 10k, the hybrid maintains is torque longer and the 395 has more torque under 10k. How do you feel the that difference plays out? Is that the torque under 9k irrelevant or dose that power available under the curve make the saw harder to drop in rpm? I get what your saying about 6k power, I am just wondering if that reserve torque keeps a saw from dropping rpm under load or is it irrelevant. It seems like it could be a factor, but maybe it isn’t. Like your hybrid versus Canadian farm boys hybrid, not that you would cut at 12,000 RPM but let’s say you did, would the increase torque below 12k of cfb’s hybrid make it want to hold 12k better?

 

[Deets066]

After looking over the graphs again, as a comparison of the hybrids to the ported 395, torque and hp is real close at 10k, the hybrid maintains is torque longer and the 395 has more torque under 10k. How do you feel the that difference plays out? Is that the torque under 9k irrelevant or dose that power available under the curve make the saw harder to drop in rpm? I get what your saying about 6k power, I am just wondering if that reserve torque keeps a saw from dropping rpm under load or is it irrelevant. It seems like it could be a factor, but maybe it isn’t. Like your hybrid versus Canadian farm boys hybrid, not that you would cut at 12,000 RPM but let’s say you did, would the increase torque below 12k of cfb’s hybrid make it want to hold 12k better? View attachment 254023View attachment 254024

Those are good questions, that I have no answers for, only speculation.
Torque definitely dictates the “manners” of a saw. That torque that’s lower may not be irrelevant, but the saw may cut better/tune at lower rpm than a saw with torque at a higher rpm.
A guy would really need to run em side by side to even get a seat of the pants feel.

 

[Dub11]

sadly the coil seems to be slowly failing

I've herd tale from some of these classic mag saw dudes that baking the coil can "restore" them.

I think it was @sawnami that mentioned it before.

 

[Deets066]

I've herd tale from some of these classic mag saw dudes that baking the coil can "restore" them.

I think it was @sawnami that mentioned it before.

Only baking that Dave does is cookies or brownies.

yum.... turtle brownies.....

 

[sixonetonoffun]

I've herd tale from some of these classic mag saw dudes that baking the coil can "restore" them.

I think it was @sawnami that mentioned it before.

I did an old Remington SL5 coil that was all crackled coating but also wrapped it in electrical tape.

Not sure how long term the fix is will be. Luckily there are a couple other coils that work in those still available. But even the homelite coils are close to the value of those old door stops.

 

[wcorey]

...would the increase torque below 12k of cfb’s hybrid make it want to hold 12k better?

Assuming I understand the question correctly...

Kind of a chicken/egg thing potentially.

One way to look at it is the only torque that has any relevance at all in the cut is the torque at the present running rpm, its the only torque that exists after all... the torque below the rpm you're running is purely hypothetical at that point in time and only exists once you get dragged down to that rpm.

Unless you can maintain the cut simultaneously in multiple parallel time skewed dimensions maybe, lol.
No, I'm not smoking anything...

Now once you start getting pulled down in rpm, some increased torque there most certainly helps to recover from the increased load that put you there, so gets you back to peak power/rpm quicker, if that's what you meant...

But that's all obvious so I dunno, maybe I'm reading too much Kenny...

 

[Egg Shooter]

A little birdietold me Joe has syphilis and won't be able to dyno my junk this weekend. I have the sads for you @Red97

Should have worn a mask over his pee pee.

 

[Deets066]

Assuming I understand the question correctly...

Kind of a chicken/egg thing potentially.

One way to look at it is the only torque that has any relevance at all in the cut is the torque at the present running rpm, its the only torque that exists after all... the torque below the rpm you're running is purely hypothetical at that point in time and only exists once you get dragged down to that rpm.

Unless you can maintain the cut simultaneously in multiple parallel time skewed dimensions maybe, lol.
No, I'm not smoking anything...

Now once you start getting pulled down in rpm, some increased torque there most certainly helps to recover from the increased load that put you there, so gets you back to peak power/rpm quicker, if that's what you meant...

But that's all obvious so I dunno, maybe I'm reading too much Kenny...

That’s kinda how I see it.

 

[Bigmac]

Assuming I understand the question correctly...

Kind of a chicken/egg thing potentially.

One way to look at it is the only torque that has any relevance at all in the cut is the torque at the present running rpm, its the only torque that exists after all... the torque below the rpm you're running is purely hypothetical at that point in time and only exists once you get dragged down to that rpm.

Unless you can maintain the cut simultaneously in multiple parallel time skewed dimensions maybe, lol.
No, I'm not smoking anything...

Now once you start getting pulled down in rpm, some increased torque there most certainly helps to recover from the increased load that put you there, so gets you back to peak power/rpm quicker, if that's what you meant...

But that's all obvious so I dunno, maybe I'm reading too much Kenny...

I was bringing up the torque under peak, as a reason some of these saws like a 395, might over preform compared to the “dyno” numbers. Many ported 60cc saws have more hp than a stock 395, and there may be a few 50cc saws that have more as well. Is it solely rotating mass that makes the difference in performance? Could adding flywheel weight alone take a 60cc with 7 hp and turn it into an equal to the 395? It has been brought up the rotational mass has zero effect on dyno numbers, I actually feel the heavier weight would take more hp to turn. Theoretically if an engine didn’t have enough power to turn its own mass, would it run? Or dose it just take a life time to accelerate? So that make me feel there has to be losses for rotating weight. But it may not be that noticeable on the dyno. And if it’s not rotating mass, then it has to be torque under the curve?

I am just curious to some of these crazy details, I also don’t own a 395. Lol