Porting torque vs hp

[Iron.and.bark]

Interesting posts guys

Now my issue is with the fact that porting/modding a saw seeking more torque is pointless. I actually wanted to title the thread rpm vs torque, but choose to respond to a statement that had been made.

My 3120 story.

Got myself a nice 3120, fixed carb,stock muffler and unlimited coil we have over here.

Slabbing in an alaskan mill. 8 tooth sprocket, 3/8 skip tooth chain (credit me with know how to setup a milling chain properly) and ~30" log. When fed in carefully would cut, apply to much pressure and it stalled and burnt up the clutch. Saw does never reach max rpm and hence max HP.

Switched to 7 tooth sprocket, saw would still stall and could not fully lean into milling cut.

Modded muffler.

Switched to full comp, saw cut at same speed (around ~8-9k rpm) and obviously milled faster due to more cutters. Could still bog if you tried Really hard to.

Pulled cylinder and widened exhaust port (not raised).

Full comp, 8 tooth .404 was able to be run. It liked it

Now what had increased?

Not rpm as it remained approximately constant.

Since as the "Boss" around here said

HP = torque x rpm

HP must have increased, and what enabled that was torque. When I say increases HP, I should clarify it by saying HP at that given point in rpm that the saw operated at.

A 2 stroke used in a chainsaw is a whole series of compromises. You are trying to make the best use of an imperfect machine to do an imperfect job and if you are like me an imperfect operator

My point being you can point the compromises in more than one direction as jobs go in more than 1 direction

Oh and when next summer we take out a section of 40yr old pines, I sure as hell would love a JMS saw

 

[RIDE-RED 350r]

This forum is like continuing education for me. You guys are teaching us old dogs new tricks.......and I love that.

Well, the "Old Dogs" aren't still around and competitive for becoming obsolete either... I too love and have benefited from the info sharing and help that is so readily available here.

 

[RIDE-RED 350r]

In my rookie opinion, I think building a "torque" (or should I say a broader peak torque curve that begins at a lower RPM) saw is easier than building a peak saw. I'm sure the pro builders here can do more elaborate things to up the ante, but a simple compression boost from a BG delete (or cutting the cylinder base if the particular model doesn't play well with a BG delete), squish band re-work and a muffler mod does make noticeable improvements to a saw's lugging ability, torque.

I would like any of the aforementioned pros to correct me if I am mistaken on the above statement.

 

[Mastermind]

Interesting posts guys

Now my issue is with the fact that porting/modding a saw seeking more torque is pointless. I actually wanted to title the thread rpm vs torque, but choose to respond to a statement that had been made.

My 3120 story.

Got myself a nice 3120, fixed carb,stock muffler and unlimited coil we have over here.

Slabbing in an alaskan mill. 8 tooth sprocket, 3/8 skip tooth chain (credit me with know how to setup a milling chain properly) and ~30" log. When fed in carefully would cut, apply to much pressure and it stalled and burnt up the clutch. Saw does never reach max rpm and hence max HP.

Switched to 7 tooth sprocket, saw would still stall and could not fully lean into milling cut.

Modded muffler.

Switched to full comp, saw cut at same speed (around ~8-9k rpm) and obviously milled faster due to more cutters. Could still bog if you tried Really hard to.

Pulled cylinder and widened exhaust port (not raised).

Full comp, 8 tooth .404 was able to be run. It liked it

Now what had increased?

Not rpm as it remained approximately constant.

Since as the "Boss" around here said

HP = torque x rpm

HP must have increased, and what enabled that was torque. When I say increases HP, I should clarify it by saying HP at that given point in rpm that the saw operated at.

A 2 stroke used in a chainsaw is a whole series of compromises. You are trying to make the best use of an imperfect machine to do an imperfect job and if you are like me an imperfect operator

My point being you can point the compromises in more than one direction as jobs go in more than 1 direction

Oh and when next summer we take out a section of 40yr old pines, I sure as hell would love a JMS saw

That's very interesting. If RPM increased, then the clutch would be holding tighter.......so......

I'm gonna think on this while I'm assembling this 262.

Gotta go feed at 1900 hours too......

 

[Termitebuffet]

That's very interesting. If RPM increased, then the clutch would be holding tighter.......so......

I'm gonna think on this while I'm assembling this 262.

Gotta go feed at 1900 hours too......

I just fed .....me [emoji13]

Zoo City Sawz

 

[CR500]

Beautiful saws,especially the 064.
I forgot to tell you that

Thank you!!!
Dolmar is a little rough externally but inside should of been MINT lol

Not sure if I will keep the wrap on the 7900......

I think the 7900 should relate well to this torque and HP topic. Not necessarily a toque monster but from the factory it has decent RPM holding capabilities which is my theory on why they are so good

I am astonished with the 064..... did not want to cut with it when it arrived haha. John is the one to thank for that saw. I tried cleaning but those older mufflers appear to hold a bunch chips and dust.

Maybe that is why they have a distinct smell?

 

[jake wells]

If you look at steam engines...they all had 100 times the torque as they did horse power. An early Whites steam car produced 25 hp and 600 foot pounds of torque. Crack the throttle and the thing would do 60 MPH faster than a gas engine car! Torque and HP are both important. Not enough of either and the performance goes down. So that's why you add displacement and get the best of both worlds!

remember steam engines make max torque at o rpms

 

[MustangMike]

I agree with what Dan stated. Torque (or a broad power band, if you will) is very important in a work saw. In cookie cutting, when you always keep the saw in it's top power band, HP will win, but in the real world, where wood has knots & crotches, and bars can get pinched, torque is very much appreciated.

 

[mdavlee]

In my rookie opinion, I think building a "torque" (or should I say a broader peak torque curve that begins at a lower RPM) saw is easier than building a peak saw. I'm sure the pro builders here can do more elaborate things to up the ante, but a simple compression boost from a BG delete (or cutting the cylinder base if the particular model doesn't play well with a BG delete), squish band re-work and a muffler mod does make noticeable improvements to a saw's lugging ability, torque.

I would like any of the aforementioned pros to correct me if I am mistaken on the above statement.

It's easy to raise the exhaust and transfers and make a higher peak power on the dyno than it would to have the same power across 4-5k rpm in a saw. Compression helps torque to a point and then it fights itself. Stumpy learned that on the 372s when he had some with 225-235 lbs of compression get killed by some with 160-180. Put a flat top back in and they all ran a lot better. Some of the best running 7900s I've built have the same compression as a stock one with tighter squish than stock.

 

[weedkilla]

One thing I learned while playing with tuning stuff and things on dynos is that the fastest bike/car wasn't always the one with the highest peak hp number. The way to "see" a fast engine on a dyno was to measure the area under the hp graph within the critical rpm.
That's of no help to the guys who have built lots of saws, as they just know what works, but it might help someone have a way of conceptualising what's going on.

 

[mdavlee]

One thing I learned while playing with tuning stuff and things on dynos is that the fastest bike/car wasn't always the one with the highest peak hp number. The way to "see" a fast engine on a dyno was to measure the area under the hp graph within the critical rpm.
That's of no help to the guys who have built lots of saws, as they just know what works, but it might help someone have a way of conceptualising what's going on.

That is very true. Setup is more of a factor than HP. A 12 hp saw with a bad chain can be eat up with a 8 hp saw and good chain.

 

[weedkilla]

That is very true. Setup is more of a factor than HP. A 12 hp saw with a bad chain can be eat up with a 8 hp saw and good chain.

True, but unless you are competing against someone else chain is constant. I'm going to file a chain tomorrow just about as well (or badly) as I did today.

 

[jmssaws]

That is very true. Setup is more of a factor than HP. A 12 hp saw with a bad chain can be eat up with a 8 hp saw and good chain.

Chain and tune is the biggest thing but it don't hurt to have all of it.

 

[Stump Shot]

...so it would be like how manufacturers display horse power of different models. A Pro version of same cc as a home saw has more horse power and the torque just comes along with the HP increase. Is this kinda the right way to look at it so to speak? Then having it ported ups the ante again. Starting to see the relationship here, I think. Light is on I just have a dim bulb.

 

[jmssaws]

The 066 i have that scarr ported come from a guy who said it was ok but thought it had more in it,the tune was killing it.
I tuned it and at the time it was the strongest I had ran and all it took was a minute and a screwdriver to turn a ok saw into a beast.

 

[paragonbuilder]

I've not ran a saw like Dan talked about
I find that a fast saw is fast with any setup. I never pry on one much though I'm more of a let the chain do it kind of guy. Pry on one all day will make you tired and then you'll get hurt.

Your 064 is a great example. And I know you've run it. I ran it with some other saws, .404, 36" sq filed, all the same bar and chain. In a nice 30" piece of oak I could pull the saw down slowly, not yanking on it, to below 8k, and it was strong. One of the saws I couldn't get below 10k, it would stall, and it wasn't much pressure. But it would hold more speed self feeding. I find a saw like that useless in the working world.



Sent from my iPhone using Tapatalk

 

[Red97]

...so it would be like how manufacturers display horse power of different models. A Pro version of same cc as a home saw has more horse power and the torque just comes along with the HP increase. Is this kinda the right way to look at it so to speak? Then having it ported ups the ante again. Starting to see the relationship here, I think. Light is on I just have a dim bulb.

This is where the printed specs can get misleading.

Example

2 60cc saws.
Both with 3 ft lb one is 500 rpm higher that will equate to a larger hp number for the brochure. But is it really the stronger saw?

As jmssaws mentioned with the 066. Is one manufacturer setting the tune a bit better?


This is where the "power band" length comes into play. And you will never know till you run the saw personally.

That is my main goal with any saw I build, make the largest powerband possible. Haven't done enough saws to have it down pat, but the saws I have done turned out quicker and more user friendly than stock.

A lot of credit goes to the members here willing to share info and ideas. And a lot of random ideas and theroy I try to incorporate.

 

[Stump Shot]

Well I guess if there were no mystery to it, there would be no fun either. Definitely not as easy as changing a camshaft to get a pretty much known result.

 

[Red97]

Well I guess if there were no mystery to it, there would be no fun either. Definitely not as easy as changing a camshaft to get a pretty much known result.

Try building an echo lol

 

[Stump Shot]

Try building an echo lol

Think I'll broaden myself one horizon at a time.