Torque, RPMs, Porting...My Philosophy

[Termite]

" Neither one should eclipse the other. It takes both to make a fast saw. IMHO, if I haven't figured out how to get both out of a saw, I'm not happy and don't feel like I've mastered that model yet. If the saw doesn't make more RPMs than stock at the same load, then it's not going to cut any faster. If the saw is making RPMs, but only at a lower load, then torque is insufficient. I demand both."

So Brad which saws have you mastered and which ones are still a challenge? Please be specific, it's more interesting

 

[HuskStihl]

So, this is opening up a whole other can of worms, but this is why I think a good dyno would be so helpful. If your knew your favorite ported saw made max power at 11K and max torque at 9k, it would be so much more predictable to know what was going to make you happy with a different ported model. It would also be interesting to see what makes a subjectively "torquey" saw feel that way. Does it have more torque, or just have the torque in a different point in the power band? Not trying to derail

 

[Haywire Haywood]

To me, the logical way to making a faster cut is faster chain speed (all else being equal). To achieve faster chain speed under load, seems like the peak torque of the saw needs to be moved higher in the rpm range.

 

[RedneckChainsawRepair]

Back when I was into such stuff. I dont give a crap about what rpm's it reached out of the wood. Big fing deal. It is those rpm's it HOLDS IN THE CUT that count IMO.

I seen many of ported saws by folks when they hit the wood would drop 3k to 5k from their out of wood rpm's.

 

[MustangMike]

Brad, regarding your "deep in the woods logger" example, it would be interesting to test if the ported saw does more work with the same amount gas, rather than just noting that it goes through gas faster.

If the logger can do the same amount of work with the same amount of gas, but in less time, that should put a smile on his face.

Have a ported saw and a non ported saw, each one cuts X number of rounds through similar wood, then shut the saws off and measure the remaining fuel (also note the time savings for the ported saw). I know the test seems like a bit of a pain, but it would provide some real world useful information.

 

[treeslayer2003]

LMAO.........it will put a smile on his face if the saw cuts its azz off in the wood he is cutting........regaurdless of fuel. as long as its not silly, like every two minutes its out.

 

[chadihman]

Back when I was into such stuff. I dont give a crap about what rpm's it reached out of the wood. Big fing deal. It is those rpm's it HOLDS IN THE CUT that count IMO.

I seen many of ported saws by folks when they hit the wood would drop 3k to 5k from their out of wood rpm's.

I'm no pro here but the saws I tested with high unloaded rpm have a higher torque rating in the higher rpm range.the high rpm is probably from the increased torque that can overcome the drag on the saw and run faster as most stock saws have a very low torque # above 10,000 rpms. Now I have seen saws that have an impressive high rpm torque # giving them max hp at much higher rpm than a stock saw but the torque doesn't hang in there. A saw with more torque at higher rpms will cut the fastest if the saw runs in that rpm range. Lots of those saws fall on there face if the dogs are used pulling the saw into a rpm range that doesn't have the torque to support it. I can post a couple graphs later if you want. I have a stock 361 vs ported 361, a stock 460 vs ported 460 and a stock 261cm vs a ported 261cm coming up.

 

[chadihman]

To me, the logical way to making a faster cut is faster chain speed (all else being equal). To achieve faster chain speed under load, seems like the peak torque of the saw needs to be moved higher in the rpm range.

Yep but the saw also needs the torque to remain there for a couple thousand rpms to keep it from falling on it's face if it dips bellow the sweet spot.

 

[Philip Wheelock]

Prefer a broad torque band in a ported work saw: make good torque @ lower rpm & maintain right on up through extended high rpm (under load). Just a guess: max HP @ 10.5-11.0K rpm rather than 9.5K rpm = faster chain speed. Run synthetic oil @ 32:1.

 

[chadihman]

Prefer a broad torque band in a ported work saw: make good torque @ lower rpm & maintain right on up through extended high rpm (under load). Just a guess: max HP @ 10.5-11.0K rpm rather than 9.5K rpm = faster chain speed. Run synthetic oil @ 32:1.

Porting usually moves the torque curve to another level.

 

[Haywire Haywood]

Higher unloaded rpm may be incidental to getting the torque where you want it, it's not a goal in itself.

 

[blsnelling]

Higher unloaded rpm may be incidental to getting the torque where you want it, it's not a goal in itself.

Part of the purpose of this discussion is to change the focus from torque to power. Torque is only half of the equation. My goal is to broaden the torque curve and move max HP to the right.

 

[tlandrum]

squirrel >>>>>>>>>>>>>>>>>>>>>>>>>>>

 

[blsnelling]

squirrel >>>>>>>>>>>>>>>>>>>>>>>>>>>

Just a little TLTR? Yeah, I know!

 

[pastryguyhawaii]

I'm just wondering what kind of wood that is, Brad? Looks like it will make some nice tables.

 

[blsnelling]

We don't know, but she is making takes of those slabs.

 

[farrell]

Just judging from the bark and the look of tree and wood looks like an old sugar maple

 

[Chris-PA]

OK, improper use of units and quantities leads to confusion and a lack of clarity.

Torque and horsepower are not unrelated quantities. Horsepower = Torque X rpm (times a scale factor, but forget that). I can make a couple of hundred ft-lbs at zero rpm, but that doesn't represent any power output because any torque X zero = zero. What matters here is power - the torque value isn't relevant because it is part of the power. Power is what gets the work done.

Because the cutter spacing is fixed, the load is proportional to the number of cutters passing a point per unit time. So if you want a 10% higher chain speed then you have roughly a 10% higher load. That means a 10% higher chain speed requires 10% more hp at a 10% higher rpm. However, if you manage to push on it, increase the load and drop the speed back down, then you won't want to have lost any power down there or it will stall (bog).

It is still just a question of power at rpm, not of torque.

 

[RedneckChainsawRepair]

Somebody mistakenly thought I was talking stock v/s ported saws. I was talking ported v/s other ported saws.

Just be careful who you choose and get the saw ported right for your needs.

 

[Mastermind]

Ain't we beat this into the ground already?

Just build a saw that nets good solid, and repeatable gains. Make it last, and you'll have happy customers.

What's the big deal?

It ain't rocket surgery.