Another chainsaw dyno...

[Red97]

Wasn’t 100% sure this new setup was the same.



Carry on, nothing to see here.

Real similar. Lower rpm higher tq, high rpm lower tq.

Runs are done the same way, high rpm then apply the load.

 

[dall]

bump

 

[Dub11]

Hey Joe Red97 have any big Merican mag saws been run on that dyno?

 

[Red97]

Hey Joe Red97 have any big Merican mag saws been run on that dyno?

None on the new system. I'm sure some will roll in once I get back to run it...

 

[Dub11]

None on the new system. I'm sure some will roll in once I get back to run it...

What about the old?

 

[Red97]

What about the old?

Think the oly oldie was a super pro mac 60 or something like that.

 

[Nutball]

I'd like to see the difference between a normal piston and a dished one. Is the loss in compression made up for by a higher volume of fuel/air mix? Lower compression saws are supposed to rev higher right? So, maybe by using an extra thick aftermarket piston, stock compression could be maintained, but with a much larger volume of mix. And an exhaust port could be lowered, and squish set without having super high compression.

 

[mgr1]

You can't get more air fuel in it due displacement without super- or turbocharging it.

 

[Duane(Pa)]

Nutball, you are right about compression. There is a point of diminishing returns. It takes more energy to make it happen than it yields on the power stroke. Extra heat becomes an issue as well.

 

[wcorey]

In my limited porting experience, I've yet to have a saw held back in rpm by compression (by work saw standards anyway) and I typically set them up well north of 200psi.
What I do see is that holding a tune becomes an issue at some point.
I have an aggressively ported 394 that turns out was running at 285psi+ and it was driving me crazy leaning out in the cut, lack of rpm was not an issue.
Didn't want to change port timing so I enlarged the combustion chamber to bring it down some and that seemed to suck some of the life out of it, relatively speaking.

 

[TreeLife]

In my limited porting experience, I've yet to have a saw held back in rpm by compression (by work saw standards anyway) and I typically set them up well north of 200psi.
What I do see is that holding a tune becomes an issue at some point.
I have an aggressively ported 394 that turns out was running at 285psi+ and it was driving me crazy leaning out in the cut, lack of rpm was not an issue.
Didn't want to change port timing so I enlarged the combustion chamber to bring it down some and that seemed to suck some of the life out of it, relatively speaking.

Heat from excessive compression is what caused that lean condition, likely. The whole thing with any engine is this: its an art of compromise.

 

[wcorey]

Heat from excessive compression is what caused that lean condition, likely. The whole thing with any engine is this: its an art of compromise.

I entirely agree...

 

[TreeLife]

I built engines for hot rods, LS engines for boost, various engines for fast boats. Each one had different requirements/jobs and they needed to be tailored to as such. A chainsaw engine is no different, but achieving the goal is. Port timing and duration, ignition curve/advance, compression and case capacity all play a role in the powerband of a saw. The interesting part about piston ported engines is that what may work for one will be detrimental to the other. Lots of fun in the sun for sure....

 

[MustangMike]

There may be other reasons for it, and I never measured the compression, but on some MS 660 clones, raising the exhaust sure seemed to increase RPMs with that engine.

I've been told they behave differently than a 440/460 because of the longer stroke.

Truth be known I also widened the Intake a bit at the same time, so multiple things may have contributed.

I agree with both of you that everything has to be in sync.

 

[RI Chevy]

They gotta be all in unison like a concert orchestra. [emoji106]
The whole package has to work together as 1.

 

[Moparmyway]

In my limited porting experience, I've yet to have a saw held back in rpm by compression (by work saw standards anyway) and I typically set them up well north of 200psi.
What I do see is that holding a tune becomes an issue at some point.
I have an aggressively ported 394 that turns out was running at 285psi+ and it was driving me crazy leaning out in the cut, lack of rpm was not an issue.
Didn't want to change port timing so I enlarged the combustion chamber to bring it down some and that seemed to suck some of the life out of it, relatively speaking.

I went from this
To this
Just so I could start it myself

The saw didn’t lose any grunt, didn’t gain any either

 

[TreeLife]

I went from thisView attachment 279392View attachment 279395
To thisView attachment 279393View attachment 279394
Just so I could start it myself

The saw didn’t lose any grunt, didn’t gain any either

Did you make a bevel in the chamber to remove material? Hard for my poopie eyes to see.

 

[sawmikaze]

"Worksaw" north of 200 psi ? No franks.

 

[Nutball]

Maybe if it was Diesel

 

[drf256]

Depends on the saw, but I have multiple Worksaws over 200 psi. As for rpm, I guess one would say safe RPM-not leaned out.

The smaller bore saws have more relative cooling area/bore ratio than the large bores.

Autotune helps one out too, it can overcome the leaning out from too much compression issue by compensating real time.

That’s part of why AT saws will usually beat a manual tune saw, you get the best of both worlds in some way-and it’s safe too. I’ve had to drill the nozzle in some AT saws so that they could compensate and the results were rewarding. For clarification, the jets in Stihl MT saws are in the nozzle side(s).