Another chainsaw dyno...

[Red97]

What muffler was stronger? Pipe or deflector?

Deflector, then pipe. But I didn't swap them.

 

[Terry Syd]

The saw with the most power has the smallest exhaust port.

It would be interesting to discover WHY that was the case. Most people on this forum seem to be enamored with making the exhaust port as wide as possible. Forgetting perhaps the possibility of 'short circuiting' with the transfer ports.

So this is where the dyno comes into it's own. Run the jug and get a reading, then widen the exhaust port to get more time/area and expect an increase in power higher in the powerband - only to go backwards.

 

[Bigmac]

It would be interesting to discover WHY that was the case. Most people on this forum seem to be enamored with making the exhaust port as wide as possible. Forgetting perhaps the possibility of 'short circuiting' with the transfer ports.

So this is where the dyno comes into it's own. Run the jug and get a reading, then widen the exhaust port to get more time/area and expect an increase in power higher in the powerband - only to go backwards.

Agreed! And same with the muffler, the smaller deflected muffler made more than the wide open pipe outlet.

 

[legdelimber]

View attachment 242291
Yellow/green are the same saw from above.

Red/blue is a 3rd hybrid build.

Next week I'll try to get that pile of saws on the dyno.

Interested to hear some thoughts.

Interesting how one saw has the slight bumps in the curve at the 10500~11000 and roughly-ish 11500 to 12000 rpm while the other has the small dip in same regions.

Also makes me curious what you would see in an audio chart. Does the exhaust note get any sharper or fuzzy at any peaks and dips? That and how does the intake "snort" vary across the rev range.

Bah. I'm starting to sound A.D.D. again I guess.

 

[mgr1]

Smaller exhaust port, higher velocity of outgoing exhaust, higher velocity incoming fuel?

Think that a bigger exhaust port is more for a tuned pipe.

 

[Red97]

It would be interesting to discover WHY that was the case. Most people on this forum seem to be enamored with making the exhaust port as wide as possible. Forgetting perhaps the possibility of 'short circuiting' with the transfer ports.

So this is where the dyno comes into it's own. Run the jug and get a reading, then widen the exhaust port to get more time/area and expect an increase in power higher in the powerband - only to go backwards.

2nd most power of any of the hybrids is a 73cc with 8.5hp widest exhaust I've ever run 74% I believe.

Agreed! And same with the muffler, the smaller deflected muffler made more than the wide open pipe outlet.

Maybe the big pipe would have made more on the high up saw? Didn't hardly give time to experiment. Test them, clean an ship them out.

Interesting how one saw has the slight bumps in the curve at the 10500~11000 and roughly-ish 11500 to 12000 rpm while the other has the small dip in same regions.

Also makes me curious what you would see in an audio chart. Does the exhaust note get any sharper or fuzzy at any peaks and dips? That and how does the intake "snort" vary across the rev range.

Bah. I'm starting to sound A.D.D. again I guess.

I am 98% those spikes are the 4 stroke to 2 stroke clean up area. I can hear it during a pull.

Pulling from the top down, the saws are 4 stroking just like being held above the wood. Apply load the little spike is where they clean up.

Red line saw hit really hard, believe the second spike is just a ripple effect from me trying to load the saw down.



Running this load valve is just like fishing....


When a monster hits, you really gotta get on the valve.

Stock saws you can reel in and stall very easy.

 

[drf256]

Looks great Joe. I’m sure you are learning a lot.

 

[jacob j.]

Looks great Joe. I’m sure you are learning a lot.

He's dragging us along with him, and it's an excellent ride.

 

[srcarr52]

I think pipe outlets tend to have a spot in the power curve where they over scavenge. All depends on the length of the pipe.

 

[Billy Currie]

We could try the 145.00 chop fit

I like the results.

 

[Duane(Pa)]

Pretty dang cool that it has such good resolution to see the four stroke, two stroke transition graphically.

 

[TreeLife]

He's dragging us along with him, and it's an excellent ride.

Dragging? Chit, can't drag the willing lol

 

[legdelimber]

Start thinking about the muffler like it's a whistle.

Let's not forget the shapes of holes in musical instruments.
Then go to the math that folks use to figure out standing waves & null points of audio in room installations.

Look at the resonances and do some math on harmonics and half and partial frequencies, etc.
Remember that trick of a resonating string next to the one you were tuning on a guitar? That's a harmonic energy affecting another thing.
Happens in gasses too.
If something has (a) mass or an energy wave/pulse, then it it can be exploited.
oh crap! now we're drifting back into burned & unburned fuel & oil weights and temperatures.

...betcha the effects of mufflers and outlets will start to make more sense though huh.

Same trick behind that goofy chamber in the Dolamr mufflers.
Stuffed up muffler, but it gives a canceling pulse to the exhaust and passes emissions needs.
Now..., maybe go find a way to use it to your advantage?

Read something in a motorcycle magazine in the 70's.
I think it was Morbidelli that pulled some amazing (for the time) peak hp out of their small 2-cycle engines (road racers) with this musical thinking.
Magazine article claimed that they actually pulled a guy in who came from musical instrument design.
Kinda wish I still had some of those old magazines now.

 

[Dieselshawn]

Now that’s a nice dyno.

 

[ferris]

View attachment 242280
The 2 top performing hybrid's today.

Red Hp, Blue Tq

Yellow Hp, Green Tq

So which saws are that?
Red is 73cc???
Yellow is ???

 

[Red97]

So which saws are that?
Red is 73cc???
Yellow is ???

Red 79
Yellow 86

 

[Dieselshawn]

Looking back, I never thought about Land and Sea dynos.

I do know they have them for snowmobiles but never thought about lawn mower size units.

Then would’ve had everything that come with the unit with additional options.

The dyno I built is the almost the same type, just hydraulic oil driven through a gear pump.

Works really well and has been reliable. Just have to hand calculate the numbers to make a graph.

I also like the fact I don’t have to keep looking for logs to cut and human, chain sharpening inconsistencies that can throw numbers out the window.

Also, no mess to clean up.

 

[Red97]

Yep, I was just going to build one, by the time I got everything priced and remotely close to something. It was already expensive.

With no guarantee it would even work.

This land and sea kart dyno showed up. Close enough to my budget to make it work.

When I called they said it would be just over 6k for the dyno setup.

And still have to buy software, and make the test stand.

 

[Dieselshawn]

That’s actually way over my budget what I can afford for the limited work I do.

I do know the dyno can pay itself off over time through dyno use for customers or testing equipment operation.

Dyno Days can make some cash too.

Cutting logs uses up chains, files, time to get the log, transport, clean up etc.

On my dyno, I can disassemble the saw on the machine, change something and put back together without taking the bottom end off the mount.

Makes it fun

 

[Red97]

That’s actually way over my budget what I can afford for the limited work I do.

I do know the dyno can pay itself off over time through dyno use for customers or testing equipment operation.

Dyno Days can make some cash too.

Cutting logs uses up chains, files, time to get the log, transport, clean up etc.

On my dyno, I can disassemble the saw on the machine, change something and put back together without taking the bottom end off the mount.

Makes it fun

Already learning things I would have still been only speculating about without it.

Plan to do a bunch of runs this week.