Muffler Mod, how big is too big

[timberwolf]

I did a little testing on opening up a muffler on an 026, this was posted about the web, but did not generate too much interest, though maybe it could be helpful.

Basicaly what I did was weld up a blank muffler cover for an 026 with a front plate that could be easily modified with different opening sizes.

Each time I tried a new opening the saw was tuned by ear to the edge of 2 stroking and then I made several cuts in a 10 inch poplar taking the best time.

Saw is bone stock except for a improved 260 air filter.

What I found was from a stock opening to 120% of the exhaust port size there was about a 20% improvement in cut times. Going further up to 400% of the port area continues to give small gains totaling another 5%.

I did also find that maintaining a good idle became problematic over 190% of the port area.

Here are a few pics and graphsopcorn:

 

[timberwolf]

Graphs

Here is the data visualized

 

[oldsaw]

Nice work. Good job keeping records on your progress. That's what's missing when mods are done. Easy to infer that louder is better, but time is what tells the truth.

Mark

 

[timberwolf]

There is more I want to do with this, but it all takes time.

How does a tube stack up to the round hole of the same diamiter?

Muffler temp, head temp and fuel consumption?

Also have two modified 026s, I would like to repeat the test with those saws to see if there are any differences? One saw is ported low for torque, the other ported very high realy designed to run on alky and pipe.

 

[bwalker]

Good job, TW.
The only thing I would have done different would have been to use a tach vs. tuning by ear, which I find is notoriously inaccurate with some saws. I might also add a companion test in larger wood so as to ascertain the effect of ever increasing outlet sizes on torque.
The intent of my comments is not to pizz in your cheerios, but to stimulate discussion.

 

[timberwolf]

I did use a tach to measure the setting as I could best determine by ear, infact I did a similar test a couple years ago and set by tach for the same RPM each time., the problem is that mixture then is set way too rich too keep the RPM down once the muffle is opened up and the saw wants to turn some RPM. This is also why I enlarged the filter area before I started, the old style 026 filter is very restrictive and is on the edge of being a problem with the stock meffler opening.

Once I set by ear I did a test cut then double checked it by richening a little and re cutting then leaning a little and re cutting, so I realy was hunting for the best cut time each time. With the first couple increases to the muffler opening the gains were pretty clear and it was easy to tune and see that the saw was tuned for the best cut time. However as the muffler opening became larger tuning became a little more dificult and the gains harder to see from one test to the next.

It is very hard for me to test and measure 1 or 2 % gains from one cut to the next, too easy for operator error or changes in the wood to skew the results. But I did my best to avoid this as much as possible.

 

[bwalker]

Sounds like you where on top of it then.
Did you get the feeling that torque fell as outlet size increased beyond a certain point?

 

[timberwolf]

No, torque stayed good.

Goin in I though there would be a point where it might start to miss in the cut, but didnt see that.

One surprise was, as I started to open the muffler up I needed to do more increase on the LS and actually needed to lean the HS a little. I guess the LS was over contributing. As the increased demand at HS was not nearly what the increased fuel demand was at LS, however the fuel trrough the LS can make up a good 1/4 to 1/3 of the total fuel flow at full RPM.

The major issue was having a decent idle above 190 % of the exhaust port the idle started getting a little touchy and I needed to bring the idle RPM up to keep the saw from either loading up at idle and stumbling on spool up or being too lean at low speed and reving on after the throttle had been dropped.

 

[precaud]

Great info, thanks. I'm guessing this data can be scaled proportionally for other cc's with similar results, yes?

 

[timberwolf]

In general maybe, but each saw has it's own muffler and port dimentions, port timing and RPM, so I would expect to see variation from one saw to the next.

Some saws are much more choked down to start with, so would show beter gains, some of the older saws were more open and less would be had by opening up the muffler.

I opened up a Cat muffler on a 359 and the gain was closer to 35-40% on the cut times.

Chain can play a role, if the chain is dull and your pushing for all your worth a muffler mod and some extra HP won't make any difference.

 

[Jaxx]

Good info. The graphs were great. Thanks for sharing your work.

Jaxx

 

[precaud]

Just curious, what's the diameter of the 026 piston?

 

[chowdozer]

Good job, TW.
The intent of my comments is not to pizz in your cheerios, but to stimulate discussion.

Wow!!! You're a changed man! What happened?

 

[RiverRat2]

Dang it bwalker

Good job, TW.
The only thing I would have done different would have been to use a tach vs. tuning by ear, which I find is notoriously inaccurate with some saws. I might also add a companion test in larger wood so as to ascertain the effect of ever increasing outlet sizes on torque.
The intent of my comments is not to pizz in your cheerios, but to stimulate discussion.

Don't you remember desiring torque in a saw dont have nothing to do with performance,,,, especially if you go up in log size???????
Just kidding,,,,,, I think you are right on target with your comment and question Tried to Rep TW but it busted my chops, guess you are it if it will, it wouldnt let me,,on either one of ya
Interesting Thread,,,,, More data is good!!!!!!!!!!!!

 

[RiverRat2]

Sounds like you where on top of it then.
Did you get the feeling that torque fell as outlet size increased beyond a certain point?

I would have thought the samething about the T falling off???? :monkey: :computer:

 

[bwalker]

Wow!!! You're a changed man! What happened?

The differance is TW is not a hack.

 

[Bowtie]

Timberwolf, If I may ask, what carb you using on your 026?

 

[Lakeside53]

Great work! It seems to validate that 125% of exhaust port area is a good rule of thumb for decent results.

 

[timberwolf]

I have a few 026 carbs, with out pulling it appart I would guess it is a 426, not sure though.

I'm still a hack Ben, maybe just a refined one.

 

[Lakeside53]

Just curious, what's the diameter of the 026 piston?

44mm