Muffler Mod, how big is too big

[bwalker]

TW, I never set a saw to the arbitrary Max no load numbers provided by the factory. I use a method I learned in my dirt bike days, which I call the cut and feel method. In a nutshell you start out rich and lean the saw out till you achieve max cut speed. You them record the RPM and use that as a target to tune to in the future.
i have found most of my saws impossible to tune by ear, but I have hearing damage from shooting guns and exposure to open stingers exhausts.

 

[manual]

this is only verifying what old timers have said for the longest time.
open up your muffler to 85% of exhaust port. start smaller for it's easier to go larger than reduce in size.

I'm insulted ::hmm3grin2orange: no one has remembered my spaghetti method of determining opening size.

simply fill exhaust port full of spaghetti, then count. reduce number by 15% to come up with size you need.

Don't worry some of us remember.

 

[Erick]

WOW

Man and to think I've been skipping over this thread. Excellent job TW its one thing to drill an arbitrary hole in the muffler and "say" it runs better, its another to document and prove it. Thanks for putting in the time and effort on this one and for posting the results a lot of good info. I always appreciate when people take the time to do things right. Keep up the good work and let us know what you find.

 

[ford832]

Makes me wonder if the muffler has a small effect on the exhaust wave like a pipe does.
Is that little hole we begin with actually keep some of the raw fuel from escaping out the exhaust?
I am sure it is still an EPA thing, but it does make one wonder if muffler design could have an effect on the power curve.

It definately should as the backpressure wave is responsible for keeping the incoming charge from escaping before the piston closes the port-on a dirt bike anyway-not enough backpressure=lost power.I always thought chainsaw mufflers were a little crude compared to a bike.I think all saws need a proper expansion chamber,can and stinger I'll take mine in nickel plate thank you very much
Great thread and great info TW!!!! I'll rep if I can figure it out.

 

[timberwolf]

I realy enjoy this kind of experimentation, to work with ideas and realy get an understanding of how and why things work. Thanks for all the feedback and ideas.

With fuel consumption I am thinking of feeding the fuel from a small graduated bottle rather than the fuel tank, that way it will be easier to keep track of the fuel used.

My question is should I track fuel useage based on operational time or work done. If I mod the muffler and the saw cuts faster but burns more fuel the efficiency might be the same, so measuring fuel consumption over time is flawed, maybe it would be beter to measure how much fuel is needed to make a certain number of cuts in the same sized wood? Though to check fuel consumption at idle it would still need to be measured over time.

 

[timberwolf]

As you mention Ben, a good idea to know at what RPM your saws cut best, I have found this to be helpful, but worth keeping in mind that setting the saw at 15,000 where it cut best one day could be way off another day with a different bar and chain, also changes in temp, weather or elevation could throw off the tuning to a known number approach. If getting down to racing I have even found I can run a hair leaner for 2 cuts in smaller wood than 3 in larger wood.

 

[Industry]

Definitely had to rep you for this. Excellent job, and keep the reports coming. Information is great. I can't wait to start modding saws.

 

[timberwolf]

Did a little work on fuel consumption this afternoon. The results surprised me, will post the results as soon as I clean up the numbers and plug them in.

What do you guys think opening up the muffler does to fuel milage?

 

[hokiebob1]

This is an excellent thread. I work with engines/dyno's every day and jockey the data for a living so this peaks my interest. To me, opening up the port should increase the efficiency of the engine to a point, actually improving "fuel economy" at a given RPM. At some point with larger opening, it may go the other way as efficiency will go down. If tuning by ear, ie. likely higher rpms, fuel economy may stay the same, as any efficiency gained will be traded for higher rpm's.

Thats my guess, but data don't lie.

As for the question on the proper way to measure the fuel economy, it seems to me that the best way would be to measure it against number of cuts, not time. Think of it like gas mileage in your car--you measure in miles, not number of hours until you get there.

thats my $.02, but I'm very interested in the data.

Great Job!

 

[timberwolf]

For the fuel test, I rigged up a 2 oz (60ml) bottle with 3 lines, one for fill, one breather, and one to the carb. For each test I filled it to the top of the lines, so I should have been within 1 or 2 tenths of a ml each time. After each test I refilled the bottle with a graduated syringe. Using the modified saw and square chain.

For the test I put on a muffler opening and tuned the saw by ear, double checked the RPM on the tach, shut it down and refilled. Then cold started and made 5 cuts in 10.5 inch poplar, shutting the saw down as the last cookie fell.

Here is the fuel consumption numbers ml for 5 cuts

17.0 Opening 0.09
16.4 Opening 0.18
15.8 Opening 0.27
15.0 Opening 0.36
14.8 Opening 0.45
14.6 Opening 0.54
14.9 Opening 0.63
16.2 Opening 0.73
17.2 Opening 0.79
17.4 Opening 1.50

Fuel Efficiency acctually improved as the muffler was opened up, but dropped off about the same opening as improvements started to decline on cut times, only with very large openings was fuel consumption worse than stock. Don't know if this would be the same with a stock saw?

By time the saw uses more fuel as the muffler is opened, so the tank gets dry sooner, but the woodpile gets bigger faster. Too a point.

But I think this is just part of the story, It seams there is a lot of LS ajustment made, and a saw spends a lot of time at idle, so need to check that too.

 

[hokiebob1]

Timber, your x axis is in square inches-on your particular saw, how does that relate the exhaust port size....ie. .45 in^2 = 85% exh. opening.

The fuel economy data is interesting, but it raises the question....would you rather have fuel efficiency or quicker cuts. I know what the EPA would say, but would all users want quicker/more powerful cutting?

Cutting faster sounds like the hot setup to me.

 

[timberwolf]

Just go back in the graphs posted earlier and the info is there.

 

[hokiebob1]

Thanks, I found it in the excel sheet.

 

[sperho]

Outstanding timberwolf - great work. I just bought a MS261 Pro and was going to probably open up the muffler after the warranty expires next year. I wouldn't mind gaining a little power, presumably run a little cooler, and yet have a long lasting engine in my saw. Assuming these are my reasoning for a mod, it seems like two 3/8" holes added to the muffler and WOT RPM set to 14k is the ticket? Sounds like a pretty cheap 15% gain in power to me.

 

[Lakeside53]

2x 3/8 is what I've always done.. Timber shows there may be a little more to be gained though, but in the absence of his great data, I played it safe.

If the saw is well broken in, and you like to be close to the edge (I don't 'cos I don't watch them all that closely thoughout the cutting days..) take it up to 14,500..... Then you can give those -026 wannabees (5100) a run for their money... opcorn:

 

[bwalker]

s you mention Ben, a good idea to know at what RPM your saws cut best, I have found this to be helpful, but worth keeping in mind that setting the saw at 15,000 where it cut best one day could be way off another day with a different bar and chain, also changes in temp, weather or elevation could throw off the tuning to a known number approach. If getting down to racing I have even found I can run a hair leaner for 2 cuts in smaller wood than 3 in larger wood.

Given cutting attachments stay the same I have had excellant repeatability using this method. IN fact I have never felt a saw was off using this method and as I am sure your aware I am really picky about how my stuff runs.

 

[Erick]

I've opened the muffler on my MS260 pro to exactly (measured) 90% of the exhaust port and have felt the gains, although I never measured them I always knew they were there, now we have your data, which confirms it.

By time the saw uses more fuel as the muffler is opened, so the tank gets dry sooner, but the woodpile gets bigger faster. Too a point.

This was my personal feelings as well, the saw defiantly runs out of fuel faster but I get the work done faster too with less effort on my part. I always figured the saw got about the same number of cuts for the amount of fuel used, the work just got done faster, and therefore efficiency would be about the same as stock. I was surprised (and pleased) to know that efficiency was actually better.

Thanks again for putting in the time and effort. this is an excellent thread with some excellent information. I'd like to see some more threads like this on AS, non-biased, no "opinion's", just the facts, and you can't argue with the facts. Keep it coming TW (and others)

 

[timberwolf]

Did a little more work. this time measuring the idle fuel consumption, I tried to keep the RPM as close to 3000 as I could, but as the opening got up arround 100% of the port opening the saw becam difficult to keep running at the same speed for the 4 min test. by the time I was up to the full opening the idle needed to be cranked up to nearly 3750 just to keep it stable.

As you can see fuel consumption at idle sky rockets as the muffler is opened up. Jumping from only using about 3ml per min at the smaller openings to over 3 times that amount fully opened.

Second graph is the combined fuel consumption 100% duity cycle (in the cut all the time) 50% duity cycle and 25% duity cycle. These were corrected to reflect the amount of cutting done by the stock opening in 1 min.

This is a very high compression saw with short blowdown, so it should be expected to waste some fuel at low speed.

I did some temperature measurments too, but need to enter them in.

 

[sperho]

Would it be possible to post your spreadsheet for those of us who have Excel?

 

[timberwolf]

I will try, it might work, but I had problems in trying to post an XLS file last time I tried.

No go!

Does not look like AS accepts .xls files for upload.