Stihl 260 muffler mod data, temp, sound level and preformance

[timberwolf]

Here is the data I measured during a muffler modification on my 260.

Saw is was new 3-4 tanks of gas, sharp .325 Stihl RS chain on a 16" bar.

Tempratures were measured with a digital lazer spot infared sensor. measuements were taken from the hottest area on the front of the muffler cover, and the hottest exposed area of the head which seemed to be just below the cooling fins on the bar side. Outside air temperature 5 degrees C.

Sound levels were measured using a calibrated digital sound meter, peak measurments were taken at 10 feet directly in front of the saw with both the saw and meter 3' above the ground (open field).

Cut times were 3 cut averages measured by stop watch on a 12" dry spruce.


The muffler modification entailed 5 steps.

1 stock
2 stock muffler redrill existing outlet to 7/16 and add one 7/16 hole
3 add one more 7/16 hole
4 join 3 holes and square opening to 7/16 x 1.5 inch plus file back and open deflector angle.
5 match exaust port to muffler

The test consisted of the folowing steps

1 measure temp with saw cold roughly 7 degrees C
2 start and idle saw for 2 min monitor temp until stable
3 measure idle sound level
4 cycle saw to full RPM 5 times and record max sound and rpm
5 cycle saw between idle and full rpm for 1 min and measure temp
6 cut 3 disks and measure temp
7 allow saw to cool befor next test

AND HERE IS WHAT I FOUND
-----------------------------------

Stock muffler opening 0.11 sqr inches
---------------------------

RPM 13450
Idle sound level 80.2 db
Max sound level 97.1 db
Idle temp muffler 64 C
Idle temp head 60 C
Cycle test temp muffler 119C
Cycle test temp head 68C
3 cut test temp muffler 183C
3 cut test temp head 105C
3 cut test time 8.5 sec


Muffler with two 7/16 openings total 0. 30 sqr inch
---------------------------------------

RPM 13650 +1.5%
Idle sound level 84.9 db +5.9%
Max sound level 99.5 db +2.8%
Idle temp muffler 62 C -3.2%
Idle temp head 58 C -3.4%
Cycle test temp muffler 89C -33.7%
Cycle test temp head 62C -9.7%
3 cut test temp muffler 164C -11.6%
3 cut test temp head 96C -9.4%
3 cut test time 8.0 sec -6.3%

Muffler with three 7/16 openings total 0.45 sqr inches
-----------------------------------------

RPM 13750 +2.2%
Idle sound level 87.1 db +8.7%
Max sound level 101.8 db +4.8%
Idle temp muffler 56 C -14.3%
Idle temp head 55 C -16.4%
Cycle test temp muffler 88C -35.2%
Cycle test temp head 62C -9.7%
3 cut test temp muffler 147C -24.5%
3 cut test temp head 105C -12.9%
3 cut test time 7.6 sec -11.8%

Muffler with one 7/16 x 1.5 inch opening total 0.66 sqr inches
--------------------------------------------------

RPM 14000* +4.1%
Idle sound level 89.9 db +12.1%
Max sound level 103.0 db +6.1%
Idle temp muffler 54 C -18.6%
Idle temp head 52 C -15.4%
Cycle test temp muffler 82C -45.2%
Cycle test temp head 61C -11.5%
3 cut test temp muffler 143C -28.0%
3 cut test temp head 85C -23.6%
3 cut test time 6.9 sec -24.6%

* mixture richer by a hair RPM = 14100 before adjustment

Exaust port matched and smoothed
---------------------------------------------

RPM 14050 +4.4%
Idle sound level 89.9 db +12.1% NC
Max sound level 103.0 db +6.1% NC
Idle temp muffler 54 C -18.6% NC
Idle temp head 51 C -17.6%
Cycle test temp muffler 82C -45.2% NC
Cycle test temp head 61C -11.5% NC
3 cut test temp muffler 143C -28.0% NC
3 cut test temp head 83C -26.5%
3 cut test time 6.7 sec -26.8%


Other Notes

My cutting tequnique may have improved over the tests, however I was cutting disks off towards the larger end of the log during the last few tests, so it probably equals out.

The air temprature was cool for the tests, the engine tempratue factors may well be more pronounced if the same tests were done during hot weather.

Even though the sound level data shows an increase of 12% idle and 6% maximum the real change in much greated due to the logarithimic nature of the db scale, the precieved change of a 10 db increase as in the saw idle measurments would be that the sound level has doubled.

Allthough the mixture seemed to be good at 14000 rpm I richened it to achieve 13800 when I was finished.

gains don't seem to be falling off too fast so I will likely open up the muffler a wee bit more in the future.

Data tables don't post well, I think I'l make it a text file and attach it next time.

Wife didn't think much of me spending most of the day making the chain saw louder! Just wait til I finish the 066. lol

Timberwolf

 

[treeclimber165]

WOW!

Thanks for putting this together. This the type of info most typical saw owners need to see. I appreciate how you strived to make the info as accurate as possible. Even with any standard of variance, your results show ABSOLUTE proof that muffler mods reduce head and muffler temps and allow the saw to perform better with less resistance. Heck, I gotta bookmark this thread!


I rated this thread a '5'. When it gets enough votes, the rating will show up.

 

[chainsawworld]

timberwolf,
do you or did you ever work for me? sounds like the crazy sick stuff we do here. marty

 

[Crofter]

--Faster AND Cooler--

This is what we have been hearing about muffler modifications on the newer restricted saws. 25%or so faster and seem to run cooler. It is nice to see actual measured cylinder an muffler temperatures to support it. So what if you do have to buy your wife a pair of ear muffs too!

Crofter

 

[tundraotto]

well done Timberwolf!!! Well performed test. I am glad to see some empirical data about the temperatures especially. Your time spent is well appreciated!! Just shows how we have been screwed by the EPA....

PS. could you do a test with your Raytek regarding fuel mix, ie. 32:1 head temp vs. 50:1 head temp??? That would be another interesting one.

 

[rahtreelimbs]

Timberwolf!!!

Thanks for taking the time to do these tests. This is as Tim said concrete proof. The mufflers that I modified made the saws feel stronger as I never had any solid proof.

 

[timberwolf]

Yes that would be interesting to check mix VS head temp.
I should have mentioned in my original post that the mix was 40:1 with Stihl oil for the muffler tests, I guess it could make a differnce.


It is a bit dark out now, and with that modified muffler I'd just get busted by the noise police aka "WIFE"

I will give it a try tomorow

Timberwolf

 

[bwalker]

Good job. Its good to see someone finnaly prove and doccument what many have thought for so long=Epa mufflers are cooking our saws and killing power. As afar as the mixture thing goes. the only thing you will have to watch out for is keeping the adjustments equal. IE more oil will lean it out slightly so the mixture screws must be a bit richer, in practice this amount is very slight, but it could still make a differance.

 

[stihltech]

excellent

Nice job. Real world testing.

 

[Tom Dunlap]

On Thursday I called my brother in Dallas and asked him to send me his sound meter. As i start to tweak mufflers I want to collect sound ratings. I don't have a temp meter though. I plan on collecting the dB changes and cutting time changes. The nursery has a pile of old 6x6 timbers for me to cut up. They should be pretty uniform.

Thanks for taking the time to collect and post this valuable information.

Tom

 

[Acer]

This is really good work, and takes the idea of exhaust mods beyond anecdote.

I noticed your RPM increased in line with opening area, so anyone attempting these mods ought to retune their saw to avoid engine damage through over-revving (max. engine speed on an 026 is quoted as 14,000 rpm in the manual).

Just one thing: I think the perceived noise increase is more than you think. You're right about the dB scale being logarithmic, but a 3dB increase represents a doubling in sound pressure level.

 

[Kneejerk Bombas]

The test is great.
One question I have is about the RPMs and cut speed. Shouldn't you have adjusted the carb to the same factory reccomended setting each time?
I say this because just leaning out the carb to increase RPMs would decrease cut times, to some extent, wouldn't it?

 

[camel]

That is why i love this site...

Verry Good Job !!!!

 

[chainsawworld]

timberwolf,
i'm glad you proformed your tests and got a great welcome. i recall posting some information close to what you did and it did not go over as well. i heard things like a hand held instrument (tach or thermometer) can not hold a true reading. lots of people enjoyed what i posted but a few fought my results. i also supplied timed cutting results. thank you; marty

 

[tundraotto]

when was this marty? I belive by the description that timberwolf used a Raytek infrared thermometer that is the industry standard and record the temp with a .1 degree accuracy - approx between 50 -1300 degrees - is that what you used? tach is great to use, but where your test conducted in specified conditions like these were? ie. same saw, same beginning temp, same log, same sawyer, same chain, same day, etc.??? please post a link.

 

[timberwolf]

One question I have is about the RPMs and cut speed. Shouldn't you have adjusted the carb to the same factory reccomended setting each time?

I can see your point but,

I intentionaly avoided adjusting the mixture, it would have thrown another wild card in, I only adjusted it when the saw did not break between 2 and 4 cycle at full unloaded throtle.

Now wether the saw was increasing RPM through leaning of the mixture due to increased flow and improved scavenging or wether it was less resistance to exaust flow (another question). I would think most likely a combination of factors.

Timberwolf

 

[timberwolf]

Just one thing: I think the perceived noise increase is more than you think. You're right about the dB scale being logarithmic, but a 3dB increase represents a doubling in sound pressure level.

Actualy I had to double check this in a text book befor my original post, 3db is a doubling is sound preasure level, but our ears don't follow a liniar responce to the SPL. according to The text I have concerning sound systems a 10 db gain is what the average person precieves to be a doubling of apparent sound level.

If a 3 db gain was precieved as twice as loud then the 9-10 db increase would be precieved as 8 times as loud. The saw was louder but not that much louder.


This sure builds a case for good hearing protection, proper ear muffs give a typical db atenuation of -25db to -30db. if the saw is 103 db at 10 feet it would be more like 110 to 115 for the opperator. With established so called safe sound levels being around 85db ear muffs would provide only marginal protection. This is likely part of the rational to restrict mufflers to ensure that standard hearing protection brings sound levels within ocupational health and safety guidelines.

Timberwolf

 

[chainsawworld]

i'll go back through the threads. it was with a 372xp. the muffler was walkerized,digtial tach and laser thermo. the cants were 8x8, same day, same carb settings and on and on!!!!!! marty

 

[tundraotto]

well....what did you find Marty?

 

[Acer]

Originally posted by timberwolf
Actualy I had to double check this in a text book befor my original post, 3db is a doubling is sound preasure level, but our ears don't follow a liniar responce to the SPL. according to The text I have concerning sound systems a 10 db gain is what the average person precieves to be a doubling of apparent sound level.

I learn something every day. In a previous job, I used to take rough sound surveys in factories, just to see if a more in depth survey was needed. We were more interested in sound pressure level, as this does the damage. Then, the acceptable dose was the equivalent of 90dB over an 8 hour period (it has dropped to 85 dB now, I believe)- any higher would result in hearing damage. So, an operator running a saw with no hearing protection and experiencing 114dB, say, would receive their dose in just under 2 minutes!!