Stihl 260 muffler mod data, temp, sound level and preformance
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
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Stock muffler opening 0.11 sqr inches
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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
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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
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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
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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
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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
) bundled in your hand... It will form to the irregular shape of the port. Trace on paper, measure area.
