parrisw
Tree Freak
Sweet thanks. Maybe one day when I feel brave, I'll bore one out.
When you do your tube style muffler mods, do you feel it makes any difference if you extend the tube inside farther? I usually just keep em short.
361 Shootout
- Thread starter timberwolf
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Sweet thanks. Maybe one day when I feel brave, I'll bore one out.
When you do your tube style muffler mods, do you feel it makes any difference if you extend the tube inside farther? I usually just keep em short.
Terry Syd
Addicted to ArboristSite
Brian, I looked at your flow figures for the mufflers and something came to me. I made up a muffler mod that is relatively quiet that utilises the tubes for the mounting screws.
Some guys have taken a grinder through the exhaust port and cut a hole in the tube to use them for exhaust tubes. Unfortunately, since the opening is in direct line with the exhaust port the sonic wave goes straight out the tube and makes the muffler louder.
I chose to drill a small hole in the side of the muffler that I could stick a Dremel tool through and cut a hole on the side of the tube opposite of the exhaust port. The sonic wave can't exit directly out the hole. If the hole on the side of the muffler is kept small enough to just allow the Dremel bit through, the simple patch on the outside is virtually unnoticeable - a stealth muffler mod.
If you ever get some time to play with the stock muffler, it would be informative to see how much that mod increases the flow.
Some guys have taken a grinder through the exhaust port and cut a hole in the tube to use them for exhaust tubes. Unfortunately, since the opening is in direct line with the exhaust port the sonic wave goes straight out the tube and makes the muffler louder.
I chose to drill a small hole in the side of the muffler that I could stick a Dremel tool through and cut a hole on the side of the tube opposite of the exhaust port. The sonic wave can't exit directly out the hole. If the hole on the side of the muffler is kept small enough to just allow the Dremel bit through, the simple patch on the outside is virtually unnoticeable - a stealth muffler mod.
If you ever get some time to play with the stock muffler, it would be informative to see how much that mod increases the flow.
timberwolf
Addicted to ArboristSite
I'll do some more on the stock mufflers some time. There are hundreds of ways to go at them, could be a study all on its own to produce maximum flow with minimum sound levels. I think it is quite likely the baskets in these mufflers help cut some of the sound levels too as the look very much like the insides of a silencer on an exhaust system.
On tube flow I messed with on the flow bench I found up to a point, longer tubes produce more flow per area which would be related to coefficient of discharge. Also, I think they act as a bit of a backflow preventer of sorts blocking some outside air from getting into the muffler and diluting chage at low RPM. The result is needing less LS fuel enrichment to get the same high RPM flow capacity.
On tube flow I messed with on the flow bench I found up to a point, longer tubes produce more flow per area which would be related to coefficient of discharge. Also, I think they act as a bit of a backflow preventer of sorts blocking some outside air from getting into the muffler and diluting chage at low RPM. The result is needing less LS fuel enrichment to get the same high RPM flow capacity.
mtngun
Addicted to ArboristSite
Great data, TW. :yourock:
That's good to know that the screen made no difference. I would never have guessed.
Your data illustrates rapidly diminishing returns beyond a modded single port, just as we have been saying all along.
I can't say enough good about you and the other experimenters who unselfishly share results and particularly the measurements.
You gonna write a book on all this stuff someday, TW ? 'Cuz I would buy it.
timberwolf
Addicted to ArboristSite
I try...
The screen makes no difference as it's area is huge compared to the bottleneck between the screen and the outlet.
I think the dimminishing returns in the case of these two mufflers is the matter of the restriction entering the muffler showing up. Next 361 I have open I will test the flow entering the muffler. When the outlet area is greater than the inlet it makes sense that addition outlet would not give more flow. Some of the difference may have been the difference in the inlets as they were matched to the flanges and the DP muffler was opened just a little more on the inlet side too.
When the muffle is bolted to the cylinder things would change and the coefficient of discharge into the muffler would jump from somewhere just over 0.6 to closer to 0.8 due to improving the shape of the orifice/nozel changing it from a simple hole in the back of the muffler as it was tested to a not to bad nozel formed by a radius edge port and tapered exhaust flange.
The screen makes no difference as it's area is huge compared to the bottleneck between the screen and the outlet.
I think the dimminishing returns in the case of these two mufflers is the matter of the restriction entering the muffler showing up. Next 361 I have open I will test the flow entering the muffler. When the outlet area is greater than the inlet it makes sense that addition outlet would not give more flow. Some of the difference may have been the difference in the inlets as they were matched to the flanges and the DP muffler was opened just a little more on the inlet side too.
When the muffle is bolted to the cylinder things would change and the coefficient of discharge into the muffler would jump from somewhere just over 0.6 to closer to 0.8 due to improving the shape of the orifice/nozel changing it from a simple hole in the back of the muffler as it was tested to a not to bad nozel formed by a radius edge port and tapered exhaust flange.
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Great stuff. I'd rep this whole thread if I could. Solid, reproducible empirical data always makes me happy!
Trigger-Time
Addicted to ArboristSite
Great data, TW. :yourock:
That's good to know that the screen made no difference. I would never have guessed.Your data illustrates rapidly diminishing returns beyond a modded single port, just as we have been saying all along.
I can't say enough good about you and the other experimenters who unselfishly share results and particularly the measurements.
You gonna write a book on all this stuff someday, TW ? 'Cuz I would buy it.
Am with you 110% on TW
About, Stihl's muffler screen, it's so much bigger than the exhaust port
that more flow can get threw screen than the port. I didn't think of that
on my own. Think I have read it in post by TW and Lakeside.
TT
Great work timberwolf!
As long the screen isn't mounted directly to the outlet hole, and at least twice the area, it shouldn't cause a restriction.
The deflectors with the screen between them and the muffler would cause a restriction. But you can just use a larger hole with the screen to make up for it.
As a side question, are you using the MOTA 2 stroke engine simulator? What do you think of it and have you tried any other software?
I was looking around and ran across the trial version of Lotus Engine Simulation, which is restricted to just one cylinder in the trial. It will simulate a 2 stroke so I'm going to try it out.
As long the screen isn't mounted directly to the outlet hole, and at least twice the area, it shouldn't cause a restriction.
The deflectors with the screen between them and the muffler would cause a restriction. But you can just use a larger hole with the screen to make up for it.
As a side question, are you using the MOTA 2 stroke engine simulator? What do you think of it and have you tried any other software?
I was looking around and ran across the trial version of Lotus Engine Simulation, which is restricted to just one cylinder in the trial. It will simulate a 2 stroke so I'm going to try it out.
timberwolf
Addicted to ArboristSite
I am using Mota, some of Blairs older dos stuff and have a few other programs for doing pipes and specific calcs, also have put quite a number of my own calcs into spreadsheets to do things like squish velocity, compression estimations, time area, pipes, flows and such.
I like Mota and have been using it for a few years, it does some things well, others not so well and some not at all. It is a steep and somewhat frustrating learning curve just to get using the software and it takes a lot of time to measure and enter engine data when starting out with a new motor. It is really going to be best for someone who already has a strong understanding of motors and has read some books on 2 strokes, otherwise it could be quite confusing to tackel as it is very much a garbage in garbage out type software.
It is not smooth running software like you get with windows, it is more typical if engineering software, if you don't enter data correctly it won't always tell you, it just quits and the computer needs to be rebooted before it will run a new simulation.
Mota does not do a great job of exportable files for graphs, jpegs ect.
It does not do well at designing a pipe for you but is pretty fair at testing a design you come up with.
It does make good comaprisons of different changes to engine designs, but does not give accurate HP readings without a lot of calibrating it agains known engines. No parametric analysis, each change to a variable requires a whole seperate data file and simulation run.
After I used it quite alot for a year I was still finding usefull features.
To sum it up it is good at testing designs you come up with, but will not help much with teaching how to come up with the design for a good port job.
I like Mota and have been using it for a few years, it does some things well, others not so well and some not at all. It is a steep and somewhat frustrating learning curve just to get using the software and it takes a lot of time to measure and enter engine data when starting out with a new motor. It is really going to be best for someone who already has a strong understanding of motors and has read some books on 2 strokes, otherwise it could be quite confusing to tackel as it is very much a garbage in garbage out type software.
It is not smooth running software like you get with windows, it is more typical if engineering software, if you don't enter data correctly it won't always tell you, it just quits and the computer needs to be rebooted before it will run a new simulation.
Mota does not do a great job of exportable files for graphs, jpegs ect.
It does not do well at designing a pipe for you but is pretty fair at testing a design you come up with.
It does make good comaprisons of different changes to engine designs, but does not give accurate HP readings without a lot of calibrating it agains known engines. No parametric analysis, each change to a variable requires a whole seperate data file and simulation run.
After I used it quite alot for a year I was still finding usefull features.
To sum it up it is good at testing designs you come up with, but will not help much with teaching how to come up with the design for a good port job.
Terry Syd
Addicted to ArboristSite
"On this one I kept the transfers almost stock height by the time the jug gets lowered. And went back about 1mm on the front and 3mm on the rear."
I assume that the increase in the width of the transfers was not simply a flairing of the angle of exit, but an actual increase in the time/area of the ports (and thus the necessary extensive work on the transfer ducts).
You've mentioned before that you have had good results using a transfer time/area slightly below Jenning's figures, I'd really like to know what figure you are working with (I won't tell anyone).
I assume that the increase in the width of the transfers was not simply a flairing of the angle of exit, but an actual increase in the time/area of the ports (and thus the necessary extensive work on the transfer ducts).
You've mentioned before that you have had good results using a transfer time/area slightly below Jenning's figures, I'd really like to know what figure you are working with (I won't tell anyone).
timberwolf
Addicted to ArboristSite
Range I like for transfers on 361type motor is 0.000073 to 0.000093 But it moves around some depending on bore to stroke ratio. I'm right at the top of the range if not a little over on this one.
Another thing I will look at is port velocity. Here are a couple charts @12,000 rpm, the purple line is the one to look at one is the front pair of transfers the other the rear. In general I don't want to exceed 1/3 the speed of sound in transfers or intake otherwise the air starts to compress and decompress more than flow as it should.
Also in the charts it is easy to see there is very little reverse flow in the transfers when they open, a good indication of sufficient blowdown.
Another thing I will look at is port velocity. Here are a couple charts @12,000 rpm, the purple line is the one to look at one is the front pair of transfers the other the rear. In general I don't want to exceed 1/3 the speed of sound in transfers or intake otherwise the air starts to compress and decompress more than flow as it should.
Also in the charts it is easy to see there is very little reverse flow in the transfers when they open, a good indication of sufficient blowdown.
Terry Syd
Addicted to ArboristSite
Good stuff, I've got my transfers at the bottom of your range for 10,000 RPM. I don't think I can go any higher unless I can get some more CC compression.
Looking at the two charts, I can see that the front transfer port is reverse flowing prior to closing. I would have thought that the reverse flowing would have occurred at below peak torque. Do you think that there may have been a positive wave coming in from the exhaust to affect the flow at that port without affecting the rear port?
If so, that opens a whole other can of worms for muffler design.
Looking at the two charts, I can see that the front transfer port is reverse flowing prior to closing. I would have thought that the reverse flowing would have occurred at below peak torque. Do you think that there may have been a positive wave coming in from the exhaust to affect the flow at that port without affecting the rear port?
If so, that opens a whole other can of worms for muffler design.
timberwolf
Addicted to ArboristSite
Quite possible it is, would have to look at some of the other pressure and wave graphs and see where that pressure is coming from.
Terry Syd
Addicted to ArboristSite
Yeah, wouldn't that be a hoot to find out that a positive pressure wave was bouncing back from the front of the muffler - so we put a spacer under the muffler to get the wave to return after the transfers close and we 'pack' the combustion chamber a bit tighter. It ain't a pipe, but I will take what I can get.
parrisw
Tree Freak
There is a tool available, in the auto industry, its a very sensitive pressure sensor used to measure exhaust pulses, you can actually see a leaking exhaust valve with it, by seeing the negative pulse as the engine sucks exhaust back into the engine. Its possible that it could be used to measure the exhaust pulse's/pressure wave's in a saw exhaust? Thought's?
timberwolf
Addicted to ArboristSite
On race engines I have played with that idea and there is something to be gained, far from worth it on a work saw though, also the width of the poweband seems to be very narrow, likely because it is working off a harmonic of a full cycle which would makes sense as the muffler is far shorter than a tuned pipe.
Trigger-Time
Addicted to ArboristSite
This is the one that really fooled me, so 361 filter will flow more than MS660
and MS880 air filter then also. AS 440,460,660 and 880 all use same filter.
TT
timberwolf
Addicted to ArboristSite
Yep, I had to double check it, tested 2 new filters from each and yep the 361 air filter flows more than the HD used on Stihl 440 through 880.
I kind of remember flowing the HD at what I thought was closer to 100 cfm but might have been off base with calcs as it was right back when I was just getting the flow bench working.
I kind of remember flowing the HD at what I thought was closer to 100 cfm but might have been off base with calcs as it was right back when I was just getting the flow bench working.
Trigger-Time
Addicted to ArboristSite
I have kicked around the idea of cutting center out of HD filter.
Then glue two HD together. Install longer stud for filter in my 066 milling saw
and run 2 HD filters. With alum. plate and nut to hold them on saw.
TT
timberwolf
Addicted to ArboristSite
Slick idea!
Likely would not even need to glue them they should seal on them selves.
If you could put a screen over the whole works to help shead the larger stuff it would help too. Filtration for milling is one area where I like the husky design over the stihls as the stihls plug up fast.
Likely would not even need to glue them they should seal on them selves.
If you could put a screen over the whole works to help shead the larger stuff it would help too. Filtration for milling is one area where I like the husky design over the stihls as the stihls plug up fast.
