MillerModSaws
USE2COULDBESPONSER!
Agreed but when removed it's just like an old saw before strato.
MillerModSaws and the PS-7910
- Thread starter MillerModSaws
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Paragon Builder
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What's its purpose?
Mastermind
Work Saw Specialist
I'm not 100% sure.....but I think it gets really hot, and burns off hydrocarbons in the exhaust.
A lot of the work in this build is getting rid of it though.
My guess is its helping keep the fresh charge in the cylinder and not letting it out the sneak out exhaust. look at it like a tuned pipe and you can see what I'm talking about.
MillerModSaws
USE2COULDBESPONSER!
Welcome back. Hope all is well down in your neck of the woods.
Mastermind
Work Saw Specialist
I've thought about that too.....but just ain't buying it. I really think it's about emissions....
Mastermind
Work Saw Specialist
We survived......and the shop is finally warmed back up.
Tractorsaw1
ArboristSite Guru
Can these 7910's do anything a 7900 can't? Sorry I don't know enough about them other than you can't get them as cheap as the 7900's were. But this thread makes me want to get a 7900 to open up.
Nice work Carl
Nice work Carl
Its a Helmholtz chamber, so I cant see it just being used to get hot and burn off emissions.
Think of it this way.
During initial blowdown a portion of the exhaust is going out the hole in the bottom of the resonant chamber, the remaining exhaust that cant make it out the port is filling up the lower pressure "closed" portion of the chamber. Blow down continues, the closed chamber reaches pressure equilibrium and now all flow is out the port in the chamber .
Ideally the pressure in the chamber (at the exhaust port) remains equal or slightly lower to the pressure in the cylinder while the transfers and exhaust port are closing while the closed portion is bleeding off the pressure it gained during blowdown
In some two-stroke engines, a Helmholtz resonator is used to remove the need for a reed valve. A similar effect is also used in the exhaust system of most two-stroke engines, using a reflected pressure pulse to supercharge the cylinder (see Kadenacy effect.) http://en.wikipedia.org/wiki/Helmholtz_resonance
Mastermind
Work Saw Specialist
Good stuff........
It's a good day........cause I learned something new.
It's a good day........cause I learned something new.
MillerModSaws
USE2COULDBESPONSER!
X2. I'm going to haft to reaserch this helm Holtz chamber. But if it's acting like a piped saw. Would that explain the shorter blowdown in the 7910 over the 7900? Good thread guys keep it up!Good stuff........
It's a good day........cause I learned something new.
It is just a fancy way of stuffing the exhaust up so that fresh mix doesnt escape out the exhaust was always my thought of what it did just looking at it but @jar944 knows more than me and after reading what a Helmholtz chamber was i am rethinking how it works and its effects
In some two-stroke engines, a Helmholtz resonator is used to remove the need for a reed valve. A similar effect is also used in the exhaust system of most two-stroke engines, using a reflected pressure pulse to supercharge the cylinder (see Kadenacy effect.) http://en.wikipedia.org/wiki/Helmholtz_resonance
ha, Nice that pic would have saved me some typing.
gritz
ArboristSite Guru
Seems like there needs to be some tinkering with this SLR thing? I would be curious to see two things. The first is the exact difference between running a stock saw with or without it (leaving the opening in the muffler outlet the same size) , the second is running a ported saw with or without it. Then if it helps a stock saw, but hinders a ported saw, it would be nice to see if the SLR and exhaust outlet were enlarged to accommodate more airflow on a ported saw to see if it helped or hindered the saw.
Mastermind
Work Saw Specialist
So.......is this a performance enhancement, or just a emissions device? Is the volume of the chamber sized for a stock saw? If so, will it be too small for the output after mods?
MillerModSaws
USE2COULDBESPONSER!
I have hacked this SLR unit up already but early I was asked how much will it hold. If you hold it with the chamber down and fill it till it hits the exhaust hole it holds 69 ml. So that would be 69cc.
strictly emissions/fuel economy. Though correctly sized it shouldn't hinder performance.
Its not functioning like a performance pipe. Its just there to "shut the door" on the exhaust port.
honestly i cant tell the difference when they are removed from a stock saw running a 20" bar but the PC-7414 has the same thing and removing it plus adding a second outlet to the muffler really wakes those up when cutting arbor deep in concrete
Mastermind
Work Saw Specialist
LegDeLimber
Addicted to ArboristSite
I see that some of you guys are,
finally,
waking up to that pulse chamber and how it works.
Stopping the flow out of the exhaust, is stopping the flow, is stopping the flow....
you won't likely be able to tune for an extraction,
But,
You can use that thing to stop the charge loss from a slightly wilder porting idea.
I'd say you might find a narrow spot, oh maybe 60~100 rpms wide
that the chamber would
expel a pressure wave that you could exploit.
tangential thought?
Grab a copy of some software for figuring speaker cabinets, plus one for room acoustics
and go from there.
Have fun fellers!!
going wild on the thinking for a second here:
Hmm, maybe open the top of the exhaust a pinch earlier and see if the gas rushing out
carries enough inertia to give slight pull on the incoming charge.
Now use that chamber to staunch the flow, when it kicks back the stallout/stoppage of flow or is it a positive wave with reversed/back flow?
Again though this will only hit on a narrow assed frequencey band, that might be exploited.
Nasty, skinny spike in the power curve though.
It obviously works well enough to keep the unburned charge losses in check.
Keep asking yourselves
how !!
oh and don't forget about boost bottles concepts, just move it over to the exhaust stream thoughts.
I.E. http://www.superstreetonline.com/how-to/engine/modp-1102-motordyne-tuning-test-pipes/
finally,
waking up to that pulse chamber and how it works.
Stopping the flow out of the exhaust, is stopping the flow, is stopping the flow....
you won't likely be able to tune for an extraction,
But,
You can use that thing to stop the charge loss from a slightly wilder porting idea.
I'd say you might find a narrow spot, oh maybe 60~100 rpms wide
that the chamber would
expel a pressure wave that you could exploit.
tangential thought?
Grab a copy of some software for figuring speaker cabinets, plus one for room acoustics
and go from there.
Have fun fellers!!
going wild on the thinking for a second here:
Hmm, maybe open the top of the exhaust a pinch earlier and see if the gas rushing out
carries enough inertia to give slight pull on the incoming charge.
Now use that chamber to staunch the flow, when it kicks back the stallout/stoppage of flow or is it a positive wave with reversed/back flow?
Again though this will only hit on a narrow assed frequencey band, that might be exploited.
Nasty, skinny spike in the power curve though.
It obviously works well enough to keep the unburned charge losses in check.
Keep asking yourselves
how !!
oh and don't forget about boost bottles concepts, just move it over to the exhaust stream thoughts.
I.E. http://www.superstreetonline.com/how-to/engine/modp-1102-motordyne-tuning-test-pipes/
