Read Gum dust and Stihl HD Filters

[Karl Robbers]

Does any one know how much air is getting sucked into a saw / min or what ever,im thinking its going to be a lot.

Assuming 100% volumetric efficiency, (which you won't get but it is a nice number to work with), multiply your displacement by your engine rpm's which will give you cc's per minute, now divide this by 1000 to give you litres per minute or divide by 28.317 to give CFM, (cubic feet per minute).
This is for a 2 stroke engine, for a four stroke divide final results by 2.
eg. A 95cc 2 stroke saw at 12500 rpm would draw 1187.5 LPM of air, or 41.94cfm.

 

[MCW]

Assuming 100% volumetric efficiency, (which you won't get but it is a nice number to work with), multiply your displacement by your engine rpm's which will give you cc's per minute, now divide this by 1000 to give you litres per minute or divide by 28.317 to give CFM, (cubic feet per minute).
This is for a 2 stroke engine, for a four stroke divide final results by 2.
eg. A 95cc 2 stroke saw at 12500 rpm would draw 1187.5 LPM of air, or 41.94cfm.

Are you sure you divide a 4 stroke by two? Those pistons are still attached to the crank, turning, and displacing air, just like a 2 stroke.

 

[mtngun]

No disrespect mtn but the issue of finer particulates going straight through the filter media is even widely accepted by Stihl Australia.

No disrespect, MCW, but if Stihl knew what they were doing, they would not have designed the filter system the way the did, having it bottom out before a good seal is formed. It's a terrible design.

 

[husq2100]

I'm sure I could do with some filter schooling but I believe a larger filter will indeed lower the pressure differential on the same saw. If a saw is sucking let's say 1000 litres per minute that means there is a given volume of air crossing every square centimetre of filter material per time unit. By increasing the filter area less air is being pulled through every square centimetre in the same time unit so both pressure and air velocity should be decreased.

Once again, could be wrong

my gut feeling tells me its not only the volume of air but the verlocity.......is there a verlocity difference in say a 372 compared to a 395???? I agree that in a perfect world the bigger filter would do as you say above, BUT........that would require perfect air flow around 100% of the filter....AND the same pressure/verlocity around the whole filter......once again I feel the design shape, air flow around, air box etc etc etc all play a roll.....Better media hell yes, but better overall design....lets hope that the new saws coming out get improved on the older models......looks like the 261 is a good example of that

 

[tdi-rick]

Are you sure you divide a 4 stroke by two? Those pistons are still attached to the crank, turning, and displacing air, just like a 2 stroke.

But the inlet valves are closed for the compression and exhaust strokes and efficiencies are no where near 100% either (unless supercharged)

Two strokes can have greater than 100% efficiency if running a tuned pipe, but only in a very specific part of the rev range.

 

[tdi-rick]

I'm sure I could do with some filter schooling but I believe a larger filter will indeed lower the pressure differential on the same saw. If a saw is sucking let's say 1000 litres per minute that means there is a given volume of air crossing every square centimetre of filter material per time unit. By increasing the filter area less air is being pulled through every square centimetre in the same time unit so both pressure and air velocity should be decreased.

Once again, could be wrong

my gut feeling tells me its not only the volume of air but the verlocity.......is there a verlocity difference in say a 372 compared to a 395???? I agree that in a perfect world the bigger filter would do as you say above, BUT........that would require perfect air flow around 100% of the filter....AND the same pressure/verlocity around the whole filter......once again I feel the design shape, air flow around, air box etc etc etc all play a roll.....Better media hell yes, but better overall design....lets hope that the new saws coming out get improved on the older models......looks like the 261 is a good example of that

This is some schooling I've received from isuzurover on filters.

Most filters operate in what is called the laminar flow regime (Re << 1). In this regime, the inertial capture probability/efficiency for particles ALWAYS increases with increasing filter face velocity. The caveat on this is that as inertia increases, the probability that particles will bounce off the fibre rather than adhere also increases as velocity increases.

It is hard to give an actual number - as it depends on a lot of factors, such as the elastic deformation ability of the fibre and the particle (to absorb the impact), etc. However, most air filters operate at v<1 m/s, and in this range, rebound is unually negligible.

So in short - yes, thereis some wisdom in what you were told. Also - as velocity increases, the effectiveness of the interception and DR (interception-diffusion combined) filtration mechanisms may become less effective as well.

This is one instance where the oil coating on the K&N may help - in reducing the likelyhood of particles bouncing off the fibre when they impact. HOWEVER - I saw some data from K&N filters which were used in F1 race applications (with catastrophic results). When tested under identical conditions (v = 10 m/s !!!), the filtration efficiency peaked at about 85%, then started to DECREASE at about 20 microns. This was all due to particle bounce - so under such extreme condionions, all sorts of strange effects can occur!

From here Air Filter Tests (Finally) - Australian Land Rover Owners if you want to see how a cotton gauze filter performs against cellulose fibre (paper) type.

 

[Stihlman441]

There has been excellent data posted on this subject in the past by TW and Lakeside -- which we can't find now due to the broken search function :bang: -- but the gist of the data was that a Stihl HD filter flows way more than the saw requires.

Stihlman441, I blew up your photo to better see the dust. It's not that bad, but ...... I agree that any visible dust is unacceptable on a pro saw.

However, we haven't established where the leak is. Is the media leaking, or is the seal leaking ? People are jumping to the conclusion that the media is leaking, but how do you know ?

Stihlman, have you modded the attachment stud so that the filter can be screwed down tighter ? If you have not done so, there's nothing to lose by trying it.

I notice you are using the hard inner baffle. I recommend chucking the hard baffle, because the filter can bottom out on the baffle before a good seal is formed. Either use the foam inner baffle, or else run without any baffle. All the inner baffle does is deflect spitback when the saw is idling. It adds no value in the cut.

I notice you have stuck foam on the filter cover to help push the filter tight. The foam should help, but if you mod the attachment stud and chuck the hard plastic baffle, then the foam will not be necessary.

As I have stated in other threads, it may be that the HD2 filter is taller than the HD1, which would solve the seal problem without modding the stud or chucking the hard baffle. That's how I would solve the problem if I were Stihl's design engineer.

Thanks for your input,i have blued the filter base seals and re assembled them to make sure they seal,used grease around the screw hole and on seal edges,the only thing that works 100% is oiled uni filter i use on the 880,can use them on 660 but very hard to fit under filter cover.
This pic i have allready cleaned the surface with the paper towel,thats why it looks ok.

 

[MCW]

No disrespect, MCW, but if Stihl knew what they were doing, they would not have designed the filter system the way the did, having it bottom out before a good seal is formed. It's a terrible design.

I agree there are many flaws with that design. It will be really interesting how these HD2 filters perform on our hardwoods, fingers crossed

But the inlet valves are closed for the compression and exhaust strokes and efficiencies are no where near 100% either (unless supercharged)

Two strokes can have greater than 100% efficiency if running a tuned pipe, but only in a very specific part of the rev range.

Hey I agree that efficiencies aren't 100% Rick but a 4 stroke isn't 50% of the air intake of a two stroke either, unless I have completely understood something with the mechanics of internal combustion engines - it's a possibility though

 

[Justsaws]

Stack two filters with holes in the top of the bottom filter for flow from the top filter.
Open up the top of the bottom filter as much as you feel comfortable with.
You will need a longer bolt from the mount.
Toss cover in spare parts bin.

 

[Karl Robbers]

Are you sure you divide a 4 stroke by two? Those pistons are still attached to the crank, turning, and displacing air, just like a 2 stroke.

.
Sure do, Remember the 4 cycles Induction, Compression, Power and Exhaust.
Air only flows into the engine on the Induction stroke, the inlet valve then closes and the mixture is compressed and ignited, the piston then travels downward whereupon the exhaust valve opens and the inlet valve closes, piston then rises up and the spent gasses are expelled.
2 stroke has no valves in the conventional sense, (except for 2 stroke blower scavenged diesels) and therefore inducts air every revolution. Hence the greater power to weight ratio of a 2 stroke.
This of course refers to a naturally aspirated engine at WOT, turbo or supercharged 4 strokes can achieve well over 100% volumetric efficiency, just as volumetric efficiency will drop at partial throttle settings.

 

[MCW]

.
Sure do, Remember the 4 cycles Induction, Compression, Power and Exhaust.
Air only flows into the engine on the Induction stroke, the inlet valve then closes and the mixture is compressed and ignited, the piston then travels downward whereupon the exhaust valve opens and the inlet valve closes, piston then rises up and the spent gasses are expelled.
2 stroke has no valves in the conventional sense, (except for 2 stroke blower scavenged diesels) and therefore inducts air every revolution. Hence the greater power to weight ratio of a 2 stroke.
This of course refers to a naturally aspirated engine at WOT, turbo or supercharged 4 strokes can achieve well over 100% volumetric efficiency, just as volumetric efficiency will drop at partial throttle settings.

Thanks for the explanation Karl and that explains it perfectly. I'm not as think as I smart I am Those damn valves done me in...

 

[masculator]

HD2 filter availability

Ok Today I spoke to my stihl rep and the HD2 filters although available, there are no stock in Australia at present and they are on back order. I have ordered one but it is about 6 weeks before they will have stock in the country. They are $55 approximately. I suggest you place an order now if you want one.

 

[AUSSIE1]

For what you pay for the damn things they should be fitted as standard.

 

[masculator]

For what you pay for the damn things they should be fitted as standard.

I agree! but, for the peace of mind and lack of hassle I am just going to buy one. They are not standard because for a lot of stuff the standard hd filter is sufficient.

 

[porky616]

not bad price compared to the extreme kit, just have to wait and see if its really that good i guess

 

[young]

Ok Today I spoke to my stihl rep and the HD2 filters although available, there are no stock in Australia at present and they are on back order. I have ordered one but it is about 6 weeks before they will have stock in the country. They are $55 approximately. I suggest you place an order now if you want one.

true but if you think about it, if these hd2 works for the fines then its cheap insurance i say.

my 660 was $1100 and $55 is only 5% of the cost of my saw. i paid more in taxes when bought it.

iam sure its even a smaller percentage for you down under.

For what you pay for the damn things they should be fitted as standard.

i agree, i wish they have a trade in program, so i can get on for my 441.

 

[MCW]

true but if you think about it, if these hd2 works for the fines then its cheap insurance i say.

my 660 was $1100 and $55 is only 5% of the cost of my saw. i paid more in taxes when bought it.

iam sure its even a smaller percentage for you down under.



i agree, i wish they have a trade in program, so i can get on for my 441.

RRP on a new MS660 here is around USD$2100

 

[2dogs]

Why is Redgum so dusty? Is it hard or dry or both, is it as dusty green as dry? Do you have other gums that are just as dusty?

 

[young]

RRP on a new MS660 here is around USD$2100

ouch. well the AU 660 comes with dual port and roller chain catcher. haha

 

[Stihlman441]

And a high out put oiler as well