Benefits to adding a dual port or bark box muffler

[Lightning Performance]

There is benefits of front exhaust flow from the stock muffler modification stub to that of a side stub modified muffler . I find that a short blowdown saw & a front discharge increases rpm & horsepower gain where as side discharge & longer blowdown rates enhance available midrange torgue values . Strato & reed valve saws really wake up & run cooler with a proper muffler modification !

But why side exits?

My best guess is linear dynamic flow. At high rpm you have effectively less volume once you past your VE or stalling of the air coming in a naturally aspirated intake port. The muffler has a stronger pulses when the side exits are used but it still see more gasses to release as RPMs go up so getting it all out the fastest way or upfront to release more backpressure vs having to turn will get it out faster. We all know it's louder. Noise is energy leaving the tool. The turn takes longer and flows less around rough edges vs the open front cover or open hole. The side exit turns the gasses twice. That takes time and energy. Maybe only 0.0004 of a second more at 10k but it matters as you guys say it does based on testing. Screens even giant ones with larger holes help with noise. Quiet is good most times once we mess with stuff just not practical or light weight.

 

[North by Northwest]

Buy why side exits?

My best guess is linear dynamic flow. At high rpm you have effectively less volume once you past your VE or stalling of the air coming in a naturally aspirated intake port. The muffler has a stronger pulses when the side exits are used but it still see more gasses to release as RPMs go up so getting it all out the fastest way or upfront to release more backpressure vs having to turn will get it out faster. We all know it's louder. Noise is energy leaving the tool. The turn takes longer and flows less around rough edges vs the open front cover or open hole. The side exit turns the gasses twice. That takes time and energy. Maybe only 0.0004 of a second more at 10k but it matters as you guys say it does based on testing. Screens even giant ones with larger holes help with noise. Quiet is good most times once we mess with stuff just not practical or light weight.

Sometimes a laminar " smooth flow " provides benefits , while within other perimeters a more dynamic or turbulent flow profile can provide the same benefits !

 

[Jasonrkba]

I remember reading an article years ago about dirt bike mufflers and the length of the pipe has an impact on response. A shorter pipe would provide a snappier response while a longer pipe helped with top end. I could be talking out of of my you know what but would be interested your guys thoughts?

 

[Evan]

No your exactly right. 4stroke motocross bikes even benifit from certain pipe lengths and expansion chambers.

 

[pioneerguy600]

I read somewhere that you want to limit the exit port to 60 percent of the actual exhaust port. I would love to here what you guys consider appropriate. If it's to open it can cause a lean condition by removing it's ability to scavenge. Is this thinking correct?

65% side exit for work saws, for race 100% exit anywhere, saw doesnt run long enough to be annoying.

 

[Lightning Performance]

Sometimes a laminar " smooth flow " provides benefits , while within other perimeters a more dynamic or turbulent flow profile can provide the same benefits !

In exhaust theory we waste energy and velocity without straight laminar flow yet turbos do a fine job of recycling wasted energy. Now the clocked poppet valves in cylinders vs ones not "clocked" around so much changes the RPM of your long side flow potential to the point of shutting down a head that has more then two direction changes or dumps into a wall area. Four direction changes will surely kill it for peak performance but can add so much power or torque under the curve you wouldn't want the top end performance upgrade to more power in numbers only not overall power made under the curve. That interest me more then any piston port controlled engines. These make 180 to 270 direction changes. Car two valve heads can be from 90 to 360 direction changes. Chrysler Hemi and Clevland Ford heads started that whole debacle with tumble vs fall and it still holds true. Many heads designed to run at 9k, no more, just won't go to 11.5k yet the 11.5 head couldn't move our pickup trucks up a decent hill from a low speed or stopped. The operation widow is where they all live and die smooth flowing or not. Turbulence seems to be a good thing in the combustion chamber area only. Everywhere else it generally hurts the objectives. Dumping an NA charge directly in the center of your toilet will always be king at the track provided with proper gearing and worth nothing in traffic without a CVT to reach operating speeds viable for common use. The in line flowing valves run so poorly at low speeds it's almost unimaginable. Um... raw fuel anyone? Cough, cough, cough,

 

[North by Northwest]

In exhaust theory we waste energy and velocity without straight laminar flow yet turbos do a fine job of recycling wasted energy. Now the clocked poppet valves in cylinders vs ones not "clocked" around so much changes the RPM of your long side flow potential to the point of shutting down a head that has more then two direction changes or dumps into a wall area. Four direction changes will surely kill it for peak performance but can add so much power or torque under the curve you wouldn't want the top end performance upgrade to more power in numbers only not overall power made under the curve. That interest me more then any piston port controlled engines. These make 180 to 270 direction changes. Car two halve heads can be from 90 to 360 direction changes. Chrysler Hemi and Clevland Ford heads started that whole debacle with tumble vs fall and it still holds true. Many heads designed to run at 9k, no more, just won't go to 11.5k yet the 11.5 head couldn't move our pickup trucks up a decent hill from a low speed or stopped. The operation widow is where they all live and die smooth flowing or not. Turbulence seems to be a good thing in the combustion chamber area only. Everywhere else it generally hurts the objectives. Dumping an NA charge directly in the center of your toilet will always be king at the track provided with proper gearing and worth nothing in traffic without a CVT to reach operating speeds viable for common use. The in line flowing valves run so poorly at low speeds it's almost unimaginable. Um... raw fuel anyone? Cough, cough, cough,

All that automotive 4 cycle refraction of flow dynamics is lost within a saw application were boost pressure is non existant & only atmospheric pressure is applicable . Although laminar & turbulent flow curves are applicable within scavenging , within tuned pipe applications where harmonics are critical to efficient performance gains !

 

[Jasonrkba]

Am I the only one who has to read this stuff really slowly. Just a thought I've had. I picture the stream of flow like a roller coaster. Sometimes a properly placed turn or corkscrew helps pick up momentum. The obstacle I always face when trying to design a pipe is where and how to place these turns without making the pipe so big and clumsy that you don't want to run it. Weight is a whole different issue. I don't have a tig welder so find myself using heavier steel than necessary so I can stick weld it. I think for most folks who make money with there tools performance gains are nice but getting that heat out is the goal so that your tool last longer. Creating this momentum is almost impossible if you are trying to direct that flow to two different exit points.

 

[aokpops]

I was told back in the 70s take the baffles out of your dirt bike make it run better! What a load of crap no mod is this easy an engine is an air pump if you don't let more air in no more will get out

 

[singinwoodwackr]

My stepson keeps wanting to put one of theses bark boxes on his 046. His 046 already has the stock large port and a stock dual port cover as well. I told him forget the bark box and just tune properly what he has.

My 10mm pin 044 (1993) has a stock large port exhaust and no dual port and runs like a champ without any extra holes in the muffler.

Gary

It would make no difference

 

[singinwoodwackr]

I think my new 500 I is pretty damn loud stock.

No real baffling inside is why. Open up the stock hole a bit is all you need to do, imo. Mine is not much louder after the mod but seems to run cooler.

 

[Lightning Performance]

Am I the only one who has to read this stuff really slowly. Just a thought I've had. I picture the stream of flow like a roller coaster. Sometimes a properly placed turn or corkscrew helps pick up momentum. The obstacle I always face when trying to design a pipe is where and how to place these turns without making the pipe so big and clumsy that you don't want to run it. Weight is a whole different issue. I don't have a tig welder so find myself using heavier steel than necessary so I can stick weld it. I think for most folks who make money with there tools performance gains are nice but getting that heat out is the goal so that your tool last longer. Creating this momentum is almost impossible if you are trying to direct that flow to two different exit points.

The biggest problems come from dry flow assumptions about wet flow characteristics simply put. Your roller coaster saps power it never adds anything. So so many people forgot about fuel remaining in suspension and get the fallout back in the fog. If you pour fuel in it your not necessarily going to burn all of it. Now your wasting it like racing does for various others reasons mostly cooling related depending on the fuel and event. Nascar saves as much as possible yet top fuel almost pours it in. Just the combustion chamber alone and how it becomes it's final shape is very important per application. Sharp edges or not and small tidbits start to add up real quick in tiny engines. Quarter inch of this and a millimeter of that boom

 

[singinwoodwackr]

For the thinking box

View attachment 1046323

That has to be loud, lol

 

[singinwoodwackr]

I just finished this one for my 500i, but I have not had a chance to take it out for a run yet. It’s just the stock cover with a 5/8” od stainless tube welded in.

Similar to what I did but I kept a front deflection.

 

[Lightning Performance]

Here something to chew on.

Other changes were made to get a Stihl 180° transfers port to flow better then a bottom feed 90° transfer port like a Husky yet either one can flow about the same with other changes. What are the changes? I know what they are but many don't see the whole picture. Info is all right there in the acual designs. One has much less of something while the other has more and it isn't transfer port numbers or quads vs dual port transfers. Make them all quads for an even playing feild. Pretty simple math just checking everything. You rule out bore vs stroke or carb sizes. Airfilters won't matter either. You can't have both together in one design. A line in the sand has to be drawn about design and build type.

 

[North by Northwest]

Am I the only one who has to read this stuff really slowly. Just a thought I've had. I picture the stream of flow like a roller coaster. Sometimes a properly placed turn or corkscrew helps pick up momentum. The obstacle I always face when trying to design a pipe is where and how to place these turns without making the pipe so big and clumsy that you don't want to run it. Weight is a whole different issue. I don't have a tig welder so find myself using heavier steel than necessary so I can stick weld it. I think for most folks who make money with there tools performance gains are nice but getting that heat out is the goal so that your tool last longer. Creating this momentum is almost impossible if you are trying to direct that flow to two different exit points.

There is a basic design formula for the size & thickness of the header section & then the diameter of the 1st divergent section of the tuned pipe . Then the section of convergent piping slowly reduces the overall diameter back down to the stinger section of the tuned pipe which length is nominally 1/2 the length of the overall cross section of the header . The thickness of the tuned pipe is critical in providing efficient harmonics within the pipe to assist within scavaging & overall performance gains within either low or midrange rpm range horsepower & torgue spec's that are required . A simple muffler mod only reduces overall saw heat & does only marginally increase the overall saw performance . Other changes such as intake & exhaust port reworking & degree of timeing provide much more dramatic performance potential !

 

[North by Northwest]

Here something to chew on.

Other changes were made to get a Stihl 180° transfers port to flow better then a bottom feed 90° transfer port like a Husky yet either one can flow about the same with other changes. What are the changes? I know what they are but many don't see the whole picture. Info is all right there in the acual designs. One has much less of something while the other has more and it isn't transfer port numbers or quads vs dual port transfers. Make them all quads for an even playing feild. Pretty simple math just checking everything. You rule out bore vs stroke or carb sizes. Airfilters won't matter either. You can't have both together in one design. A line in the sand has to be drawn about design and build type.

The quad runner saws really improve with crankcase stuffers to reduce the overall crankcase volume .

 

[Evan]

Camt we just wing it and weld stuff together

 

[Seachaser]

No real baffling inside is why. Open up the stock hole a bit is all you need to do, imo. Mine is not much louder after the mod but seems to run cooler.

Pictures? Got one on order.

 

[North by Northwest]

There are numerous Cat delete video's on the internet showing proper muffler modifications to stock saw applications .