RDP: your 026 muffler pics

[shalenkur]

first is from inside of muffler, two extra 7/32" holes.

then the bent deflector on front of muffler under heat shield that could also be drilled for even less restriction.

then area to be port-matched (mine still needs work on the right side).

hope you find these helpful.

 

[RDP]

Great pics

Hi shalenkur,

Many thanks for the pics, sure helps understand clearly as a picture is worth a thousand words.

 

[timberwolf]

True you can always cut more out later, but I would be conecting them 3 lil holes together, 1 larger port will out flow 3 smaller ones. and keep a within a recpectable port to exaust opening ratio.

 

[RDP]

Hi

Anyone who is knowledgeable in chainsaw mods,what is the maximum hole size that can be drilled in the 026 muffler and what about a 044 ?

Thanks to all,

 

[timberwolf]

There are many more knolegable than I but here is a link to a little test I did a couple years back

260 muffler mod test data

From a recent port map of a stock 260 I measure the exaust to be 23 x 11.5 mm oval in shape roughly. which is roughly 235 square mm.

multiplied by 1.5 = 352 square mm, have herd in the range of 1.5-1.6 times the exaust port is a good place to be.

The outlet on my 260 is 35 mm x 10 mm = 350 square mm, works well, though I may need to make it a bit bigger.

hope it helps
Timberwolf

PS knowing what I know know I would not make it rectangular, but rather oval. If/when I open it up some more I will turn the rectangle into an oval.

 

[glens]

That information is available in a formatted and corrected form in my post to a similar thread here

Glen

 

[rustyb]

Timberwolf,

Just curious as to why you would make the hole oval?

r

 

[timberwolf]

It is likely a very minor point, but fluids (gasses or liquids) don't flow well through square holes, seeing that there is room enough it's not any amount harder to make a more rounded hole wich flows beter with the same given area. Also there are other theroretical influnces to flow charicteristics that don't favor corners and sharp edges. Thats the flow theroy.

Most of the resistance to flow occures at the edge of the orfice its best to reduce the length of the surface.

10x35mmm outlet port has a perimeter of 90mm for an area of 350 sqr mm,
21.1 mm diameter circular outlet port has the same area but only a 66.6 mm perimeter. an oval is not as good as a circle, but better than a rectangle. Circular opening would not fit the shape of the muffler as well in the case of the 260.

Wave theroy is another game as well, wich is harder to nail down but also could factor in.

 

[Ranchero50]

Timberwolf, interesting about flow theory... I've been building ported V8's for years with excellent results. How much can you play with ports on a two stroke before the flow timing goes to crap? Can you increase the length of the port like adding a cam with more duration or go wider on the bore for more lift? what about playing with timing on a two stroke vs a four stoke?

Muffler mods seem like the tip of the iceberg for making a hard runner..


Jamie

 

[rustyb]

Timberwolf,

That's what I thought. When I opened mine, I had the same thing in mind. My hole is still rectangular but I was careful to make the radius's as big as possible. I don't recall the width but it was slightly larger than the hole you had done in your tests. The height though was shorter so in essence, I ended up with a stubby rectangle with a large radius on each corner. And, thinking along the same lines, I also centered this newly enlarged opening with the deflector plate......all in hopes to get a smoother exhaust exit.

Thanks for taking the time to perform then post those tests. Wish there were more like that.

r

 

[timberwolf]

Jamie, It is very well possible to do this. but there would appear to be many chalenges. As you must well know working on V8's each cam/rocker ratio/valve change creates it's own set of neatives and positives. If one justs goes at a chain saw without understanding all that is at play it would be quite likely that the result could well be worse than the stock saw. working inside a small one piece casting like a saw head would offer chalenges of its own and require specilized tools to do a proper job.

There is a bit of info scattered about the site if you seach "porting", also the members like ehp who know a great deal about what works and what does not and who are set up with the tools to do a good job.

pm'd you some links I found for reading material, all the links are already on AS so I would repost redundat info.

 

[glens]

I think the short answer would be that the single act of monkeying with the ports on a two-stroke can be akin to doing both that on a 4-stroke as well as altering its cam profiles/timing in one fell swoop.