Wooooooooo DAWGY!!!!!!

parrisw · January 17, 2007, 10:30:18 AM

Ok, so the total exhaust outlet area has to be 85% of the exhaust port??

Thanks

StuBC · January 18, 2007, 08:02:57 PM

Anyone want to post a photo of what you are doing? Sounds interesting, it would be cool to visualize.

parrisw · January 19, 2007, 12:04:44 AM

Here is one thats been done, I want mine to come out like this.

TexasTimbers · January 19, 2007, 03:37:25 PM

I "opened up" my muffler and then realized I hadn't considered the factory outlets in my computations, so I took a broken recip blade and clamped it in there to partially restrict the flow. Real hi-tech engineering. Now you see why I cautioned you to get all the facts and to figure all your openings and the %mesh restriction you'll get for the spark arrestor.
I did it on my way out into the field and did it in a hurry. Don't do that and save yourself from re-doing it. :

It looked okay until I stuck the sawzall blade inb there. I would have probably been okay to leave it wide open but didn't want to blow my favorite saw up so went with the safer-than-sorry philosophy.

parrisw · January 19, 2007, 09:56:04 PM

I agree don't rush on stuff like that, the one that I posted I think the stock outlet has been blocked off, and then the two front ports added, looks pretty cool though.

TexasTimbers · January 20, 2007, 09:36:25 AM

that's the way i am going to do mine too parrisw. I saw a pic last year similiar to the one you posted that was da bomb. The new muffler is waiting for the unibit . . . . . . . . 8)

woodmakr · February 15, 2007, 09:06:47 AM

Hey all,

You can still get to the old Madsens site by using the WayBackMachine. Try this link: http://www.archive.org/index.php then type in www.madsens1.com and have fun.

leweee · February 15, 2007, 12:10:25 PM

woodmakr.....thanks for that link. 8)

Carb Ajustment Link

parrisw · February 16, 2007, 12:14:06 AM

Just bought a ported 394 muffler of Ebay, like the one in the pic I posted, should have it tomorrow. Cant wait to try it out, will report back.

parrisw · February 16, 2007, 11:09:22 PM

Ok, these numbers just don't add up, with just the two front ports on the modded muffler, the area of the outlets is way more then 85% of the exhaust port area. Maybe I m doing this wrong.

Each port on the muffler is 13/16 ID, plus it has the stock port which the baffle has been remove and the port opened up. Im thinking of closing off the stock port leaving just the two front ports.

The exhaust port on the cylinder measures 1 3/8 x 5/8" its been a while since I ve done any math. The way this muffler is modded is the way I ve seen many others done. And I m a little baffled at this. What am I doing wrong.

TexasTimbers · February 17, 2007, 12:05:43 AM

wow. woodmakr that site is cool thanx.

jokers · February 17, 2007, 01:50:22 PM

Quote from: parrisw on February 16, 2007, 11:09:22 PM
Ok, these numbers just don't add up, with just the two front ports on the modded muffler, the area of the outlets is way more then 85% of the exhaust port area. Maybe I m doing this wrong.

Each port on the muffler is 13/16 ID, plus it has the stock port which the baffle has been remove and the port opened up. Im thinking of closing off the stock port leaving just the two front ports.

The exhaust port on the cylinder measures 1 3/8 x 5/8" its been a while since I ve done any math. The way this muffler is modded is the way I ve seen many others done. And I m a little baffled at this. What am I doing wrong.

Maybe I can help. Let`s start with the area of each port and since you stated 13/16 ID I will assume circular ports.

To determine the area of a circle the formula is π(← that is supposed to be pi but php doesn`t play nice)r² so your equation would look like this, 3.14(13/32 x 13/32) because 13/32 is one half the diameter(the radius) of 13/16. To convert 13/32 to a number friendlier to use, divide 13 by 32 which results in .40625. I`m going to round this number to .406, so then,

3.14(.406 x .406)
3.14(.164836) which equals
.51758504 which I will round to .518 so then,
.518 x 2(two ports) = 1.036(round to 1.04) square inches of open port area. If you screened this port with mesh you would have to use the appropriate open area factor for your size screen to determine your final open area. Hint: You can make a port which is too big, smaller.

Now let`s address the cylinder`s exhaust port area which is 1 3/8 x 5/8. We can divide 3 by 8 so we get 1.375 and 5 by 8 which equals .625 so the area calc for this port is 1.375 x .625 resulting an open area of .859375 square inches which I`ll round to .859 in². So to determine the percentage of muffler port to cylinder port area we will divide 1.04 by .859 which equals 1.21 or 121% open area. Way too big for any saw near stock. You need to perform more detailed calculations using port/time areas, compression, bmeps, etc. to dial in any more precisely than the 85% guideline which works quite well with most saws stock or mildly ported. Usually though, ports larger than 85% just means louder not more powerful.

Does this help?

BTW, somebody check my math! ;D ;)

parrisw · February 17, 2007, 07:46:33 PM

"jokers" Thanks that does help, yes I was doing the area of a circle wrong. And Ya I thought that the modded muffler had too much area by just looking at it. Im going to close off the stock port on it, and just leave the the two front ports.

Thanks again.

parrisw · February 17, 2007, 07:52:48 PM

Ok, I went through this again, and it doesn't make any sense, if I go by the formula 85% of the port area then that means the stock port is too large???

Stock ex port area is .86 sq inches

stock muffler port measures out at .82 sq inches

That means 85% of the port area you should have a muffler opening of .73sq inches, smaller than the stock muffler opening. Just doesnt make any sense, after hearing all these people of modding their muffler???????????? What

Just had a thought, I guess since the stock port has a screen, that makes it smaller. But that would still mean, that if you do any muffler mod, the muffler port area will still be too large?????????

jokers · February 18, 2007, 12:57:43 AM

Quote from: parrisw on February 17, 2007, 07:52:48 PM
Ok, I went through this again, and it doesn't make any sense, if I go by the formula 85% of the port area then that means the stock port is too large???

I wouldn`t say that and I am assuming that we are talking about your 394 which isn`t the latest emissions choked version of that powerhead so it is very likely that your muffler is not unduly restrictive.

Quote from: parrisw on February 17, 2007, 07:52:48 PM
Stock ex port area is .86 sq inches

stock muffler port measures out at .82 sq inches

That means 85% of the port area you should have a muffler opening of .73sq inches, smaller than the stock muffler opening. Just doesnt make any sense, after hearing all these people of modding their muffler???????????? What

Just had a thought, I guess since the stock port has a screen, that makes it smaller. But that would still mean, that if you do any muffler mod, the muffler port area will still be too large?????????

My calculations show your stock measured muffler port to be nominally 95% of of the cylinder exhaust port. Adding a screen can easily reduce the open area by 10% and this is why so many guys have removed those screens over the years.

BTW, 85% is a pretty good thumb rule but hardly cast in stone. I even referred to it as the 85% guideline because that is how I see it. One reason that the Uni Bit method is so handy, it`s easy to start on the small side and then work your way up incrementally.

Al_Smith · February 18, 2007, 08:28:29 AM

Here is a point of view or opinion on the suject of muffler modifications.

Often times people expect the saw rpm s to automatically jump a couple of thousand rpm s .This is not neccessarily true.Rpms out of the wood just make noise,it's the cut speed in the wood that counts.

The whole idea behind reworking a muffler is to allow more fuel,in a usable mixture to be used within the engine for power.If bigger were better,just remove the muffler but trust me it won't run as good,been there and done that.

Little stub pipes and megaphones look kind of cool and add to a certain amount of austetics but do little if anything for the overall performance.

Because I have so many saws ,covering the whole ranges of sizes ,I tend to be rather conservative on saw modifications.A modest gain of 10 to 15 percent in my way of thinking would be just about right for an everyday usefull saw.

The actual outlet size for the muffler has long been a debated issue on many internet forums .Just remember it does little good to just make the things run louder and blow fuel out the muffler with little gains.My suggestion is to do a little bit at a time and stop when you are comfortable with it.

jokers · February 18, 2007, 09:22:42 AM

Quote from: Al_Smith on February 18, 2007, 08:28:29 AM
Here is a point of view or opinion on the suject of muffler modifications.

Often times people expect the saw rpm s to automatically jump a couple of thousand rpm s .This is not neccessarily true.Rpms out of the wood just make noise,it's the cut speed in the wood that counts.

The whole idea behind reworking a muffler is to allow more fuel,in a usable mixture to be used within the engine for power.If bigger were better,just remove the muffler but trust me it won't run as good,been there and done that.

Little stub pipes and megaphones look kind of cool and add to a certain amount of austetics but do little if anything for the overall performance.

Because I have so many saws ,covering the whole ranges of sizes ,I tend to be rather conservative on saw modifications.A modest gain of 10 to 15 percent in my way of thinking would be just about right for an everyday usefull saw.

The actual outlet size for the muffler has long been a debated issue on many internet forums .Just remember it does little good to just make the things run louder and blow fuel out the muffler with little gains.My suggestion is to do a little bit at a time and stop when you are comfortable with it.

Excellent post Al!

parrisw · February 18, 2007, 02:45:27 PM

Ok, thanks again guys, maybe I jumped the gunn a little on putting this muffler on, I will close off the stock port on this modded muffler and se what happens. Im thinking that the stock muffler with baffle removed would be about right. But this one sure sounds cool.

Thanks again

Will

jokers · February 19, 2007, 09:37:14 AM

Hi Will,

Since you already have the muffler modified, why not experiment a bit with it? Run it as is and time a few cuts and then block the factory opening with something, maybe some wadded up aluminum foil and then time a few more cuts. It wouldn`t need to be an air tight seal, just enough restriction to let you know whether or not you need to mess with closing the stock port. You can also close the stock port by varying degrees by squashing the deflector down.

parrisw · February 19, 2007, 02:02:59 PM

Yes good plan, I figured since the two front ports are already too big, I figured closing the stock opening and leaving the two front ones would be better??

Thanks again for all your guys help. I still haven't cut with it yet with the mofifed muffler on it.