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General Category >> Rubber Side Down! >> BASIC MATH QUESTION? -- Goofy Mini-Muffler build..
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Message started by teabowl13 on 07/28/12 at 15:33:40

Title: BASIC MATH QUESTION? -- Goofy Mini-Muffler build..
Post by teabowl13 on 07/28/12 at 15:33:40

So, Savage Math Geniuses... here's the thing...
(Exhaust geniuses feel free to chime in as well...)

I have an older muffler that I want to adapt to fit the Savage, but it's from a 250cc dirt bike. The outlet diameter is only 3/4" BUT.... there's plenty of room to drill out more holes around this outlet so that there is more flow going through the muffler.

The stock Savage has an outlet of about 1.3" according to Lancer, or better yet, around 1.5" would be optimal.
That would mean I need an extra 3/4" worth of outlet hole, Right?

I want to drill 6 holes; that's what I think will look right aesthetically.
So does that mean I need to add 6 holes at 1/8" each to get a total of 1.5" of outlet?

I don't want to drill too many, or make it too open; I can always enlarge them later as I tune it...
I'm looking to get somewhere close to stock; slightly more open.

Title: Re: BASIC MATH QUESTION?
Post by teabowl13 on 07/28/12 at 15:40:56

Here's a pic of it mocked up just for fun.
The magic marker lines are where I plan to drill, but I just don't want to go drilling into it until I know what I'm doing...

Title: Re: BASIC MATH QUESTION?
Post by teabowl13 on 07/28/12 at 15:47:32

As you can see, it's tiny. There won't be any glass packing inside of it at all, so the internal screen will simply act as something of a baffle. I expect it to be quite loud, which I'm not thrilled with, but I have it lying around, and I rather love the looks of it. I may try to install some extra baffling further down inside the connector pipe...

Title: Re: BASIC MATH QUESTION?
Post by rfw2003 on 07/28/12 at 15:51:32

with just some quick calculation to get approx the same area of opening as a single 1.5" diameter you would need to add six 1/4" holes with the 3/4" single hole to equal the same open area

Title: Re: BASIC MATH QUESTION?
Post by teabowl13 on 07/28/12 at 16:01:38

Thank you sir!
I had a feeling my "gut-instinct-math" was off. 1/8" holes seemed too small...

Title: Re: BASIC MATH QUESTION?
Post by rfw2003 on 07/28/12 at 16:06:08

anytime, when your dealing with tube, ya gotta figure the area of what you want compared to what you have, then go from there, It doesn't really conform to just adding what would equal the same diameter such as 2 3/4" wouldn't flow the same as 1 1.5" tube.

R.F.

Title: Re: BASIC MATH QUESTION?
Post by rfw2003 on 07/28/12 at 16:22:02

Opppss I missed a step on the math. You need 6 1/2" holes. I forgot to square the radius to get the diameter. ::)

Title: Re: BASIC MATH QUESTION?
Post by Serowbot on 07/28/12 at 16:28:20

I'd try it like it is first... It's only gonna' get louder as you drill...

Title: Re: BASIC MATH QUESTION?
Post by Oldfeller on 07/28/12 at 16:32:23

+1 on what Serowbot just said,

if you know it is gonna be too loud now why drill holes in it to ruin it and just make it noiser ....

Title: Re: BASIC MATH QUESTION?
Post by Boule’tard on 07/28/12 at 16:36:09

Practically speaking, I like Serowbot's idea of trying it as-is first, and then maybe do small increments of drill-listen-drill-listen.. ;)

Title: Re: BASIC MATH QUESTION?
Post by arteacher on 07/28/12 at 17:56:12

That is a great math problem for my students! Thanks!

Title: Re: BASIC MATH QUESTION?
Post by teabowl13 on 07/28/12 at 20:50:35

I know that if I don't drill it out, the bike will run like crap if it runs at all. 3/4 diameter opening for the exhaust on this bike is way too small; that's half the size of the rest of the header pipe.

I drilled it out with 6 1/2" holes to start. That seems to make sense to me. It'll be a couple of weeks yet before she's running; still needs all of the wiring redone and routed, but if I need to go bigger then, then I will.

It's going to be loud no matter what simply because there's no glass packing what-so-ever in that thing. The muffler has a 3/4" perforated tube running down the length of it inside; originally the space around that tube would have been packed with glass to quiet the noise. By drilling holes into the outer ring of the endcap, and around the bottom end as well, where it fits into that exhaust pipe piece, the exhaust will flow through both the outside chamber and the inside chamber. I expect this will act similarly to having a steel baffle in a straight pipe, but who knows!! I'll have to wait until it's running to find out.

(Might have to look for an alternative to pass inspection with!!)
This may end up as bench sculpture, or lawn art, but hell, I had the muffler already, and that piece of exhaust pipe only cost me $5...

Title: Re: BASIC MATH QUESTION?
Post by HondaLavis on 07/29/12 at 16:38:46

Here's some math with work shown:

You're goal is an equivalent to 1.5" diameter exhaust opening. pi*R^2 = circular area. 3.14*0.75^2 = 1.76625"

You're current exhaust HAD a 0.75" diameter opening. 3.14*0.375^2 = 0.4415625"

Given 3.14*0.125^2 each additional 0.25" hole adds 0.0490625"

Subtract what you started with from your goal: 1.76625-0.4415625 = 1.3246875" That's the amount of area you would need to make up in order to reach your goal.

How many 0.25" holes is that? 1.3246875/0.0490625 = 27. You would need 27 0.25" holes.

You've already drilled 6 0.5" holes. 3.14*0.25^2 = 0.19625"
0.19625*6 = 1.1775"

So you've already taken care of 1.1775" of the remaining 1.3246875" 1.3246875-1.1775 = 0.1471875"

The difference between your 1.5" equivalent goal and your current combination of openings is 0.1471875" That divided by our given area for a 0.25" hole is 3. If you don't like what you've got now, drilling 3 0.25" holes might get you there.

Sorry for being long winded. Just wanted to make sure everything was out on the table. I still agree with Serowbot; try it how it is before you go all out.

Title: Re: BASIC MATH QUESTION?
Post by teabowl13 on 07/29/12 at 20:59:13

Thanks HondaLavis.

I've already drilled six .25" holes, but you're saying I need 3 more.
Visually speaking, I can't add more holes, but I can make the six holes I have now larger. What size should they be?

At this point it's all guesswork, (I actually ovalled the holes out a bit with the drill since I was drilling into a 45 degree surface anyway) so I am going to leave it at that for now. once I get it running I will decide how it's working as we get it tuned up.
I can certainly drill the holes out larger if I need to, but the cool thing about this little mini-muffler is that it's made to be packed, so if I go too far and need to restrict it some more, I could open it up and stuff some stainless scrubby pad material inside to both quiet it some and to slow down the flow, so I'm not too worried.
Regardless of the tuning, it may end up way too loud to pass inspection anyway, in which case I'm back to square one; but hopefully it'll do the job.

I'm going to be welding a small 4" section of baffle into the connector pipe as well, so that should help, (That was Lancer's suggestion to me a while back.) and there's room in there to squeeze another 4" piece as well if I want to do that, so I think I have a few options here...

No matter what, I'm expecting it to sound pretty mean.... >:(

Title: Re: BASIC MATH QUESTION?
Post by teabowl13 on 07/29/12 at 21:06:48

Here's what the holes look like now drilled out in the back end...

Title: Re: BASIC MATH QUESTION?
Post by teabowl13 on 07/29/12 at 21:13:10

Here's a shot of where the other end of the MINI_MUFFLER fits into the exhaust tubing.
That connector piece is a 1.75" ID standard exhaust tailpipe piece; it has a 45 degree bend and a 45 degree slash cut at the end, which is why the connection looks a little funky, but I think it will look great once it's welded up...
After marking where the muffler sits inside the pipe, I drilled a whole mess of small holes into the pipe to allow more flow-through. I wasn't concerned about these having the exact amount of area since they are in the middle of the exhaust; (it's the holes at the very end that will determine total flow) so these are all about 1/8" but there are 17-20 or so of them.... more than enough to do the job, and hopefully these will break up and scramble the exhaust flow and have a good baffling effect.

Title: Re: BASIC MATH QUESTION?
Post by teabowl13 on 07/29/12 at 21:16:01

Here's a view looking into the inlet end of the mini-muffler.
It looks gigantic because of the close-up-ness of the photo, but that opening is only 3/4". You can see the screen that goes down inside the muffler; it's a 3/4" ID tube of perforated metal running through the middle of it...

Title: Re: BASIC MATH QUESTION?
Post by Boule’tard on 07/29/12 at 21:17:40

Whell, ellipses? CHANGE THE PROBLEM on us why don't ya ;D

Ok <math hat on>
You drilled out 6 half-inch holes on a 45 degree angle. The area of an ellipse is pi times the short radius times the long radius. The short radius is half the diameter of your drill bit = .25in. The long radius is half of your bit diameter/cos45 = .354in. So the area of each hole is pi*.25*.354=0.278in^2. The total area you drilled out with the 6 holes is 1.67in^2. Hope that helps.

Title: Re: BASIC MATH QUESTION? -- Goofy Mini-Muffler bui
Post by teabowl13 on 07/29/12 at 21:41:20

OH!
You must assume I drilled an ACTUAL ELIPSE! Well... let me tell ya...
I drilled these out by hand, just holding the thing down on the workbench and going for it.
When I say ellipse, what I mean is... I drilled out very small pilot holes to get started, then drilled them out with the 1/4" bit... THEN... while holding the little bugger firmly down to the bench with the drill bit running, I slowly lowered the drill down at an angle which ovalled out the holes a bit.

There's no exact science or math involved in the actual drilling process, so at this point the math is really more hypothetical than anything; although I DO very much appreciate you geeks putting your thinking caps on for this one! (I kid... I kid...) ;D

At this point I think the math has gotten me close enough to what I am looking for, and now I just need to get the bike running and see how she works in real life and fine-tune it from there based on seat-of-the-pants feel, and whether or not it's completely deafening...

CHEERS!

Title: Re: BASIC MATH QUESTION? -- Goofy Mini-Muffler bui
Post by Boule’tard on 07/29/12 at 22:14:00

I'm sure your drilling skills are as good as my math skills.

If you were shooting for the equivalent of a 1.5" diameter hole (1.76in²) then I'd say you've got that and then some.

The 3/4" hole gives you 0.44in² and the other 6 holes are 1.67in², totaling 2.11in²

So if there is a bottleneck, it is probably not at the end of your muffler.. time to bust out the earplugs :D

Title: Re: BASIC MATH QUESTION? -- Goofy Mini-Muffler bui
Post by teabowl13 on 07/29/12 at 22:31:21

SORRY BOULETARD...
I mis-typed that last post (just corrected it....) those holes are 1/4", not 1/2" BIG DIFFERENCE!

Either way, like I said, I feel like I have room to play with it iin a few different ways if I need to; drilling the holes out larger, or adding more baffling inside the connector, or stuffing the muffler with steel wool, so I'm hoping I can tune it to my taste once it's running.

Title: Re: BASIC MATH QUESTION? -- Goofy Mini-Muffler bui
Post by John in Kalifornia on 07/29/12 at 23:42:18

If it falls off you can always use one of these as a replacement.

John in Kalifornia

http://p1.bikepics.com/2012%5C07%5C30%5Cbikepics-2435254-200.jpg

Title: Re: BASIC MATH QUESTION? -- Goofy Mini-Muffler bui
Post by justin_o_guy2 on 07/30/12 at 05:08:09

I like it,