DIY Muffler Build

[Thrasher]

I got the sheet metal yesterday for free(would've been about $50) and ordered the j-bends from Summit for $28 with shipping. I just got the tracking info and the bends will be delivered today, woo hoo! I forgot there was a Summit warehouse in Reno, about 3 1/2 hours away. They're going to be a 3-chambered design measuring 10"x16"x4" with Helmholtz tubes and baffles set up like a Delta Flow from Flowmaster. I started a little lay out yesterday and am gona get busy today. Stay tuned for pics later.

[norm8332]

I can't wait to see the pics. Sounds good. Part #s etc would be good :)

[Thrasher]

I got all the bits and pieces fabbed up and about half the welding of one done. Damn FedEx didn't deliver, said the address did not exist. That's funny cause I've had 8 or 9 deliveries here from them in the past 2 months. :uhm: Oh well, I wasn't ready for them anyway. These better sound infuckingcredible! They are by no means easy to build with hand tools, an angle grinder and a mig running flux core. I'm taking pictures the whole way through and will post everything and a sound clip when they're on the car. Anyway, here's a sneak peak...

[Fatdaddy]

Lookin' good so far!

[norm8332]

Coming along good! I bet it will be loud.

[Thrasher]

Thanks. I should get a lot more done tomorrow. I spent a long time today getting everything ready and changing things around a couple of times. All I can say is they'd better sound!

[jkayner]

are you using some kind of muffler design program or are you just making up the design? I mean it looks good, but wondering if there is any science behind the layout. Just curious.

[Thrasher]

are you using some kind of muffler design program or are you just making up the design? I mean it looks good, but wondering if there is any science behind the layout. Just curious.

No, no muffler design program. I wish! I'm kind of crossing a Super 40 with a Delta 40 with a Delta 50 and connecting the center chamber, which is there for drone on the Delta 50, to the magical 28-1/2" long Helmholtz chamber that will sit on top of the outside of the muffler body. As far as layout and dimensions, it's the same as the Super 40 but as long as the Delta 50 and I'm kind of eyeballing off of cut-away photos. Also, trying to picture what the sound waves are going to do in the center chamber. Everything in the center chamber is either 30 or 60 degrees to everything else so the sound waves will bounce around and cancel themselves out. Hope it works!

[Devilish34]

don't forget the drain hole

[Thrasher]

I was actually thinking that would be a good idea, thanks for reminding me. Does anyone know how big and where they typically are? I've never seen or noticed a drain hole in a muffler so I don't know, but I remembered reading what happens to the Corsas that don't have them. I was also thinking it my not be necessary in a chambered style as the water would just blow out.

[GPDAN]

cant wait to see the end results.

[Thrasher]

Me too! I'll have them done by the end of this weekend for sure then on the car next weekend.

[-Ray-]

Too bad you aren't closer, I'd let you use my jig to fab up the pipes and tips.
I have a couple flanges if you are interested.

[BigRed585Lbs]

To say I'm impressed would be a gross understatement. Good work, and good luck with the outcome!

[TLS]

Why not incorporate the J-pipe INSIDE this muffler?

[96Prix]

Pretty interesting stuff. Certainly a unique undertaking.

[Thrasher]

Too bad you aren't closer, I'd let you use my jig to fab up the pipes and tips.
I have a couple flanges if you are interested.

That'd be nice. I was thinking about building a crude, one time use jig to get em just right.


To say I'm impressed would be a gross understatement. Good work, and good luck with the outcome!

Thank you!


Why not incorporate the J-pipe INSIDE this muffler?

Because it won't fit and if I made it fit flow would probably be obstructed.

The J's are due to be delivered again today so I'll probably get to finish one and post another pic.

[Thrasher]

Got nothing done today. It's been raining too much to break the ol welder out and I'm still waiting on FedEx:jerkoff:

[Thrasher]

Here's a recent pic. Haven't had a lot of time this week, but I' figure there's only about 30mins left of welding, cleaning and painting, and this one's done.
The other one won't take me nearly as long so I should be done with them this weekend and on the car next weekend for sure. I'm getting a video camera next weekend too so I can get some sound clips!

[Thrasher]

Here's a picture of the final layout and the first one done with a couple of coats of 1200 degree paint. I started on the second today and it went a lot faster! Will be done with the second tomorrow and they'll be on the car next weekend.

[WickedMom]

uhhh you forgot the inlet and outlet?

[Thrasher]

uhhh you forgot the inlet and outlet?

Lol, I was waiting for that. I don't know exactly where they need to go so that'll be part of putting them on the car.

[BigRed585Lbs]

I thought that was to keep the drone from getting out!

[Thrasher]

I got one of them on the car yesterday, got rid of the washer mod on the other and took it for a spin to check it out. I might be a little biased here, but I think it sounds INFUCKINGCREDABLE!!! With just one on it's a little quieter than the washer mod with a nice smooth flowmasterish sound at idle and cruising, but at WOT it screams and you can really tell the difference the x-pipe made!. For the drone test I took it up a hill with the CC set to 70 and it was no where to be found. :thumbsup: I think with the other installed the sound level should be right where I wanted it. I'll get some sound clips on Saturday and post everything up next week sometime.

[norm8332]

Nice!

cant wait see/hear this.

[Thrasher]

Just to update you all I did not get the second muffler on last weekend. I'm only home once or twice a month right now and I miss my family and friends so I spent the rest of the weekend with them. I'm going home next weekend and will finish her up then.

[Thrasher]

Finally got them done this past Saturday. I would have posted sooner, but it was nice weekend and I spent the whole time driving the crap out of her. Sounds pretty good and a lot quieter than I expected. Here's a quick video of a start up and rev, but of coarse it does the sound no justice. It's a ton less raspy then this reflects and inside the car is quieter than the washer mod.


http://i893.photobucket.com/albums/ac135/tvalade/2008%20G8%20Gt/th_StartUpRev.jpg (http://s893.photobucket.com/albums/ac135/tvalade/2008%20G8%20Gt/?action=view&current=StartUpRev.flv)

[terryscott621]

Link no worky. :-(

[Thrasher]

Damn it. I was trying to embed one and that wouldn't work either. I'll mess with it.

[Thrasher]

Try this...

UPKms6OFSto

[alex94z]

Wow, very nice!

[Aussie]

Thrasher, you have done a good job, well done. There are two other ways to cure the dreaded drone by using a helmholtz reflector chamber. The blank ended J pipe works by being of length 1/4 of a wavelength. It travels "there and back", hence travels 1/2 wavelength and on its return to the exhaust pipe, its "sine" wave is now out of phase with the incoming sound wave and when you add the two together, the resultant wave is cancelled out. The relationship being RPM =Frequency *60/4. The 60 is to get the minutes converted to seconds, and the 4 is because there are 4 spark plug firings each rev. Hence RPM =Freq * 15. The drone revs seem to be around 1800 rpm, hence a frequency of 1800/15 = 120 hertz.

Wavelength = Speed of sound/Freq. The sound speed varies with temperature, hence is a bit hard to calculate precisely. The muffler gas is at about 50c, not all that hot really and speed of sound in exhaust gas at 50c is 1180 ft/sec. As a comparison, at 100c, C = 1235 ft/sec. Wavelength is 1180/120 = 9.83 feet. A J pipe needs to be 1/4 of a wavelength long, hence around 2.46 ft = 29 inches. It can vary a bit from this length because it will still work over a small range as the reflected sine wave will reduce the height of the incoming wave. It seems to work over a 300 rpm range.

The other options to build a helmholtz chamber are common to those who play a guitar. The chamber has a hole for the sound to enter, that hole is a certain length, and enters a box of a certain volume. Sound enters the hole and is reflected back such that it can either add to , or decrease a note of a certain frequency. Hence a muffler can also have a box that samples a sound wave using a tube of length L and diameter d, entering a box of volume V at a speed of C . By using the correct sizing, the aim is to get the reflected pulse to be half a wavelength out of phase, the same as the J pipe achieves.

The magic formula to design a helmholtz chamber to fit inside a muffler body is:

Freq = C/2pi * [A/(V*(L+.8d))]^.5. This is for units in ft. If you use c=1180 ft/sec and inches for dimensions for the entrance tube of A, length L and diameter d, and box dimensions to get a volume V in inches3, then multiply the formula by 12.

Try this to cure drone at 1800 rpm as a first trial: Box size: 6" * 4" * 4" V = 96 Tube to pass the sound wave 1" long tube of 3/4" diameter, has A=0.4418. Use C= 1180. Freq = 12 * 1180/2pi * [.4418/(96*(1+.8*.75))]^0.5 = 126 hertz = 126 * 15 = 1897 RPM. Fairly close and would work over a range of 1700 to 2000 rpm.

The other option is to build the same helmholtz chamber but instead of putting it inside the muffler body, it can be part of the exhaust pipe. It looks like a "hotdog" and if you look at a standard G8, you will see one under the gearbox. Same as the chamber, it has a large pipe, about 4" diameter welded over the existing exhaust pipe. The exhaust pipe has a hole drilled in it of diameter d, and length L where the L is really the thickness of the exhaust pipe. Try a "hotdog" of 4" OD fitting over a 2.5" exhaust pipe, with the hotdog being 4" long and the hole size drilled to 1" diameter. The length of the hole is 1/16" inch, the thickness of the ex pipe. Work out the "annulus" volume, meaning the volume of the air space between the two pipes, V = 27.5 in3 Plugging this into the same formula above, gives freq = 124, and RPM is 1857. This quite small "hotdog" would fit easily on any straight pipe length but works best closer to the muffer end. Building several sizes would give a wider rev range to improve effectiveness.

A simple speadsheet allows you to play around with dimensions. If you look inside a Magnaflow or Flowmaster you will see they use the Helmholtz chambers decribed above. Corsa uses the 1/4 wavelength approach by having several sealed tiny tubes of various lengths to give a wider range of revs to fix the horrible drone issues.

I hope this info helps.

[-Ray-]

Nice 1st post. We actually have a helmholtz thread. :) You've added some very useful information to that.

[Thrasher]

Thrasher, you have done a good job, well done. There are two other ways to cure the dreaded drone by using a helmholtz reflector chamber. The blank ended J pipe works by being of length 1/4 of a wavelength. It travels "there and back", hence travels 1/2 wavelength and on its return to the exhaust pipe, its "sine" wave is now out of phase with the incoming sound wave and when you add the two together, the resultant wave is cancelled out. The relationship being RPM =Frequency *60/4. The 60 is to get the minutes converted to seconds, and the 4 is because there are 4 spark plug firings each rev. Hence RPM =Freq * 15. The drone revs seem to be around 1800 rpm, hence a frequency of 1800/15 = 120 hertz.

Wavelength = Speed of sound/Freq. The sound speed varies with temperature, hence is a bit hard to calculate precisely. The muffler gas is at about 50c, not all that hot really and speed of sound in exhaust gas at 50c is 1180 ft/sec. As a comparison, at 100c, C = 1235 ft/sec. Wavelength is 1180/120 = 9.83 feet. A J pipe needs to be 1/4 of a wavelength long, hence around 2.46 ft = 29 inches. It can vary a bit from this length because it will still work over a small range as the reflected sine wave will reduce the height of the incoming wave. It seems to work over a 300 rpm range.

The other options to build a helmholtz chamber are common to those who play a guitar. The chamber has a hole for the sound to enter, that hole is a certain length, and enters a box of a certain volume. Sound enters the hole and is reflected back such that it can either add to , or decrease a note of a certain frequency. Hence a muffler can also have a box that samples a sound wave using a tube of length L and diameter d, entering a box of volume V at a speed of C . By using the correct sizing, the aim is to get the reflected pulse to be half a wavelength out of phase, the same as the J pipe achieves.

The magic formula to design a helmholtz chamber to fit inside a muffler body is:

Freq = C/2pi * [A/(V*(L+.8d))]^.5. This is for units in ft. If you use c=1180 ft/sec and inches for dimensions for the entrance tube of A, length L and diameter d, and box dimensions to get a volume V in inches3, then multiply the formula by 12.

Try this to cure drone at 1800 rpm as a first trial: Box size: 6" * 4" * 4" V = 96 Tube to pass the sound wave 1" long tube of 3/4" diameter, has A=0.4418. Use C= 1180. Freq = 12 * 1180/2pi * [.4418/(96*(1+.8*.75))]^0.5 = 126 hertz = 126 * 15 = 1897 RPM. Fairly close and would work over a range of 1700 to 2000 rpm.

The other option is to build the same helmholtz chamber but instead of putting it inside the muffler body, it can be part of the exhaust pipe. It looks like a "hotdog" and if you look at a standard G8, you will see one under the gearbox. Same as the chamber, it has a large pipe, about 4" diameter welded over the existing exhaust pipe. The exhaust pipe has a hole drilled in it of diameter d, and length L where the L is really the thickness of the exhaust pipe. Try a "hotdog" of 4" OD fitting over a 2.5" exhaust pipe, with the hotdog being 4" long and the hole size drilled to 1" diameter. The length of the hole is 1/16" inch, the thickness of the ex pipe. Work out the "annulus" volume, meaning the volume of the air space between the two pipes, V = 27.5 in3 Plugging this into the same formula above, gives freq = 124, and RPM is 1857. This quite small "hotdog" would fit easily on any straight pipe length but works best closer to the muffer end. Building several sizes would give a wider rev range to improve effectiveness.

A simple speadsheet allows you to play around with dimensions. If you look inside a Magnaflow or Flowmaster you will see they use the Helmholtz chambers decribed above. Corsa uses the 1/4 wavelength approach by having several sealed tiny tubes of various lengths to give a wider range of revs to fix the horrible drone issues.

I hope this info helps.
Holy crap, good info Aussi! Thanks.

[Filterman]

Aussie, Do you need to alter the calculations to account for the AFM dropping 2 of the cylinder pulses each RPM when active ?

[Thrasher]

Aussie, Do you need to alter the calculations to account for the AFM dropping 2 of the cylinder pulses each RPM when active ?

Ray is right. These questions and info, albeit very interesting and useful, are better suited for the original Helmholtz thread for others to view and use.

[Aussie]

The reduction to 4 cylinders does change the arithmetic because instead of 4 sparks per rev, there will be 2 sparks. Hence the J pipe size is twice as long, and if you use the chamber style, then the dimensions change. I have driven one of these cars for thousands of miles and think they are a waste of time in 4 cylinder mode ... the amount of time you are actually in 4 cylinder mode is minimal. When you barely touch the accelerator it jumps back to V8 mode. However, a suitable chamber would still fit inside a flow through muffler.

It is hard to find the correct formula for Helmholtz chambers, hence I believe my post it is better kept in this thread. The J pipe solution is a stand alone solution for people who have purchased muffles that still drone. If you are building your own mufflers, it is a good solution to incorporate the chamber inside the muffler. Australian experience is that the rear mufflers are for sound only as there is not much power to gain with a straight through muffer ... it is all about the sound achieved.

[BigRed585Lbs]

Thrasher, it's been a while, and you've had time to build up some carbon, so what's the verdict on "your" mufflers?

[Thrasher]

[QUOTE=BigRed585Lbs;250273]Thrasher, it's been a while, and you've had time to build up some carbon, so what's the verdict on "your" mufflers?[/QUOTE

Too quiet for my taste, but Wifey likes it and I'll admit it's nice on long drives with no drone. Kinda funny that last week I was swearing up and down that it sounded like it got quieter, but she said I was crazy and just hadn't driven it in a while. The carbon build up makes perfect sense. They still sound good and are perfect for a family car, but I'm counting the days till it's no longer a family car and the Super-44's go on with headers and hi-flow cats.

[BigRed585Lbs]

Well, the project didn't end up thrown into the dumpster, like so many experiments. You went all the way to completion and actually made something that canceled out the drone. I'd call that successful, and congratulate you. Good job. Now, how about a "washer mod" for a little more sound? (Always leads to this, huh?)

[Thrasher]

Thanks BigRed! It amazes me how we all think the same way sometimes! Washer mod went back on for the trip to my office through the twisties last Wednesday to get more pop on downshifts. I don't know, I like the more refined sound of a real axelback as opposed to the washer mod and am seriously considering the Solo Mach Shorty. Might be the best of both worlds for me. Quiet enough for the wife and kids with another on the way, and loud enough for me with the windows down at WOT. Been saving for a Vararam, HSRK and a tune, but I weaseled my way into getting one of my subs to pick all that up for me and it just so happens that the cost of that combo is around the same as the Solo with a GXP diffuser, we'll see. I may just build another set using what I learned from these and have them installed at a muffler shop, that took more time than getting the second muffler welded up. All in all it was a fun little project that came out better than I expected and as you said didn't end up in the dumpster so I guess it was successful.

[tiresmokindad]

Nice one. I think you can do it in your own way. I love to see the results in picture. I will also try to do that muffler on my own. :)

[Thrasher]

Nice one. I think you can do it in your own way. I love to see the results in picture. I will also try to do that muffler on my own. :)

Good luck! PM me if you have any questions or need pointers. I would definately do it a little different next time.

[NVR2FST]

Nice work! I love seeing these DIY project threads. Also, how did you measure your J-bend? Did you run a string up and around right through the middle of the pipe or the short side etc.?

[Thrasher]

Nice work! I love seeing these DIY project threads. Also, how did you measure your J-bend? Did you run a string up and around right through the middle of the pipe or the short side etc.?

Just used a tape measure, but same thing.

[BigRed585Lbs]

Just saw a fellow builder over in the UK. Great minds.........?

http://www.lotuscarlton.co.uk/vxr8ex.htm

[Napalm]

I got all the bits and pieces fabbed up and about half the welding of one done. Damn FedEx didn't deliver, said the address did not exist. That's funny cause I've had 8 or 9 deliveries here from them in the past 2 months. :uhm: Oh well, I wasn't ready for them anyway. These better sound infuckingcredible! They are by no means easy to build with hand tools, an angle grinder and a mig running flux core. I'm taking pictures the whole way through and will post everything and a sound clip when they're on the car. Anyway, here's a sneak peak...

so did you end up putting in a drain hole? is this made of mild steel?

Sorry you had trouble with FedEx. wonder if you had a new driver.