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Since a full exhaust is not at the top of the list for upgrades I decided to build a custom rear muffler. Main goal was to be able to actually hear the exhaust, and not just that unhappy high rpm engine noise, while at the same time not be loud and obnoxious to people outside the car.

Luckily at work we had some scrap stainless steel tubing/sheets/elbows, and a few welders with not much to do.

I started out by making the inner pipe:



It was made with 2.5 inch 314 stainless tubing (sch20), since we didnt have a proper mandrel bending machine the curves were made using 3x 90 degree elbows (sch40), a bit thick but thats I we had.

The flange was by far the hardest part, and it still doesnt sit flush, because the OEM pipe has about 20mm of pipe sticking out of the OEM flange, which doesnt fit well inside this pipe. To make it fit without leaks I am using both the OEM gasket and a graphite high temperature/pressure custom cut gasket (also scraps).

The next step was to decide on how long the actual muffler housing would be, and then I proceeded to drill 8mm holes along the whole length of the pipe.

Unfortunately I didnt get pictures of the holes, but just used a vertical mill and spent about 3 hours drilling them. they are about 6-8mm spaced from each other.
Fair warning: it is a tiring process, and I recommend having some way to keep the exhaust aligned so it doesnt rotate. With stainless steel, take it easy and dont put too much pressure on the drill, keep the drill cool and lubricated, id recommend a brand new drill.

after this, we bent a 1.5mm thick plate into a cylinder with a plate roller(I dont have the diameter, but basically just install the bare pipe into the car and check how much clearance you have to the top trunk heat shield, and then leave 10-20mm).
The plate is a bit too thick and heavy, but it was free :)
I would recommend a 0.5mm plate if you can source it.

The end caps were made of the same sheet, cut with a plasma cutter, and then ground smooth with an angle grinder. Make sure to cut the inner hole a bit smaller, and then use a carbide bit or similar to grind it closer to size.
The plates were then cut in half.

Welded the first end cap in place along with the cylinder.

We had some Ceramic Fiber available so used that, its quite compact and heavy stuff, so I cut it in small chunks and "de-fluffed it" to make it less dense (also improves noise dampening) and proceeded to stuff the cylinder with it.

As with most fibers, wear gloves and a competent breathing mask, as its quite nasty stuff.

I didnt compress the fiber much inside the cylinder and then welded the final end cap in place. Then the final TIG weld was done all over. This ceramic has a very VERY high melting point, so dont worry about fires or even melting. We even tested welding directly on top of a piece of it with maximum current and it did not melt.

Then got some solid stainless bar about 5mm thick, and created the hooks to latch onto the stock rubber mounts, this is a bit trial and error even with measurements, but its fairly easy to hammer stuff into place to tweak it.

To finish, ground out the welds flush, and then brushed the stainless in acid to remove any contamination (acid used a lot to passivate stainless, optional but you might end up with small spots/rust on it afterwards).

In the end polished the stainless to get rid of some scuffs, and test fitted it to the car, adjusting the hooks to get good clearance from the tip to the bumper.



I will try to get more pics whenever im near the car again.

Noise wise, its JUST audible, deep throaty sound, no rasp (not very raspy either even without the rear muffler), there is a very slight drone at 1800-2000rpm.
The intake is actually much louder than the exhaust. Honestly, should have made the muffler section shorter/less diameter but cba now.

Weight wise, its about 2 Kg heavier than stock, due to me using a bit too thick sheeting and WAY too thick 90 degree elbows (schedule 40). But for a basically free exhaust (appart from 2 cases of beer for the welders) cant really complain.

As for power, dont know, dont notice any difference, will have to dyno. It is basically straight through so I assume I did gain something.

(Side note on the ceramic fiber, for the first 1000-2000 Km/miles there will be LOTs of white fibers on your rear bumper until the fiber settles in, nothing to worry about it has completely stopped doing it after 2 or 3 tanks of gas)
 

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looks nice dude :)
i'll be building my system soon.
 

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You know you can buy stainless perf tube for like $40 for 2 feet. Or you can even buy perf sheets for pretty cheap too. I make my muffler cores either by buying the stainless tube or rolling and welding my own aluminum ones for when the exhaust is using aluminum tube.
 

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You know you can buy stainless perf tube for like $40 for 2 feet. Or you can even buy perf sheets for pretty cheap too. I make my muffler cores either by buying the stainless tube or rolling and welding my own aluminum ones for when the exhaust is using aluminum tube.
Yeah, the main point of this was to use whatever scrap we had to keep costs down. If/when I ever make another one (because this one is quite heavy) I will most likely go that route (as well as some thinner everything because this is marginally heavier than stock). Ty for the heads up.



Ill take some video but its quite tame and you hear the intake more :D
 
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