hand mande stainless steel exhaust system.

I'm a metalworker, and my Porter has a very rusty exhaust system.
Before it rots off completely (and I think with LPG exhaust gases in the inside and winter salt on the outside, it can be destroyed in this winter), i want to build a new and hand made system.
I'm not new in these works (I've done some exhaust system for some cars), but I'm new doing it on a three cylinder engine.
I'm feared because I don't want a loud exhaust system.

Basically I want to use the kat from my old Punto, a metallic one with less than 10'000km, connected to the exhaust manifold with a stainless steel flexible pipe, and then to build the silencer with some parts that I recovered and bought after I installed the LPG system.

I have a piece of plate (100mm x 12mm), enough to mill out five flanges, one to connect the system to the manifold, and four to connect the kat to the pipes, about 1.80m of pipe diameter 42.4mm (1-1/4"?) with thickness of 1.5mm, a piece of calendered sheet metal forming a pipe of 180mm with a lenght of about a half metre for the external body of the silencer, made by 1.5mm thick sheet, four discs of sheet metal, worked to fit at the end of the body, some curves and two pieces of perforated sheet that I must bend forming two perforated pipes for the internal noise absorption, all that pieces are in AISI 304 stainless steel.
Basically the idea is to build a silencer (i try to explain by words, in next days I will post some designs) with the central part with perforated tubes, and at the ends of the body I want to build three compression-decompression chambers.
I want to put the kat on the side of the silencer as the original one (I don't know if for the 2wd ones is the same thing, mine is a 4x4 and it have less room for piping), then after the kat the inlet of the silencer is positioned at the rear end of the silencer.
The flow enters in a chamber (between two of the discs, positioned at 50mm distance between them) this chamber is divided in two with another piece of sheet metal), then in the perforated pipe and it reach the second chamber in the front end of the silencer, then it enters the second perforated tube and it arrives in the third chamber (the second half of the first one), then in a non perforated tube, that pass through all the silencer to reach the front end, and it exits from the silencer with a curve and another piece of tube that release the exhaust gases on the side of the van (about at half of the left sliding door).
I hope I was clear...

My question is: I can build a good silencer or (as happened to me with single cylinder engine silencers) it will make a loud noise?

Anyone has worked on that three cylinder?
At now I worked on silencers only for four and six cylinder engines, and on that engines is simple to do a silencer, becouse of the "constant" flow.
The lower the number of cylinders and the greater the difficulty of building it a good silencer...

Well you come across as an engineer

Get your calculator out and some some wave theory...

http://www.enoisecontrol.com/related_articles/engine_exhaust_sound_control_barrier_wall.pdf

and maybe have a think about using this method too, you can make an adjustable one with exhaust clamps and some tube that fits within a tube.

I made a resonator (for power purpose, not as a silencer...) for my old, and heavily powered, moped...that's an exhaust tuned for low-mid rev, I mount on it when I go to mountain.



I stop tuning it when I'm 27, I tought it is difficult to explain that I'm a "normal" man if I were stopped by police with a moped that reaches over 130km/h (in Italy, mopeds can't legally go faster than 45km/h... ).

I sold it to a my friend in 2008...but without the resonator exhaust, I mounted on it an old (and tuned for high rev.) "Giannelli Spitfire" exhaust.

However...
This is my project.
I have made a silencer with only one chamber and two absorption pipe for my old Seat Ibiza about twelve years ago, I want a "not so loud" exhaust, then I added the chamber...And I made a "too silent" exhaust...it "sounds" less than the original one...

In this design there are three chambers...

Exhaust gases enters by the tube numbered with "1" in the first chamber, then enters in the "2", then in "3" and, incredibly, they exits the silencer passing in the "4" tube (not perforated) .

Assume that the silencer ends are transparent, the sectional view shows the pipe offsets (I'm not a good designer).

The tubes, in the resonation chamber, in the design are longer than in the reality, only for clarity purposes on the design...and in the central part, I put some stainless steel scouring pads around the perforated tubes and some exhaust grade fiberglass to fill all the silencer. (stainless steel scouring pads works perfectly to avoid fiberglass panels to be destroyed by vibration of the flow and caked with carbon, I've used it after I discovered a carbonized fiberglass in one of the first silencer I made)



If it is too loud, I can add a resonator (I have room for it on the final pipe, I can add it under the kat).

What do you think of the design?

the design is a simple mechanical baffle and works well on a single cylinder to deaden the noise so sould work on a multi cylinder.

Yesterday I start the work.

I milled two of the three new flanges I need from a triangle cutted out from a 12mm thick stainless plate.

A hard work for my mini mill, but using the right tool, a new IZAR branded 14mm 5flute roughing mill that I bought as "surplus" tool from e-bay, it worked fine.

I'm happy of my chinese mini mill with D.I.Y. enginereed "powertrain"...

In next days I work out the third flange to connect all the system to the exhaust manifold, then I start welding pieces togheter...

Today I milled the third flange out from the 12mm plate.
I also decided to use the old stainless flexble pipe from my Punto, that it have less than 10'000km, but it has a diameter of 60mm.
Then I decided to use two conical section to connect it to the system.

El_Ventu wrote: old stainless flexble pipe from my Punto, that it have less than 10'000km, but it has a diameter of 60mm.

Is that a standard fitment on Punto's? If so do you know what years as I have been after a Flexi for my car exhaust.

rich the mechanic wrote:

El_Ventu wrote: old stainless flexble pipe from my Punto, that it have less than 10'000km, but it has a diameter of 60mm.

Is that a standard fitment on Punto's? If so do you know what years as I have been after a Flexi for my car exhaust.

No, I bought it on e-bay.de for a few money, mine is like this.

You can find a lot of stainless steel flexi searching "edelstahl felexrohr".

The Punto (mine was a 1.7TD) has a not stainless steel flexi.

Here for a stainless one I must pay over 100€...

Ta I will have a search for that it is exactly what I want so I can let the engine move but mount the exhaust more rigidly and closer to the floor pan for clearence.

Some pics


Some parts (the external pipe has to be cutted in lenght):


Milling the hole:


The flange (manifold side) with the cone to reach the d 60mm for the flexi:


Two flanges coupled with graphite gasket, this one I use between kat and silencer:


And this is an idea of how the exhaust from the kat enter in the silencer:


This is the flexi on the kat (old photo, this is the Punto model ):

Today I worked on the silencer.
I made the two perforated pipes out from a perforated stailness sheet, 1.5mm thickness.
Then I wrap around it the stainless scouring pads.





This is the inside.


And this is the silencer.
I must weld the two ends.

It is almost finished!

Today I taken off the old exhaust system, and I started to put the parts (that I have locked togheter with tiny welding points) on the van.

The first part that I finished is obviously the primary pipe.



After that, I had the hands very dirty, I took only a photo of the system mounted, after washing it...



Tomorrow I have to take off it another time, because I must weld on it the terminal pipe in the right position, and weld also the exit curve (at now the exit pipe that pass through the silencer it isn't blocked, I leave it free of moving to be perfectly placed and welded at the end of the work).
I see also there are a few leaks on the weldings..It is very clear where there are leaks, because the kat I used was of my old Punto, turbodiesel, and it is coated with some soot...

Starting the Porter from cold released a lot of water, that mixed with the soot, has marked clearly all the leaking parts
It have a little more noisy sound, more sporty (before it seems it have asthma, now it is a growl), but the "volume" isn't annoying.
Tomorrow, when the welding are finished and the terminal pipe is mounted, I think the noise can be a little lower, because at now from the second resonation chamber, where the pipe exits the silencer, there is a little space and some gases can flow through.

Nice work dude, this must have taken alot of time.

What are you using to weld the stainless steel?

This is going to be the most highly engineered hijet exhaust around.

Thank you!
Except the "parts" (I milled out from a square sheet the four discs, all the flanges, the external tube I founded casually in a small workshop as "scrap") all the work was made between today and yesterday, about 6-7hours a day included bending the perforated sheets in tubes (a shitty job on 1.5mm stainless...).

For welding I use a small MIG welder, a Telwin bimax 132 turbo, with argon-CO2 86%-14% shield gas.

It's a small welder good for DIY works...but it has a good value for money.

I must buy a professional pressure reducer and a 5kg professional gas cylinder for rent...
With DIY throw-away gas cylinder I spent over 30€ only of gas for this work...

Yes those little gas bottles are a waste of time and money.

I just use CO2 in my mig, I buy it at a caravan shop and they don't charge me any deposit on the cylinder. It is not great to weld with, but I don't weld anyway, I just get my dad to come round and weld for me. He is great with a mig, I am rubbish.

But I am interested in welding Stainless steel with a MIG welder, did you use special wire or anything?

You must use stainless steel wire and the proper shield gas, Ar-Co2 mix or better Ar-Co2-O2 mix, or pure argon for good looking welding with not best resistance.
Welding with CO2 makes a poor welding and is difficult to do, welding with mild steel wire on stainless is possible, but welding is made by mild steel, then it has the same charachteristic of mild steel.
Also if made of mild steel, the weld is less rust-resistant, especially in aggressive enviroments, than welding on mild steel, because of anodic oxidation.

Finished!
It's incredible how hotter are EGT in an Otto engine compared to the Diesel...

On my old punto, even with turbo pressure 1.9bar and the injection rate raised to the maximum of the injection pump, I can reach no more than 880°C, at speeds of 90-120km/h EGT was about 380-430°C.
On the porter I read 650° at about 70-80km/h and up to 750 on slightly slope road.

On LPG temperatures was lower than with petrol.
And accelerating a little to disconnect the cut-off, in engine braking, from the exhaust comes little "pops" about only when running on petrol...then the combustion on LPG stays in the cylinder, no matters what I read on VSR...

That's a right cheeky exhaust system mate! I love the side exit pipe. You'd done good there.

I love side exit too, I hope that Officiers don't hate it...

No changes in sound, that's perfect!

the exhaust passed the winter with no problems...but at now it's totally darkened by temperatures...

No changes in sound, for now.

thats some nice work youve done there   

Thank you!