How to make your own Turbo back downpipe

[Pisobiker]

(or at least here is how I did mine.....)

Having had some requests on how I did manage the building of the downpipe from some DIY guys here in the forum, and since there is no secret at all in what I did (and I'm really not making big money with the few I might build for others), here is the "how to" (my way, of course )

here are some pics

[Pisobiker]

comparison with OEM RS2 downpipe:

[Pisobiker]

My starting points where:

- Pipe having about same route as OEM S2-RS2 one, so to be used with S2-RS2 EM and K24-K24 7200 turbochargers, in the 66mm and/or 72mm ID dimensions;
- Maximized flow with gentle divergent cone from turbine outlet to downpipe ID size and well merged and smoothed out WG pipe to main pipe merging;
- Getting down towards the back of the car with a single pipe, eliminating splitter and double cat line;
- 2mm thick SS piping which, in this case, works great with the easy to find #304 SS.

First problem is Turbine outlet flange and WG flange.
I found a Company who lasercuts them, but had to make a minimum of 10 pieces each to keep prices resonable.
I made them out of 10mm thick SS.
Following are the drawings:

Turbo to downpipe

[Pisobiker]

WG to downpipe

[Pisobiker]

I don't have blueprints and mesurements of the parts because I have built a sort of "template" (using OEM RS2 downpipe). I then cut pipe and bends while assembling them:

[Pisobiker]

Showed in previous picture is last pipe I've built, which was asked to be without WG merging.
I use the showed die grinder and tools to smooth out and polish joints and mergings. Consider a good cutter (in the range of 15-20 euros) will be good for only one pipe: SS is very tough to cut and there is a lot of work to be done in the turbo flange-to-cone area and WG-to-downpipe merging.
The cone is about 50-55mm long and its function is to increase duct section from 58mm (turbine outlet) to the 66-72 mm final size fast enaugh, without causing significant turbulences.
WG pipe is Ø 42mm ID.
I usually start the building from the turbo flange. Before welding the piece (whether it is a straight or a curved piece) I smooth and deburr each side of it, then weld it, cut and polish internal joints before adding following piece.

I don't have a TIG welder therefore using an inverter type electrode welding machine. I use high quality #308 SS electrodes (there are cheaper ones, but high quality electrodes make welding much easier).
I'm not a professional welder, and I'm aware my welds don't look that good, but they are strong and reliable, apart from the fact I put much more effort on the internal smoothness than the outside look.

Some numbers:

in my ~370 Hp RS2 setup the full 3" turbo back system with racing cat converter made me gain 20 hp at peak hp rpm, with gains over OEM system starting from 3500 rpm on. Turbine spool up time seemed improved to me as well, while off boost low rpm pick up worstened a little.... as it's supposed to .

IMHO good ID exhaust sizes for various engine outputs could be:

- Ø 62mm up to 310 hp;
- Ø 66mm up to 360 hp;
- Ø 72mm up to 430 hp;
- Ø 76mm up to 480 hp;
- Ø 85mm up to 600 hp;
- Ø 95mm up to 800 hp;
........


Have fun


Marco

[Dutch_RsBlueS2]

I'm not a professional welder, and I'm aware my welds don't look that good, but they are strong and reliable, apart from the fact I put much more effort on the internal smoothness than the outside look.

Marco stop saying that !

For welding with a stick youre doing an exelent job, yes its possible to get a cleaner weld with tig coz you dont have all the slatters around but for welding with the stick you get a 9+ it looks quite nice.

And you`ve done some exelent job with that selfmade mall ! and also given me some ideas i didnt thought about.

Thnx for this howto ! I`m also making a lot of pictures of my project and will put them on a site when its finished.

Cheers,

Cees

[MikQuattro]

Darn nice guide Marco! Very nice....

[91_S2]

Marco,

You are always very generous sharing information with this list. I can't weld, but I appreciate the gesture

[Pisobiker]

Thanks for the appreciation guys.
This kind of things are just my attempt in giving a contribution to this forum.
I'm just one of the many people here who has found this forum to be an extremely valuable media not only for technical informations but also for a good and healty friendship with other enthusiasts. Sharing infos and knowledge is one of the main points that make this forum the best I've ever seen around.




Marco

[audiman]

Nice one Marco, i think that your time and effort have been well worth the effort. It nice to see a person making something that tuning ppl seem to make a ot of money from.

Just a thought, how about making it from 316 SS for longer durability??? 304 is good, but everything can be improved Nice work BTW, your welding is good for a non-pro

[S2central.net]

Marco - superb stuff ! You are a credit to the group sir !

[Fat Audi 80]

Marco - superb stuff ! You are a credit to the group sir !

Respect to that stick welding. Very impressive for DIY IMO.

Good work.

Cheers,

Steve.

[s2driveruk]

Looks great, top guide and pics...shame i can't weld or i'd have given it a go! Quick question, how easy would it be to have the option of either a separate w/gate exhaust for when you want to use it and then just replace the normal tube section for 'quiet' driving? I 'Guess' (using the word heavily) that you could bolt on a cover on the d/pipe when you are using the external w/gate pipe but no idea if thats practical/possible.

Cheers,

David

[raymor]

Thanks for that Marco. The sharing of you're hard earned work and experience is very much appreciated.

I agree that you should stop belittling your welding ability.... the welds look strong, flowing and neat.... it's just the splatter that deceiving the look of it all.

It's given me a good head start and a time saving that gives me a chance of being able to make my own.

Thanks again,

Raymond