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View Full Version : Custom down pipes and De-cat



jayp
28-04-2011, 04:58 PM
Well after Aboo tried to get some down pipes made up in the group buy I decided to look into making my own, I can already weld and with the old down pipes off my dead car all I had to do was knock up a jig and buy some Pipe.
3 weeks later the pipe arrived and I started cutting and welding. The welds aren't overly pretty but they are gas tight and they aren't going to fall apart either!!
I've gone with 2.5 inch from both turbo's to 3 inch after the second with a simplified join from the stock ones, thought about doing a y-pipe but would have had to mock it up on the car, I don't have the facilities for that. the de-cat is 3 inch.
Managed to get the car on the ramps at work last night after everyone else finished to do the final fittings. the pipes are heat wrapped up to the 3inch flexi just in case they fouled on the under tray which I believe was a fault with the RPW ones? but there is no fouling at all, it is a little tight up to the sump but doesn't seem to be causing any problems as yet. I can always do a little fiddling around with that later.
I've got to say the noise is now more of a howl at 4-5000 rpm which is really growing on me and more burbley at idle, but isn't too loud. Turbo spool up is much much faster making the car more responsive all round.

I apologise for the poor quality photos only had my phone with me because I left my camera at home!

4421344214

Wodjno
28-04-2011, 05:02 PM
Nice work /yes
What was a rough cost doing it yourself ?

aboo
28-04-2011, 05:03 PM
What kind of bend have you put in from the back turbo? Its hard to see with it being rapped but it looks quite straight.

Colin Wiltshire
28-04-2011, 05:06 PM
Looks good, only 1 problem I can see is the angle of the join, My limited knowledge would suggest the the exhaust from rear turbo would stall at join, poss trying to go forward untill pushed back from front turbo exhaust, plus might get extra hot at that point.

jayp
28-04-2011, 05:06 PM
It cost about £130 for the pipe and flanges, about £60 worth of gas for the MIG purely because I'm leaving Germany soon and didn't want to get a contract with boc so had to use small disposable bottles. would cost far less with a proper bottle. So probably £200 is all up, but I'm lucky enough to have access to plenty of scrap metal to make jigs and what not.

I was thinking of maybe offering them for sale to the club later in the year when I'm settled in the UK again, but it would be an evening weekend thing. When I have time going back to our School of Electrical and Mechanical Engineering to finish my trade training.

jayp
28-04-2011, 05:14 PM
It's not straight, its a 90 degree mandrel bend with the pipe from the front turbo entering the back of the bend so the gasses from the rear turbo have already started flowing towards the rear as front reaches it. the step up to 3 inch is part of the join. the idea being the combination of both exausts needs the extra cross sectional area.

aboo
28-04-2011, 05:25 PM
It was hard to see with the rap on. Good job/yes

foxdie
28-04-2011, 05:51 PM
Might be onto a money maker here, if you can get the price down to £175-£200, making enough to look after yourself whilst putting out a high quality set of downpipes :)

jayp
28-04-2011, 06:03 PM
Might be onto a money maker here, if you can get the price down to £175-£200, making enough to look after yourself whilst putting out a high quality set of downpipes :)

The thought had crossed my mind, I've got so much help and advice from this club it would be nice to give something back. Its some thing I will look into after my move in July.

TAR
28-04-2011, 09:30 PM
did you create the rear flange so that it will mate up with a standard cat? it looks like you can only have the decat fitted?

Good job on having a go yourself

:happy:

The Vee
28-04-2011, 09:40 PM
Very good! Am currently in the throws of doing one for mine. Have you got another small flexi in there somewhere? ie in the rear turbo downpipe or even between the two? I'd be a little wary of stressing if not.

jayp
28-04-2011, 10:00 PM
did you create the rear flange so that it will mate up with a standard cat? it looks like you can only have the decat fitted?

Good job on having a go yourself

:happy:

yeah the de-cat is identical length and the flanges are identical offset as the standard cat so it will mate up no problems.



Very good! Am currently in the throws of doing one for mine. Have you got another small flexi in there somewhere? ie in the rear turbo downpipe or even between the two? I'd be a little wary of stressing if not.

To be honest I didn't really see much need as this was a one off and if it had not been a good fit between the turbo's, I would have altered the end product. the first short flexi is only really there for manufacturing tolerances as far as I could tell it serves no real purpose as neither turbo can move independently from the other, the longer flexi takes into account the movement in the engine mounts and the rear section of the exhaust. The other reason i didn't use a second flexi on the front pipe was i remember reading a thread a while ago about the RPW pipes grounding out and destroying the flexi very easily. If it were to be mass produced I would say a sliding joint in the same place as the original small flexi would suffice to allow for the different turbo positioning between cars without the bottle neck produced by a 2.5 inch flexi.
I've gotta say there's nothing quite as rewarding as doing a job like this when its complete is good to have the satisfaction its totally unique in some way. If I can be of any help along the way feel free to PM me, and good luck

I would like to point out I'm no exhaust specialist and if I anyone knows differently correct me before I do some serious damage to my car!!!