Bengt Sweden

I am about to build myself an exhaust all the way from the turbo including a metal core cat and just one muffler. My intention is to use a double pipe muffler so that the WG can use one of the pipes. I plan to use the existing WG piping and just extend it. I will need to use the integrated WG cat to pass emissions test.

My question are: where to put splits, whether to use a flex pipe, whether or not to attach to the block?

Pictures of your custom exhaust appreciated.

TIA
Bengt

J Chen

Hi Bent,
Heres my 2 cents gathered from my GT install experience.
1. Pipe must go into the flanges before any welding is done.
2. Try to increase the bend from the turbo out cause the bend
on the factory set up is to tight especially from the point of
entry to the turbine housing.
3. I think installing a flex joint from the wastegate dump pipe
to the exhaust is a good idea.
4. You must keep the mounting lugs of the turbo down pipe.
This helps to reduce stress going to the turbo housing.
5. Since you're going to use a wastegate cat, can you not dump
it straight out to the atmo ?

Bengt Sweden

Hi J!
I am not bent, only the piping ;-)
2.Yes, there is room to increase the radius slightly even with 3".
3.the wastegate pipe will go parallel all the way to the final muffler
4. but is it necessary? and should I keep the split in the same place?
5. dumping to atmosphere will not only increase noise too much but also risk heating the underside of the body

Thanx
Bengt

Duke

Since emissions are only checked at idle there will be no flow through the wastegate. So removing the small cat shouldn't cause any problems. Well besides visual inspection but I don't think anyone will actually notice that.

Bengt Sweden

They actually did at last visit and complained about the WG entering after the cat. I had to point at the small cat and explain that it was a stock exhaust. I may be lucky next time but why take a chance?

Bengt

Danno

I built my own 3" one-piece exhaust from the exit of the down-pipe all the way back to the muffer a couple years ago. You don't need bending if you just get U-bends. Cut it up into pie-sliced sections to fit the bends you want and butt-weld to straight tubing. I ended up needed a single 3" U-bend and a 6-foot section of 3" tubing. At the muffler, I have a quick-release slip-fit with springs to hold it on. I can swap for a straight pipe at the track in about 30 seconds.

Bengt Sweden

Thank you for the ideas. I'll post some pictures when I get started. I now plan to use quick fit dairy couplings. This will allow freedom to rotate, same as a slip fit.
cheers
Bengt

J Chen

Hi Bengt,
Why is there a need to connect the wastegate dump pipe
all the way to the final muffler ? Are you worried about
the addition of turbulance as well as back pressure ?

Bengt Sweden

Correct. Porsche is doing this better than most by re-entering after the cat but to not reenter at all of course gives the least negative effects on flow.
Is there a measurable difference? I don't know. I don't have the resources to evaluate different alternatives so I have to resort to common sense or others experience. What is your view? I think this is better than to go for 4" with wasted exhaust gas re-entered.

Bengt

Duke

Someone did a dyno with and without re-enter and gained a few ponies without letting the wastegate enter the regular piping.

BTW, I'm surprised about the picky inspections person!

dhallilama

this will be an interesting post... planning on building my own shortly...

Bengt Sweden

....provided we get some input

I think we need some pictures now

heres a stock exhaust

pete95zhn

Hej Bengt,

what's that muffler-like thing there just after wastegate enter to the main pipe? My car does not have it and my exhaust is original and there's nothing about that in the PET.
BTW,what do you think about RakaRör's "Special"...? http://www.rakaror.o.se/

threesticks1

Hey Bengt: Does your exhaust have two mufflers? Is that what that pear shaped thing is just down stream of the WG by-pass entry? Is the muffler near the tail pipe different from what we have here in the US? I have looked on PET but don't remember seeing anything like that for the European 951s.

J Chen

If that's the case you can give it a try & since it's a
diy project may I suggest that you build it from
aluminium pipes. That will save you lots of weight.
I've got a 951 buddy here that had a custom exhaust
made out of aluminium & it's holding & working out
very nicely but you must use thick gauge pipes to kill
resonance .