Wastegate exhaust size

[Keeper of The Kitten]

I'm in the process of getting a new Ø3" exhaust downpipe and shorter system made (found all the tube supplies I need and Wab is due to help with flanges and some other non-exhaust bits), and while I am doing this I intend to separate the wastegate exhaust from the downpipe.

I'm just wondering about the size of the WG exhaust - is there any advantage to larger WG pipe, or would it be problematic to be slightly smaller? If bigger is better then I would gladly increase the size of that pipe.

I am thinking that there is little or no point in being larger than the opening on the EM (which is an RS2 type). Does anyone have any experience or opinion?

Thanks in advance!

__MDC__

[Urquattro20V]

Separating the WG exhaust is a good idea for less restriction, though I would think there's more to be gained by changing the EM. You'll need a new downpipe once you go custom...

That being said, a 2" tube should do the trick. Then you have the choice of letting it join the main exhaust further down, make it go all the way to the back or just directing it straight down!

I know Audi_CQ on here built a pretty wicked exhaust system, he can probably give some pointers.

Here's some inspiration from a familiar engine.

[Jamo]

Think of it the same as the exhaust system, the bigger the more gas you can get out.

Search for Pisobiker and his downpipe. He has measurements of the flange and the bore size in the flange.

[MidnightBlueS2]

IMHO, I would keep the same diameter as stock and still reroute it into the main exhaust...

Why ? Because I tried a seperate WG pipe and it was such an awful sound when it chatters that after living with it for only 2 min, we decided ( exhaust fitter and myself ) that it would be better to route it back into the exhaust....

It's just a hugely loud "BRRAAA" sound that overwrites the great turbo rumbling sound coming from the exhaust when boost kicks in...

I know a lot of people won't agree with me on this one but I just wanted to warn you of the outcome...

David

[Jamo]

I'd agree with you i've heard a couple and they are LOUD but i'm not here to pass judgement

[Jon441cc]

http://videos.streetfire.net/hottestvideos/4/e3911f52-9f7c-4b14-aea3-ad8ef911e61e.htm

Here's some open wastegate pipe action

[Keeper of The Kitten]

Thanks for the thoughts guys!

The plan at this stage is route the main exhaust to exit by the RH rear wheel, and I was (sort of) planning the WG pipe to run out just behind the LH front wheel - but if straight down is ok I am game to do that (I'm not sure about the legal aspect of any exhaust gases exiting underneath the car, I was assuming it all had to exit outside the boundary of the body).

It's not the sound that concerns me really, and I am willing to run it separate for a start and consider joining it up at a later date if I deem it to be necessary. As for a custom EM, it's not on the list at this time - I have two RS2 pieces and I am going to fit the brand new one to the present engine combination. There may be a different combination in the future, perhaps looking towards a possible 500bhp project - then I will be looking at custom EM!

I contacted Pisobiker some time ago about DP, and looked at his thread and the pictures. I have designed my own DP flange by referring to the Pisobiker design, and my own measurements from the turbo (hotside is K26 with #6) - I've made a 12° cone that starts in the flange itself, this will run into a 14swg rolled cone before going into Ø3"x16swg tube (SS 304 for the bends and the straight pipe sections, now I've found someone who can supply it). This (DP and system) will be made here at work by an extremely competent race car fabricator (he's done a few exhausts in his time).

I'll see what other sizes the stainless supplier can get me in SS 304!

Thanks again folks, I'll keep you posted on the way this DP works out. It's not coming yet, but it will be coming...

__MDC__

[Sweeper]

Midnight: I also have a strange sound and i think it's becouse of thinkness and size of westegate pipe , but Jeffer friend told me it's mostly becouse of week westegate spring that let's gasses out all the time and not on the gear changes.

Must be it.

[Audi_CQ]

Here's my setup :
It's 3,5" DP with 2" WG pipe into 2*2,5" into 3" over rear. Singel 3" box at the back with dual 2,5" outlets. Made this way to avoid long big pipes that causes resonanse sound. Everyday use with OK noise level

[Keeper of The Kitten]

It definitely looks exciting!

I would look at running the WG pipe joined into the system further downstream, but I am avoiding splitting into two pipes after much thought and advice about the gas disturbance of a split and the further reduction of cross section that more boundary layer causes.

(I was planning to run two pipes to the rear at one stage, with two silencers)

I am doing this with the best theoretical practice I can think of, but it is still "finger in the wind" to a certain degree. The system I have in mind is intended to be kept fairly short since I have concluded that it is less complex and lighter that way, as well as less restrictive than curling over the rear drivetrain.

I thought about going under the rear - but it would end up looking like every Skyline and RX7 with the low hanging pipe, so I now feel the short system is the way I want to go. The underslung pipe would probably be a little straighter, but my plans would still be less convoluted than the present Scorpion system.

__MDC__

[S2central.net]

martin - good stuff... I for one would like to see pics of the eventual system - especially given the background of its fabricator !

The sound of the separate WG pipe is a bit fartty at part throttle, but I still get chills up my spine with memories of the sound that MarkH's car makes at full chat... you would swear blind there is an S1 in the neighbourhood. Its just an awesome noise then which to me makes up for the phartty part throttle noises.

Paul

[Keeper of The Kitten]

Lol it might depend on how much I bribe the guy!

The fabbies at work were always fairly handy - one of them used to challenge himself to weld around an aluminium drink can without blowing a hole in it, which he says he can almost do (apparently).

It sounds like I will definitely start with the separate pipe setup - I'm not good at part throttle driving!!!

__MDC__

[Audi_CQ]

It definitely looks exciting!

I would look at running the WG pipe joined into the system further downstream, but I am avoiding splitting into two pipes after much thought and advice about the gas disturbance of a split and the further reduction of cross section that more boundary layer causes.
(I was planning to run two pipes to the rear at one stage, with two silencers)
I am doing this with the best theoretical practice I can think of, but it is still "finger in the wind" to a certain degree. The system I have in mind is intended to be kept fairly short since I have concluded that it is less complex and lighter that way, as well as less restrictive than curling over the rear drivetrain.
I thought about going under the rear - but it would end up looking like every Skyline and RX7 with the low hanging pipe, so I now feel the short system is the way I want to go. The underslung pipe would probably be a little straighter, but my plans would still be less convoluted than the present Scorpion system.
__MDC__

If "race" system is your goal then a single large bore is OK, but if you want to use it daily then this twin-pipe system works great. So far I've pushed 450+ whp through it and 201 km/h 1/4 mile speed(1650kg with 2 persons in car), so it's not that restrictive

[Ross]

martin - good stuff... I for one would like to see pics of the eventual system - especially given the background of its fabricator !

The sound of the separate WG pipe is a bit fartty at part throttle, but I still get chills up my spine with memories of the sound that MarkH's car makes at full chat... you would swear blind there is an S1 in the neighbourhood. Its just an awesome noise then which to me makes up for the phartty part throttle noises.

Paul

As one who ran a separate WG pipe for a while (pointing to the ground), I can tell you it's pretty loud! Most people don't like it, and it could be a bit noisey at it times - especially at part-throttle as Paul says, it sounds pretty crap. But... I still miss opening her up in 3rd through some narrow, wooded roads and hearing that 5-cyl sound pouring out before it has time to get molested by the turbo... with the windows down of course It had the same effect through narrow streets with tall buildings either side @ night, but I don't think the locals appreciat it

[Billman]

then maybe a Downpipe with a system like this could be the answer. You can open it to the outside on demand.

http://www.atpturbo.com/root/releases/release091004.htm

I think someone here in the Forum made something like this but i cant recall who it was and where the post is.