Exhaust Build Advice

[madpugger]

Hi guys,

I am just away to get an exhaust made soon for the CT355 and was wandering if there is anything I have missed that I should consider.

I was thinking of having it somewhat modular, in that I could insert an additional silencer, swap out the CAT etc.

So, thoughts were.

3" DP with V Band, 2x threaded nipples for EGT and WBO2.
A braided flexi just after the bend below the subframe
A V Band? or an audi type sleeve? just after that.
A CAT or CAT removal pipe.
A V Band? or audi type sleeve?
Centre Section with? or without? silencer.
Rear box

Also a seperate wastegate screamer pipe.
All the way to the rear?
Will it need a silencer?
1.5" enough?

TIA
Mike

[Rusty]

100cpi sports cat shouldn't need swapping out really.

Having an extra silencer should be a good idea on a straight through 3" system, they can resonate. Another option is to have a piece of pipe that can be replaced with 2.5" such that it damps the standing waves a little, this might not be suitable for full boost but might be much nicer for daily duties.

[Lloyd]

Worth having a look at Chris Tullet's site for the parts to make your own exhaust.

Andy - I now get a little bit of resonance with the new 3" straight through system.
I called and spoke to one of the engineers at Tullets and he suggested that as the overall sound levels were OK, I didn't need an additional silencer and that the resonance was due to the newer, free floating and thinner exhaust piping 'humming like a guitar string'.

He suggested we damp it down by adding an additional fixing point somewhere along the free floating section. Made sense as we had done away with the original exhaust mounts at the bottom of the DP by the cats. I will report back to confirm if putting back the mounting point solves the resonance.

[DamianURS4]

thats interesting - I have a 3" straight through and have suffered with the same - did away with the OEM mounts - so will be keen to learn from your findings.....

[madpugger]

100cpi sports cat shouldn't need swapping out really.

Having an extra silencer should be a good idea on a straight through 3" system, they can resonate. Another option is to have a piece of pipe that can be replaced with 2.5" such that it damps the standing waves a little, this might not be suitable for full boost but might be much nicer for daily duties.

I was thinking more like any cat for a MOT and no cat for the "Track " although I had also thought of a race type cat of 200cpi. I'd rather have a CAT I KNOW will pass an mot than one that MAY not if you get my drift. Also I have a choice of 4 ramps to put it up on, so an easy swap option is not such a pain as if I was doing it laying on my back in the rain!

Interesting point about the wall thickness, are there other options to stainless that are affordable/any use? Are there wall thickness options of 3" stainless?

[Lloyd]

Have a look here:
http://www.christullettexhausts.com/...pipe-bends.asp

[s2_wot]

If you take a look at the back box design off the coupe in this thread you'll see that it's very free flowing and effective:

http://www.s2forum.com/forum/showthread.php?t=49180

It's way more efficient because in total the gasses turn through 90 deg + 90 deg whereas a lot of the aftermarket ones turn 90 + 180 + 90 as is the case with the milltek and jetex ones IIRC.
By turning the gasses 90 deg inside the silencer the soundwaves are continuing into the silencer media.

With the straight through designs there isn't a great opportunity for the soundwaves to be taken into the silencer media as the wavelength is about 8m long. For this reason my preference is for the gasses to turn 90 deg within the silencer.

Terrybullwon told me before that a lot of the v band rings you can buy are made from cast material and will crack when welded and you'd be better to have ones that were machined from bar. Repo has mild steel ones available and prefers them to stainless.

This guy will give you a good price for the sports cat and ship it to your door if you ask nicely.

davidc@bmcatalysts.co.uk I can't find his phone number at the moment, though it's probably on the website. BMU38/304 is the part number for a 3" 100CPSI Metallic cat.

Another company worth a google is Western Tydens.

Wagner say there is no need to use a flexi section in the DP for their cast manifolds however for peace of mind I'd use one or two in the exhaust. 3" pieces are relatively easy to get.

[madpugger]

If you take a look at the back box design off the coupe in this thread you'll see that it's very free flowing and effective:

http://www.s2forum.com/forum/showthread.php?t=49180

It's way more efficient because in total the gasses turn through 90 deg + 90 deg whereas a lot of the aftermarket ones turn 90 + 180 + 90 as is the case with the milltek and jetex ones IIRC.
By turning the gasses 90 deg inside the silencer the soundwaves are continuing into the silencer media.

With the straight through designs there isn't a great opportunity for the soundwaves to be taken into the silencer media as the wavelength is about 8m long. For this reason my preference is for the gasses to turn 90 deg within the silencer.

Terrybullwon told me before that a lot of the v band rings you can buy are made from cast material and will crack when welded and you'd be better to have ones that were machined from bar. Repo has mild steel ones available and prefers them to stainless.

This guy will give you a good price for the sports cat and ship it to your door if you ask nicely.

davidc@bmcatalysts.co.uk I can't find his phone number at the moment, though it's probably on the website. BMU38/304 is the part number for a 3" 100CPSI Metallic cat.

Another company worth a google is Western Tydens.

Wagner say there is no need to use a flexi section in the DP for their cast manifolds however for peace of mind I'd use one or two in the exhaust. 3" pieces are relatively easy to get.

Cheers guys,

Trouble is there is no room to put a coupe style back box on for the spare wheel well. The Avant system is completely different, it goes under the axle, not over, and all silencers are in line with the car.

I already have a few stainless V Band flanges, one of which is from Repo Same goes for the flexi, its sat here. I want to use it as my exhaust hits the ground a lot where i stay and I would rather the EM and Turbo did not have to take the pounding

I will look into the CAT issue, but think I'd like a 200cpi...

Cheers for the info so far folks

[Lloyd]

Terrybullwon told me before that a lot of the v band rings you can buy are made from cast material and will crack when welded and you'd be better to have ones that were machined from bar. Repo has mild steel ones available and prefers them to stainless.

Wagner say there is no need to use a flexi section in the DP for their cast manifolds however for peace of mind I'd use one or two in the exhaust. 3" pieces are relatively easy to get.

V-Band are top quality from Tullets. They have a male/female design which helps get a good seal and for us at least they didn't crack or warp on welding.

I bought a 4" flexi with the aim of locating it at the bottom of the DP. In the end we didn't fit it as there was no space due to the subframe. I called and spoke to Milltek to ask about their original RS2 3" DP turbo back design - they didn't use a flexi.

[madpugger]

V-Band are top quality from Tullets. They have a male/female design which helps get a good seal and for us at least they didn't crack or warp on welding.

I bought a 4" flexi with the aim of locating it at the bottom of the DP. In the end we didn't fit it as there was no space due to the subframe. I called and spoke to Milltek to ask about their original RS2 3" DP turbo back design - they didn't use a flexi.

do you mean a 4" long, 3" dia flexi? I really would prefer one as like I say, it hits the ground here a LOT.

[Lloyd]

Yes, a 3" diameter, 4" long flexi

[s2_wot]

Cheers guys,

Trouble is there is no room to put a coupe style back box on for the spare wheel well. The Avant system is completely different, it goes under the axle, not over, and all silencers are in line with the car.

I already have a few stainless V Band flanges, one of which is from Repo Same goes for the flexi, its sat here. I want to use it as my exhaust hits the ground a lot where i stay and I would rather the EM and Turbo did not have to take the pounding

I will look into the CAT issue, but think I'd like a 200cpi...

Cheers for the info so far folks

If your avant system is going in the bin I'd love to see a few shots of the insides of the back box. Do you have an angle grinder?

I bet it's resonated also the same as the coupe one, something else you won't find too easy off the shelf.

EDIT: Maybe you would consider an ovalised section there at the gearbox / subframe for improved clearance. The guy with the ur quattro (hamish I think) did a really nice job of the ovalised bend in that area.

[madpugger]

If your avant system is going in the bin I'd love to see a few shots of the insides of the back box. Do you have an angle grinder?

I bet it's resonated also the same as the coupe one, something else you won't find too easy off the shelf.

EDIT: Maybe you would consider an ovalised section there at the gearbox / subframe for improved clearance. The guy with the ur quattro (hamish I think) did a really nice job of the ovalised bend in that area.

The std system and the Supersprint ones will both be for sale im afraid

Ovalised could be an idea, or two 2.5 sections...

[Bram]

check my project thread for ideas and all details:

http://www.s2forum.com/forum/showpost.php?p=440899&postcount=311

My avant ran a 1" screamer and 3" exhaust. Should be sufficient for the CT355.

[s2_wot]

The std system and the Supersprint ones will both be for sale im afraid

Ovalised could be an idea, or two 2.5 sections...

A lot of the ovalised stuff (burns stainless in the US) on the market is made to have the same circumference as the round pipe but to avoid creating a bottleneck you need to look at the cross sectional area.

76mm SS Tube 1.5mm Wall Internal Area = 4193 sq mm

3" Oval is made from a 53mm Tube thats split and put back together with an outside dimmension of 88.9mm. With a 1.5mm Wall; Internal Area = 3706 sq mm

A better oval would be made from 60.3 Tube and an outside dimmension of 88.9mm giving an Internal Area = 4121 sq mm

Making the transitions is the pain but an extra 15-20mm ground clearance can be gained in that area.