what's the exhaust pipe size should be for GT2871R??

[popdemonic]

I'm hesistating on going with 2.5"X2 dual pipes or just single 3" pipe for the exhaust system on my UrS6 Auto Tranny?I'm expecting the better spool up on the Turbo as my car is auto tranny.I'd kie to have 2 muffler(center &rear) with CATless.Which way is appropriated?

[merlin's S4]

Twin 2.5" is probably ok but 3" is definately better in many ways!

[merlin's S4]

I have a 3" with two Magnaflow silencers (mufflers) and a 100cel race cat. The cat is necessary here to pass the emissions test but you may not need it over there. Two boxes are essential in my opinion. It will be far too loud otherwise!

[popdemonic]

Thanks a bunch for your Input Tris.Ok I'd go for that route.
Anyway,with 2 mufflers is the way too loud?Maybe it needs one additional small muffler??

[merlin's S4]

Two boxes is just right. A single box system will be extremely loud!

[gedu]

twin 2,5" flows in fact more than single 3", you can calculate flow area yourself, PI*r^2

On UrS4/6 you can get away with only single box, and still hear your thoughts inside, at least if you have sedan. BTDT and got the t-shirt Down pipe should be 3", will wake up the turbo better, after that, it's all up to you, 3" minimum

[Acidburn]

On UrS4/6 you can get away with only single box, and still hear your thoughts inside, at least if you have sedan. BTDT and got the t-shirt Down pipe should be 3", will wake up the turbo better, after that, it's all up to you, 3" minimum

Thats good to know :mischeif:

[gedu]

The most important part with single box exhaust on Urs4/6 is that you need tip coming out of bumper, and preferably some straight section (15-20cm) after the box (if box fitted to rear silencer space). Not that loud inside, but oh yes, bystanders will hear you

[Acidburn]

The most important part with single box exhaust on Urs4/6 is that you need tip coming out of bumper, and preferably some straight section (15-20cm) after the box (if box fitted to rear silencer space). Not that loud inside, but oh yes, bystanders will hear you

any chance you have any pictures of a system so I can see what it looks like as I will need a system very soon for mine, was thinking full 3 inch downpipe back with a removable cat.

been looking for decent videos to see what they sound like, i always found my s2 too quiet and boring.

[merlin's S4]

twin 2,5" flows in fact more than single 3", you can calculate flow area yourself, PI*r^2

It's not all about volume, with the twin 2.5" you have more wall area and hence more resistance.

[Jamo]

twin 2,5" flows in fact more than single 3", you can calculate flow area yourself, PI*r^2

On UrS4/6 you can get away with only single box, and still hear your thoughts inside, at least if you have sedan. BTDT and got the t-shirt Down pipe should be 3", will wake up the turbo better, after that, it's all up to you, 3" minimum

Exhaust is not about cross sectional area and volume it's about gas flow, the best exhaust is the shortest one of the same diameter all the way through.

A straight through 3" exhaust will gas flow better than twin 2.5

[GazzaG60]

2x2.5 may flow better but we have a single pipe from the turbo not 2. this then would need to go into 2 pipes causing a turbulent point. 3" straight through wont have that issue.

the area of the pipe, is very important as long as it flows well.

save hassle, money and time and go 3"

[popdemonic]

Well,What about the downpipe? 3" or 3 1/2"? I'm thinking to go for the 3 1/2" as the price is the same.

[Jamo]

Bigger the downpipe less backpressure on the turbo, although do be careful you can have too big a downpipe as turbo's work on pressure differential between inlet and outlet, too big a difference and the seals suffer.

For a 2871r the 3" is perfect, if you planning to upgrade in the future then get the 3.5" it will be noiser.

[Mr.Crossfire]

Seals suffer?