Cat back system for a 4.2 V8

As an upgrade cat back system, what is best or does it not matter?

A) From the two cats two pipes into a double centre box and then two pipes into the double back box?

B) two pipes into two single center boxes and then two pipes onto a double back box?

I'm confused

my car is at http://www.powellsperformance.co.uk/for an exhaust at the moment. I was quoted £350 all in but got a call saying they didn't reliese when quoting the job the A8 was a twin pipe system so have now upped it to £500 all in but don't have any twin back boxes in stock.

The boxes Powells use come from http://www.eurosportexhausts.co.uk/Our%20products.html

[Conan_the_Librarian]

Didn't know they were quoting for an A8? More likely didn't know what an A8 is! Keeping the twin pipes seperate maintains the V8 burble. The more time the pulse spend in a single tube the smoother the purrrr will be and the less like a V8 it will sound. A twin back box is a must imo. £500 is not unreasonable for a catback stainless system given the price of stainless atm.

[jayzee]

This H pipe fitted as standard... was this incorporated into the design of the S8 to help them increase horsepower?

Conan, I'm guessing that having one kind of works against your description of the V8 sound as it blends the banks together - more so with an x pipe too?

Is this why the S8 4.2 sounds so different to the S4/RS4 4.2? They are really gruff by comparison.

[Conan_the_Librarian]

Originally Posted by jayzee

This H pipe fitted as standard... was this incorporated into the design of the S8 to help them increase horsepower?

Conan, I'm guessing that having one kind of works against your description of the V8 sound as it blends the banks together - more so with an x pipe too?

Is this why the S8 4.2 sounds so different to the S4/RS4 4.2? They are really gruff by comparison.

The 'H' pipe smooths out the sound a bit as does the 'x' pipe. A 'X' pipe will also allow better scavenging in a fixed rev range. As a V8 dosn't fir all 8 cylinders in a symmetrical pattern it gives that V8 burble unlike 2 x 4 cylinders would. connecting the exhaust for a short length helps smooth the sound. This articles explains a lot.

[jayzee]

Cheers for the link Conan

So am I right in thinking the S4/RS4 4.2 has no link between the pipes then?

I heard one on full chat funnily enough today, and that 4.2 sounded nothing like my S8!

Just spoke to the garage they say the car will be finished tomorrow after having it for 7 days!!!

I asked the bloke on the phone to describe what they have done and he went and had a look and said from the cat back its twin pipe system all the way using FIVE twin entry & exit boxes in total.

FIVE???? seems a lot???????????

what are the implications of 5 boxes in total rather than say 3?

Thanks