Help needed real quick!!

**Dan850T5** · Friday 27th February 2009, 13:02

Hi all,

i'm about to take my car for a cat back system. Being as it's turbo, if i remove the centre box and have a pipe to a back box instead is that gonna screw the emmissions up and make it run like a bag of ****e?

Or am i better replacing the centre and having a pipe to the back?

Help please!!

**T5 ROB** · Friday 27th February 2009, 13:07

Hi mate, I've just got a cat back system with just a back box and it runs fine, although a bit loud when cruising.

Cheers, Rob

**850twr** · Friday 27th February 2009, 13:38

just have the rear silencer fitted mate, they sound pants with 2 silencers.

**Big Pete** · Friday 27th February 2009, 16:55

Originally Posted by 850twr

just have the rear silencer fitted mate, they sound pants with 2 silencers.

100% agree!!! Only cat and 1 back box required, its louder but thats why they call them silencers, you remove one it gets louder and sounds awesome!

**flyingbrick** · Friday 27th February 2009, 16:58

Wotever you do from the cat back it wont mess up the emmisions or the running.....

**Dan850T5** · Friday 27th February 2009, 17:17

Ok cheers guys, the exhaust man today reckons if i have a pipe to rear box it would be really loud?? And he's quoted me 180 for 2 boxes. What to dooo?!

**Dan850T5** · Saturday 28th February 2009, 00:23

I think i'm gonna go straight through centre to back box. If its a custom guy it wont be ridiculously loud will it?

**850twr** · Saturday 28th February 2009, 01:17

no it wont be silly loud, the noise is progressive to your right foot anyway so can be kept down when needed.

**Dan850T5** · Saturday 28th February 2009, 07:59

cheers for the help guys. Am i right in saying it will only be a small back box too? Doesnt look like much room to get it in

**flyingbrick** · Saturday 28th February 2009, 08:31

Good morning. I have a tiny box after the cat then the exhaust splits into two pipes either side. It is loud ish but not as loud as a subaru. Am happy with it makes me smile. Good luck with yours pal.......

**Big Pete** · Saturday 28th February 2009, 09:16

Are you going for a 2.5" system, did you ask what size pipe they have as I'm sure they only have 2.25" pipe and that isn't good enough if you are having a custom system 2.5" or 3" all the way is the way forward.

**Dan850T5** · Saturday 28th February 2009, 09:37

so if its only 2.25' will it run like ass?

**p fandango** · Saturday 28th February 2009, 09:41

Originally Posted by Dan850T5

so if its only 2.25' will it run like ass?

it will run fine, its about the same size bore as standard. Just replacing the standard silencers with performance once will make a big enough advantage so should still notice the revs freeing up

i'd only bother with anything bigger if you intend to do much more mods on it (ie bigger tuebo etc), i ran a Powerflow 2.25 for many years & was more than happy with it

**Dan850T5** · Saturday 28th February 2009, 09:57

cheers for clearing that up mr p fandango, i am def not going bigger turbo, im only 20 and its not very insurance friendly to me as it stands haha.

**mexybhouy** · Saturday 28th February 2009, 13:06

the turbo reduces noise allready before it get's to the boxes compaired to a normally asperated 20v engine which i've tried with one backbox on! deafening! the turbo engine with one back box was nice and throarty and not too loud!

**Big Pete** · Saturday 28th February 2009, 13:53

Just think with a turbo the more cold air you can get into the engine and the easier you can get fumes out the better the engine and the turbo can breath as it less restrictive.

If you think about re-mapping the engine which you can get for only £150 at HLM if you haven't already, the bigger the exhaust piping the better I would imagine. Re-mapping is an easy and cheap as well as safe, generally, way to increase power from the stock car. And I just think if you are doing an exhaust and haven't already re-mapped you already in the thoughts of modifying the car so may think later you wished you had gone for a bigger exhaust, I know I have been there on other cars.

Most aftermarket exhaust for the 850's (Ferrita, BSR etc) are a 3" downpipe with race cat, and 2.5" cat back exhaust, so I just think if you are going for more of a stock piping diameter you won't be gaining as much as you could be.

Just my thought on it.

**p fandango** · Saturday 28th February 2009, 14:14

Originally Posted by Big Pete

Most aftermarket exhaust for the 850's (Ferrita, BSR etc) are a 3" downpipe with race cat, and 2.5" cat back exhaust, so I just think if you are going for more of a stock piping diameter you won't be gaining as much as you could be.

he'll still be running the standard downpipe & cat so alot of restriction will still be there.

i'm running a 19t with Ferrita 3" downpipe & race cat going to a Powerflow 2.25" single box system, plus an exhaust bypass valve 1foot away from the turbo. I can't say i've opened the valve much as the car is used mainly on public roads but there isn't much difference powerwise between open & closed. Turbo spins up a bit easier but not as much as the decat & backbox (with 2.25" pipe) did on my old 15g set-up

**Dan850T5** · Saturday 28th February 2009, 20:11

well its on and i love it! We ran it with the silencers off first and it really wasnt that loud so iv had a pipe through to a tiny backbox and quite a ahh tip haha. Cheers to everyone that helped with my questions and i will get pictures up tomorro for you all to see.

**p fandango** · Saturday 28th February 2009, 20:28

Originally Posted by Dan850T5

well its on and i love it! We ran it with the silencers off first and it really wasnt that loud so iv had a pipe through to a tiny backbox and quite a ahh tip haha. Cheers to everyone that helped with my questions and i will get pictures up tomorro for you all to see.

aslong as your happy with thats the important thing, did you notice any difference in the performance?

**Big Pete** · Saturday 28th February 2009, 20:34

Glad your happy! When I bought my car the cat had been removed and it had 2 back boxes, it was loud! But it sounded awesume for sure, like a V8, got the stock cat fitted so I could pass MOT and that has killed the loudness.