Exhaust bore sizes

[xyber]

Ive been looking into which exhaust to go for and have noticed all the big name brands like APR and Milltek use a 2.25 system, but allot of the smaller custom brands use 2.5

Im inclinde to go for 2.25, probably Milltek, as these companies have a huge development budget so they must see some benifit from the 2.25 set up

Obviously the 2.5 system will be louder, but would it make more bhp at the sacrifice of torque or anything like that?

Can anyone shed any light on the different paths these companies take?

Thanks

[BlingBling]

The only thing you pay for with name brands is the name. I have a full custom system with 2.5" bore and I am very happy. Performance and noise is spot on. In fact I am nearly a £1K happier than if I'd gone for a named brand. Save your money and put it towards the remap you will need after the zorsts have been added.

[xyber]

what have you got then? Im considering 2.5 for the whole lot, main cats (200cpi) and non res system, not sure on if i should have an X or H pipe? A I understand X gives more BHP, H gives a deeper tone more than anything

[BlingBling]

I have straight down pipes, 100 cell main cats, h-pipe, non res catback. All 2,5". Plus a JD Engineering map.

[xyber]

Cool cheers mate, Ill probably going for the H-pipe as I prefer the noise. Whats cats do you use? I spoke to magnaflow and they recommended the spun cylinder 200's and to stay clear of the 100's on this application

also what induction set up do you use, I like the carbino carbon fibre one, but thats just bling really so thinking about an MRC panel filter one if they do it or similar, just so the bay looks tidy and OE

[BlingBling]

I have 100 cell cats. No sure how it is spun. What reason did magnaflow give for staying clear of 100 cells?

I have the OEM airbox with a K&N filter. Not convinced that induction kits actually yield any benefits due to the hot engine bay temps.

[xyber]

Havnt got round to asking about the cats yet, but have heard that some people think that the 100's are to close to the emissions limit for comfort and worries about reliability

Im definatly gonna keep the air filter enclosed, wether its with the OE box or one of the other enclosed types around

[xyber]

Having do a lot of research this week, I think im gonna go for a milltek non-res and maybe get the DPs custom made and stay with a 2.25 bore size.

There seems to be a hell of alot of science that goes into designing a system so I think doing it this way I will get the best of both worlds with a cheaper alternative to the milltek DPs, with a properly tuned exhaust that give the power and torque at the best 'usable' rev range for what I want