Hello All,
Well I have a de-cat and no centre silencer on a milltek system.
I have experienced no problems and have been running it for nearly two months and covered nearly a thousand miles, what I have is a 3 inch downpipe straight onto the 2.5 inch system.
Performance wise I have not had a chance to get the car on the rolling road and have also not had it on before this pipe was done with a correct reading so cant tell the exact improvements in BHP terms, what I can say is spool up is improved as is top end and as stated below you get some more noise.
Noise wise it is not loud at idle or pottling about but once you hit 3k on WOT it gets nice an deep, you can also hear the turbo working and I dont mean wistling its kind of mechanical and I like it, it gargles a little bit but as yet no back firing on my APR chip but a small back fire on standard map on a trailing throttle which was odd.
Cost wise the downpipe and conneting to the standard cat back system cost ?129 inc VAT from milltek, the centre silencer straight through pipe was ?55 I think again from milltek.
HTH
Henry