Join Date: Jan 2013
Location: Peterborough (UK)
If you leave the CAT on, you're not going to get the full benefit of the M4 as a slip on.
The note of the exhaust will be a bit deeper, as the M4 is simply a straight through, Emissions will remain pretty much the same, as the CAT will be doing its job; you will not feel/get much, if any performance gains, since the bulk of the exhaust weight you would be saving with a complete system remains with the CAT and you mat get a bit of popping on the overrun, but if it's loudness you want, you will not get the FULL DB volume with the CAT!!
Personality helps, but ATTITUDE is everything!
(ABS Tourer) Made in JAPAN, Perfected in the UK
Last edited by mdr1970; 10-05-2015 at 11:12 AM.