the_big_1

Hi Guys,

In the UK, C63 are not as popular in the US and modifying less so.
Looking at getting a Euro Charger map etc but in the UK, most say there is no point removing the secondary ATS as they make no difference to power, just makes the car louder and there are no dyno runs showing the CATS before and after power gain.
Can you guys comment?

datamg

I am probably completely unqualified to answer this but....I think freeing up the airflow at any point through out the exhaust, of course while maintaining the proper back pressure, helps the engine burn more "efficiently".

The more you free up the exhaust, the louder it will get at certain Rpms, but the sound is addicting. I'd be surprised if people who took out secondaries didn't consider at least for a second taking out more (i.e. Headers/resonator/mufflers)

chrisridebike8

Most people will tell you it frees up a few horses. I can't remember exactly how much but if I recall it should be around 15 hp. Most people do it for the sound. The real power comes from long tube headers, and those will be LOUD.

H20 MRV

I have had my secondary's gutted, it makes the car sound much better, Power? I don't know but I suspect a little more, Whatever you do don't chop out the secondary cats and replace them with straight pipes as you will fail your next mot.

the_big_1

How much louder are they compaired to with the CATS.
I guess if its no power increase, a normal Eucocharger map is fine and doesnt need re-doing if I take them off later.
I am either going to get some where I can swap them back at MOT time or have the originals gutted out.

Dazzagt

Had my secondary cats removed back end of last year, had the Miltek replacement pipe, all work was done by AMD tuning down nr lakeside Thurrock, part and fitting inc VAT for under 500.

No downside, wasn't looking to add more power, but it pops and crackles more lower down and on the overrun, absolutely no increase in cabin noise inside, no drone, about 3500/4000 Revs far more aggressive sounding

Just had the MOT done and all fine also, so no messing around with swapping back and forth and still have the original pipes if I need to replace and sell the Miltek

Dazzagt

http://m.millteksport.com/exhaust.pr...tepreference=2

Secondary cat bypass

Video, although even though I spent ages looking and listening there is nothing like hearing it in real life to be properly sure.