Maverick1975

I assume the primary cat set up on the C63 black series is same as stock but if I replace the primaries with hi flow cats do I need to modify the 02 sensors or do they plug into pipe ahead of primary cats. I basically want to cut and paste in hi flow cats but want to know if I need to relocate O2 sensors before I head down to exhaust shop and get car on hoist.

Maverick1975

No matter, question answered already. 02 sensor in front and behind primary cat. Been advised I will need to either a) tune engine to account fo hi flowing cat or b) fool the computer with an insert into the rear 02 sensor that will make computer think exhaust gases had retained their previous velocity/temp. Changed my mind and now putting in a different resonator to see if I can get the effect I am looking for - which. Is even more crackling and popping and a fraction more volume. Changing cats wasn't going to do that anyway apparently so all good.

DuaneC63

It depends on the tune and the cats. If the surface area of the cats is the same (ie if a large 100 cell cat has the same surface area of a small 400 cell cat) your O2 sensor should not know the difference. A tune needs to take into account the flow volume of the cats in addition to its cell count. Most tuners will ask you what other mods you have done to your car and adjust the tune accordingly.

Maverick1975

Well the stock cats are very large in diameter and look to be 500/600 cell having seen inside them today. The cats I was contemplating were probably half the diameter and 200 cell.

I had to scratch my itch so I removed the rear resonator fabricated by Sebring and put in ones fabbed by Mille Miglia. The 1 foot long Sebring resonator has two distinct tubes inside with a small hole in each pipe towards the back of them connecting the two chambers, basically a cross pipe. There is also a small area of perforation inside each chamber but 60% of the length of each chamber is smooth. The new ones I had installed are not connected and have more perforations. The net effect of this is a slight increase in volume, slightly deeper note, no drone and a bit more of the warbling/throatiness on overrun & downshifting that other Black Series owners will be familiar with.

All in all it's toughened the sound up a notch further but had less of an overall effect than removing the secondary cats did. That particular step had a great impact on sound, yielding a deeper note and more crackle & pop.

I have been thinking about it all afternoon on bondi beach and I think electric cutouts might be the next step...

MaroonC63

Who said cats doesn't make more popping sounds? My 09 with straight pipes instead of the resonators sounded like stock but on roids, not as loud as LTH but DEFINITELY way more pops and crackles. I just removed my primaries, and the exhaust crackles and pops when i let off the gas after 1.5 rpm. Even if im at 10 MPH itll crackle and pop tons when it slows down to 0. Sounds like gun shots

Maverick1975

So you have no resonators AND no cats?? Did you retune because apparently the ecu will be expecting to see significantly slower exhaust gases pass the second of the 2 O2 sensors. Thought you might have gotten a CEL.

Was it dramatically louder with no resonators, surely there must have been more drone?? Maybe I just chop out res altogether and just run primary cats??
Or go cutouts to control volume better, my neighbours freaking hate me as it is...

MaroonC63

Yes sir! Sounds like a monster truck as my friends would put it haha. I actually didnt get a cel when i took my primaries out till after 500ish miles. But jerry at eurocharged fixed that for me! When i chopped my resonators AND secondaries, there was absolutely no drone. Didn't even sound any different inside the cabin. When i only had resonators, the downshifts were INSANE but sounded exactly the same inside the cabin. X pipes Y pipes Straight pipes, done them all. Only time the sound in cabin changed was when i removed my primaries. But the sound it makes now makes excited me more than my cold starts,although very obnoxious haha.

Go with the resonators first, then the secondaries if thats not enough for ya, thats if you dont mind chopping off your exhaust.

Maverick1975

Thanks I have chopped out secondaries the day after I bought it! Maybe I try straight pipes instead of aftermarket resonator.

Ezec63

So I dont get what your setup exactly is? You just had your secondary cats removed and replaced with a resonated cross pipe than switched that to a resonated straight pipe?

I'm curious because my c63 is currently in the shop for a quaife LSD and secondary cat delete we are going to be chopping off 2nd cats and replacing with 2 12inch straight pipe resonated bullets. Hopefully it sounds good

Maverick1975

Incorrect. I had the secondary cats removed a while ago and replaced with straight pipe - this is an awesome simple mod. In addition I subsequently had the stock resonator which has what appears to be a cross pipe arrangement in it removed and replaced with an aftermarket one. So I have primary cats, aftermarket resonator and then stock mufflers.