Cats! - The Unofficial BMW M5 Messageboard (m5board.com)

BURTON · 14th November 2005, 18:17

No not the ones you feed Katkins, but the ones on the M5.

Now does replacing these make a difference?! If you replace them what do you go for? What gains are to be had?!

illjah · 14th November 2005, 18:28

Remove them! Kill the world!! Spit flames out of your exhaust, and go faster.

What more could you want!! I plan to do mine as mines a '91 so will still pass an MOT without them

Cyrus · 14th November 2005, 18:41

You could put straight through pipes in and see what happens. You'd probably need a remap afterwards though.

unesential · 14th November 2005, 18:42

I jahve read somewhere that they should not be removed totally as there is not enough back pressure for normal driving. The number of cells can be reduced giving a lowered pressure and maintaining drivability with a slight bump in high rpm power.

BURTON · 14th November 2005, 18:53

Iam thinking of some 100 cells.. I want Torque but want to try and get abit more oomph

Phlem5 · 14th November 2005, 19:18

I got two bypass / straight through pipes fitted as I need to get the cats welded. I am planning to put the cats back on ASAP as the noise with s/sprint cat back system is a bit loud, there is less engine breaking and any powergains are negligable, I did think as soon as they were fitted that 2k - 4k rpm pick up seemed better and maybe a tiny bit more 6k - 7k, could just be the placebo effect though. I don't know if a re-map is required as the O2 sensor is ahead of the cats. Jahangeer reckons his cat mods are the way to go but I think most will say just leave M be.

mblaster · 16th November 2005, 03:45

OEM cats gone.
Replaced with 2 small high flow cats.
No remapping. The engine runs fine.

redl1nerpm · 16th November 2005, 09:11

with exhaust, youll hate the sound

Jahangeer · 16th November 2005, 11:46

I just about passed my MOT, which surprised me as 66% of my Kats are out.

So I took out two out of three cells from EACH bank of cats on my 3.8 and left the 100cells in. As Phlem5 said you feel slightly more torquey higher up. Not sure about hp gains.

mblaster's is also a good way to go if you want to experiment with the kats.

I think I will get another 100cell kat placed in each bank next spring so I dont have to worry about the MOT emissions being borderline - and not passing.

BURTON · 16th November 2005, 18:09

Quote:

Originally Posted by Jahangeer

I just about passed my MOT, which surprised me as 66% of my Kats are out.

So I took out two out of three cells from EACH bank of cats on my 3.8 and left the 100cells in. As Phlem5 said you feel slightly more torquey higher up. Not sure about hp gains.

mblaster's is also a good way to go if you want to experiment with the kats.

I think I will get another 100cell kat placed in each bank next spring so I dont have to worry about the MOT emissions being borderline - and not passing.

I think I will get replacement CATS!! Now who does them? G Power? Or is a normal exhuast place good enough?