[Jet1990]

Hi all,

been thinking about doing this for a while now. I recently had a custom made backbox installed and the sound difference is really good ( nice and deep on the low-mid revs and raspy on the higher ends)

I know the car has 2 primary and 2 secondary cats and i was thinking of removing the 2 just before the backbox....now heres the part thats puzzling me. I know that after the 2 secondary cats when the pipe merges there is a nitrogen sensor between those and the backbox. If i remove the cats am i right in assuming the car will detect the difference in exhaust gas and mess the fuel/ air mix up as well as throw the emissions light on and maybe even put the car in limp mode. Every single remap place ive contacted says they can map out 02 sensors but not nitrogen sensors so im keen to hear if anyone has done it one here and what the outcome was.

thanks

[jamherber]

Assuming you have the N53 engine, the set of cats nearest the back box are the NOx cats and it's the NOx sensor that is behind them. If you remove them no engine warning light will illuminate but there will be 'shadow' codes always present for NOx emission errors. It will also mean that the engine will not run in its super efficient stratified mode so you'll lose potentially 10 to 15% mpg (compared to a std engine with the NOx system working).

[Tr1ppy]

Will there be pops and crackles from just removing the secondary cats?

I too don't really want to remove the backbox

[Jet1990]

Originally Posted by Tr1ppy

Will there be pops and crackles from just removing the secondary cats?

I too don't really want to remove the backbox

i hope so lol

[Jet1990]

Originally Posted by jamherber

Assuming you have the N53 engine, the set of cats nearest the back box are the NOx cats and it's the NOx sensor that is behind them. If you remove them no engine warning light will illuminate but there will be 'shadow' codes always present for NOx emission errors. It will also mean that the engine will not run in its super efficient stratified mode so you'll lose potentially 10 to 15% mpg (compared to a std engine with the NOx system working).

I spoke to the guys over at motorsport developments regarding the Nox sensor. They said nox sensors dont play any part in the mix of fuel to air so all I'd have to do is remap my 02 sensors out and i should be fine.

[Chappers 71]

So no concerns about the extra pollution your cars going to be putting out then?

[jamherber]

Originally Posted by Jet1990

I spoke to the guys over at motorsport developments regarding the Nox sensor. They said nox sensors dont play any part in the mix of fuel to air so all I'd have to do is remap my 02 sensors out and i should be fine.

The NOx system doesn't have a direct effect on fuelling but does allow the engine to run in stratified mode in certain situations (this is a very lean mode, hence the amazing mpg these engines can return). Removing the NOx cats will just mean it will always run in homogeneous mode which is fine, you'll just get slightly worse mpg and some shadow codes.

[ChawenHalo]

Don't you get problems with changes in back pressure with NA cars if you this? Recently been in a V8 RS4 that had been decated and it sounded shite...