[Yahoo]

Does anyone on the UK forum have any experience of the catless downpipes available for the 335i platform?

What are the drawbacks of using them? What would it mean in terms of UK emissions regs if the car only has the secondary cats in place?

Many thanks.

[YvesD]

Originally Posted by Yahoo

Does anyone on the UK forum have any experience of the catless downpipes available for the 335i platform?

What are the drawbacks of using them? What would it mean in terms of UK emissions regs if the car only has the secondary cats in place?

Many thanks.

Yahoo,

The primary cats do all of the emissions work and the secondary ones clean up any remaining smells and the like. A sort of polite extra gesture.

I would imagine its a definate MOT failure without the primarys but probably not without the second set.

From what our US friends are saying, You can also expect increased noise and smells without the primarys.

Cheers

Yves

[E92Fan]

Originally Posted by YvesD

Yahoo,

The primary cats do all of the emissions work and the secondary ones clean up any remaining smells and the like. A sort of polite extra gesture.

I would imagine its a definate MOT failure without the primarys but probably not without the second set.

From what our US friends are saying, You can also expect increased noise and smells without the primarys.

Cheers

Yves

I have had catless downpipes on my car for over a year now.

The advantages are that the decreased back pressure and larger diameter of certain brands' pipes result in a much more efficient exhaust with a resultant increase in both power and torque. Throttle response is also improved due to the decrease in turbo lag.

The downsides are that there is less catalytic conversion so emissions will be higher. The rearmost lambda probes (which detect the efficiency of the catalytic converters) will need to be relocated to behind the secondary cats underneath the car, or alternatively an O2 simulator will be needed to reduce the return voltage of the probes.

There is increased noise, but for me this improves the sound of the engine. I don't have any increase in 'smell' from the car whatsoever. And my car sailed through its MOT test a few weeks ago, so seemingly no problems with that either.

There are several downpipes available on the market - the two leaders being Riss Racing and AR Design. The RR pipes don't fit RHD cars very well, if at all, because the steering rack on our cars is slightly different to the LHD version. AR Design have made RHD-specific pipes to fit, in both high-flow catted and de-catted versions.

[Yahoo]

Are you using the AR design ones Tony? - they seem to be the highest rated by far. The newer Macht Schnell ones look good also.

Would you say that there are any significant benefits in going for thermal coated ones - I suspect these are particularly worthwhile when running a DCI.