Advice for catalyst vs decat

[Eagle]

I have been on a full decat 2.5inch exhaust for some time now.i wasnt very happy with the sound...i also have a center resonator on an attempt to keep it as silent as possible. After having aluminium boost pipes i rhink the sound was a bit more noticeable ..the sound is noticeable from around 2000rpm and also its not even a nice racing car sound..it sounds
More like a loud vaccum cleaner.
I am thinking to have a racing catalyst on my car to reduce the noise/sound.
Is it a good idea?in terms of performance will i loose any noticeable power? Also the smell of fuel will it stop after having a racing cat on my car?

[kistigun]

In terms of performance: you will loose power, but if it's noticeable? I think if you switch to a high flow race cat you wont notice any difference. With a cat the fuel smell will be gone andprobably the sound will be reduced

But you could also switch the backbox for a different sound

[Chris_Blue]

My understanding of the 2 types of catalytic converter- Sports and Race

Race Cats are only allowed on a track and are less than 200 cell per sq inch
Sports Cat are above 200 cell but well below the 600 or so OEM

Sports Cat (Which i had) increased BHP on a THP 155 by about 9 BHP and the bigger bore exhaust raised about 3 BHP.

Sports Cat will deffo be quieter than Race Cat or De-cat, as there is still a restricition

All from memory, so might not be precise

[Czar]

As you are already tired of the exhaust acoustics without a catalytic converter, forget about any catalytic converter with a cell count of less the 200 cpi (cells per inch) as you will not notice a reduction in the exhaust acoustics, you need to stop trying to build a fully fledged road car into a track orientated car, exhaust acoustics are what make driving a vehicle, a pleasure or total misery, as you have found out, to your cost, and your not alone.

My advice is to install a high flow 200 cpi catalytic converter, this will reduce your exhaust acoustics to a tolerable level, whilst removing the fuel smell, whilst still retaining a very good exhaust gas velocity.

Exhaust gas velocity is crucial, why ?

When we remove a catalytic converter and replace that with exhaust tubing, during regular street driving we do not have enough heat to facilitate efficient exhaust gas evacuation, (velocity) hence why most people feel a slight hesitation at low to mid RPM and road speed during acceleration, yet only see and feel any noticeable gain further up the RPM band, how many of you simply look at your dyno graph, and are focused only on the peak BHP figure, you will find that peak high up the RPM band, how many of you drive around on the streets, in a low enough gear to have that peak power in play ?

What you should be focusing on is getting that peak power lower down in the RPM band, to be more useful, whilst driving on the streets, which is where you need that heat, to maintain excellent exhaust gas velocity, the hotter the better, again, stop trying to build a track car out of a street car, they are two completely different animals, with power delivery in totally different RPM bands.

Here is the internal images of the 200 cpi high flow catalytic converters I use, and install at different locations within the exhaust system, for the varying different exhaust gas velocity and RPM band of the particular engine.

[JEZDS3]

High Flow Cats are the way forward then Czar,thanks for the info on that.

[Chris_Blue]

Jamie at SPT fits DS3 designated Sports Cats, he fitted mine. Think he reduced the price after mine........

Altho mine was first one. HTC from what i recall

Fantastic modification as the car feels so much "freer" and performance is noticeably better

[Jamie@SPTuning]

Totally agree with czar post, swapping out the Milltek high flow cat with decat there is now a noticeable lack of low-mid rpm punch. But come 4000rpm [emoji573]

[Eagle]

Jamie in terms of sound is it much louder with out a catalyst?

[Jamie@SPTuning]

Yes, quite a lot louder