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Decat/DPF Can someone explain?

6K views 7 replies 6 participants last post by  Wayno 
#1 ·
Hello. I have a e81 120d 177bhp model m sport. I've had it mapped already and a cat back system made. I want it louder so I'm thinking decat BUT is the cat the DPF or is the DPF next to the cat? I'm trying to find a decat what will fit does anyone know where I can find one? Cheers.
 
#2 ·
I THINK the cat is before the DPF, I'll be honest with you don't touch either. It won't make the car sound any better just loud and you'll render your car an MOT failure without the DPF, without the cat it just turns them in to stupid sounding chav buses that chuck smoke everywhere.

I understand it's your car and you can do as you wish but it'll do you more harm than good messing with your cat and dpf with the impending emmissions laws and just in general.

Leave well alone.

LT
 
#3 ·
The DPF is a filter that traps small particles of carbon (and I do mean carbon, not carbon dioxide). This is basically soot from unburnt diesel. The particles are trapped and when the exhaust gets hot enough they are then burned off to prevent it clogging up with the stuff. These particles are a health hazard, as they get into you (and everyone elses) lungs, and are so small they go all the way down. They cause cancers and even get into the blood and cause heart disease and a variety of complications, which is why they are fitted - to prevent you from killing more people than the ones you might hit.

The cat does not deal with particles at all; it deals with exhaust gasses, mainly carbon monoxide and nitrogen oxides. Carbon monoxide comes from incomplete combustion of the fuel. Its highly toxic. Nitrogen oxides come from the high temperatures inside diesel combustion, that starts to burn the nitrogen in the air. These will not only kill you (and other too), but on contact with water (and we have plenty of that in the atmosphere) create nitric acid (try inhaling that and see what happens to your lungs).

Governments set emissions limits to reduce (not eliminate) the health effects of vehicle exhausts. The DPF and cat are designed to meet these limits. If you remove them, you will probably not meet the emission tests in the MOT. For now, removing the DPF is not an MOT failure (provided it LOOKS like its fitted, so you have to only remove the internal parts) but VOSA will be tightening the test in the next few months, so that wont work for long.

If you want more noise, then what you really need to do it remove the muffler/silencer. This does nothing for emissions, its just designed to absorb the pressure peaks from the engine exhaust, and sound it just pressure, so reducing pressure reduces the noise. You can sound like a chav if you want, but then you will attract the attention of Mr Plod. And he will take a very close look at your car; if you have worn tyre, expect a fine and three points on your licence. If you smoke cannabis, expect a thorough vehicle search, and if significant quantities are in the vehicle expect a cavity search (so if you do remove the muffler, dont carry weed in the car). Basically, dont do anything that the boys in fuzz could give you grief over, or they will give you grief. Drive like Miss Daisy, and dont give them any excuse, which kinda defeats the point of enjoying driving.

Your choice :D
 
#5 ·
So regardless of the fact it's illegal and won't pass the MOT you'll just ignore everybody and get it done anyway. Check ebay but any exhaust place will do you a decat pipe nobody does specific pipes aftermarket as it's not something that is done much in the world of BMW.
 
#6 ·
TALBOTL said:
So regardless of the fact it's illegal and won't pass the MOT you'll just ignore everybody and get it done anyway. Check ebay but any exhaust place will do you a decat pipe nobody does specific pipes aftermarket as it's not something that is done much in the world of BMW.
Ha well said T.

He obviously had a corsa or fiesta 1.2 and thinks BMW deserves to be on the chavved list too.

2010 E82 125i modded by Babybmw.net
 
#8 ·
I've got a diesel, it's only got the rear silencer removed and the oval tailpipe switched for a twin one. I'd recommend that, maybe even have the second silencer removed rather than a DPF delete.

But unlike everyone who hates on the dpf delete route, I'd say I've heard a straight through exhaust one a diesel 1 series and it sounds epic. A bit strange for a BMW but If you want to do it, go for it but make sure you keep your dpf come MOT time.

"Modified" petrol cars do more damage than "modified" diesel cars. For every 20 decat petrol cars there's probably 1 dpf removed diesel. Just go to a car meet. How many V8's, V6's, focus RS's, vxr's, M3's, M4's and so on have had their cat's removed? And how many 120d's have had their dpf' removed?

Dpf removal causes,

Particulates to escape which may include sulphur and causes,
Major respiratory and health problems.

Decat'ing causes,

Exhaust gases that were supposed to be broken down to H2O, N and CO2 to remain N2 and worst of all, the quiet killer CO

Global warming

A diesel car technically runs way cleaner than a petrol car with the dpf on. Without, it's just a soot machine.

Petrol cars run cleaner with a cat on but mess up the ozone without.

They all do irreparable damage, the only difference is that with a diesel, you see it happen because of the black smoke.
 
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