[nictobin]

I have a 2009 BMW 335D. I was wondering if I were to gut my stock downpipe but keep all the emissions plugged it, would that cause any issues? And would it make it any louder?

[whyzee125]

Originally Posted by nictobin

I have a 2009 BMW 335D. I was wondering if I were to gut my stock downpipe but keep all the emissions plugged it, would that cause any issues? And would it make it any louder?

It would function similarly to a downpipe. It will work fine to decrease back pressure and increase flow a bit. As long as you get all of the material out, it won't cause any issues. In theory you'd have a bit better performance out of a true downpipe as you wouldn't have a bottleneck by increasing then decreasing in diameter but in practice it should work about the same.

It will throw codes without a tune and will definitely make it louder.

[Tambohamilton]

It'll also stink...

[lnxguy]

You'll need a retune if you do that..

[E85 Sport]

Originally Posted by Tambohamilton

It'll also stink...

And smoke…

[maryjane]

I have a 1320 branded DP if you need 1.

[T-Dubbs]

downpipes are NOT expensive.
whats the issue? Are you cheap or poor?

[nictobin]

Originally Posted by T-Dubbs

downpipes are NOT expensive.
whats the issue? Are you cheap or poor?

Poor. And you’re an ass

[lnxguy]

This isn't the vehicle to own if you need to nickel and dime. Just sayin'. Buy a N52.

[T-Dubbs]

Originally Posted by nictobin

Poor. And you’re an ass

no offense, but ive dumped 5-7k into mine since buying it for "forgotten" maintenance and the deletes to make it reliable and not leak oil.
Its really not a budget friendly SUV.

Originally Posted by lnxguy

This isn't the vehicle to own if you need to nickel and dime. Just sayin'. Buy a N52.

100%

[Tomnavigator]

Nic
The pollutants in your exhaust are primarily organic oxides (unburnt and partially burnt fuel), soot, and Nitrous Oxides (NOx). The emissions are controlled as follows:
1) The first thing in our exhaust used to control our emissions is the Exhaust Gas Recirculation (EGR). This consists of a recirculation valve and cooler that takes some of the raw exhaust and recirculates the exhaust back to the intake manifold inlet. This is done to lower the exhaust gas temperatures which lowers the quantity of nitrous oxides formed in the exhaust. The down side to recycling exhaust gas is that the exhaust gas contains soot which is what causes the carbon build up problems in our cars when it combines in the intake with oil vapors from our crank case ventilation system. Owners remove the EGR to eliminate carbon build up. However, the EGR is needed for the diesel particulate filter (DPF) regeneration.
2) Right after the turbocharger is a diesel catalytic converter. the catalytic converter is an oxidation catalytic converter that uses an oxidation reaction. An oxidation reaction is what takes place when you burn something and adds oxygen to the compounds in the exhaust. The oxidation of the organics in the exhaust removes most of the bad smell in the exhaust. You should leave this in place because it will not cause any problems and removes the obnoxious smell from the exhaust. The typical life of the catalytic converter is 200,000 to 300,000 miles. When it fails your exhaust will just stink more.
3) Right after the diesel catalytic converter (1/4 inch gap after the catalytic converter) is the Diesel Particulate Filter (DPF). The purpose of the diesel particulate filter is to remove the soot from the exhaust. The DPF is reliable and usually lasts up to 200,000 miles. When the DPF gets full of soot, the DPF is regenerated by injecting raw diesel fuel in the exhaust which ignites and burns off the soot to reduce the back pressure in the exhaust. The only thing left are the inorganic materials that can not be burned. This is why your car requires special low inorganic solids oil. Over time the inorganics build up and eventually plug up the DPF causing it to fail. When the DPF fails, your exhaust will plug up and the car will not run.
4) The fourth thing in the exhaust is Selective Catalytic Reduction (SCR) to remove the Nitrous Oxides from the exhaust. The SCR is a special catalytic converter that works through a reduction reaction. A reduction reaction is the opposite of an Oxidation reaction. A reduction reaction removes oxygen from a compound. Nitrous oxides are formed when the nitrogen in the air is burned in the cylinder under high temperature and pressure. The SCR reduction catalyst requires urea to be added to the exhaust gasses for the reduction reaction to take place in the SCR. The Urea (commonly known as diesel exhaust fluid) is added after the DPF and prior to the SCR. The urea injection system is what causes almost all the problems in our cars.
The programming of your engine control equipment will cause your car to not run unless your engine control computer is reprogrammed with an emissions delete program. This is commonly referred to as tuning your car. Most but not all people add performance enhancements to their emissions delete tunes.

WHAT HAPPENS BY REMOVING YOUR POLLUTION CONTROL EQUIPMENT
Removing EGR causes issues with the DPF and increases Nitrous Oxides. Removing the EGR will cause trouble codes.
Removing DPF will cause the SCR to plug up with soot. Then your car won't run. Removing the DPF will cause trouble codes.
Removing the SCR can be done stand alone since it is the last emission control device. Removing the SCR will cause your car to not run and can only be done if your car engine control computer is reprogrammed with an emissions delete program.
You can remove your SCR and DPF both without significantly changing your exhaust sound. Just leave in your diesel catalytic converter (just prior to the DPF). There is no real advantage to removing the diesel Catalytic Converter and it keeps you exhaust from becoming obnoxiously smelly. The DPF and SCR must be removed or they will plug up. The diesel catalytic converter is the only thing you can leave in place without plugging up. It was designed to have the soot go through it.

[Tomnavigator]

I have a few more comments related to BMW emission control equipment.
First is that the people that do emissions deletes will gain around 4 MPG due to the fuel wasted in the DPF for regenerations. There may be 1 to 2 MPG gain from the elimination of the EGR.
One emission control device that I did not mention previously was swirl flaps. The BMW diesels have two intake valves with two inlet ports. One port is designed to make the inlet air swirl around like a tornado (a vortex effect). This is to make the air fuel mixture mix more thoroughly. The other inlet port lets the air enter without the swirling effect. The swirl flaps are in effect flapper valves that close the air off to the port that does not create the swirling. The swirl flaps close off the direct port when the engine is at low RPM (somewhere below 2000 RPM). The improvement in the fuel mixing due to the swirl vortex causes better burning of the fuel. This results in a reduction in emissions and a slight increase in power and torque.
The BMWs in Europe have swirl flaps that are known to have issues coming apart, getting sucked into the engine, and destroying the engine. The US BMWs have a different swirl flap design that dependable and creates no issues. Many people in the United States eliminate their swirl flaps when they get emissions delete out of fear that the swirl flaps may fail and because it can be done cheaply. Eliminating the swirl flaps will result in a slight reduction in power and fuel mileage. But the reduction will be small enough that it can not be measured unless it is done without other changes at the same time. In my opinion you would be better off leaving the swirl flaps in place if you are doing emissions deletes. I will probably be crusified for that last statement but it is my opinion.

[Tomnavigator]

Nictobin,
I reread your original post and am writing this to try to help you out with your car. If you want to keep your car and don't have a problem violating the law by deleting your emissions equipment, the cheapest way to do that would be to

1) Delete your EGR to eliminate the need for carbon cleaning. EGR delete will cost under $100. Carbon Cleaning varies by location but $1,000 is typical.
2) Delete your SCR. This will entail cutting open the SCR and removing the catalytic material and rewelding the case back up. Cost is variable from $100 to $200 depending on your welder and if you do the work other than the welding.
3) Delete your DPF by removing it, cutting it open, removing the DPF filter material leaving the diesel catalyst in place, and rewelding the case up. Cost $100 to $200 if you do the work other than the welding.
4) An emissions delete tune for $500 to $600 if you do the work.

Note: This is a bare bones emissions delete route with you doing all the work except the welding. If you pay a shop to do all this then expect to pay over $2000.
After you do this you will have a car that gets 4 to 6 MPG better fuel mileage and will be fairly dependable.
If you are not a do it yourself person that can do this work yourself, the best advice I can give you is to sell the BMW diesel and buy a late model 4 cylinder Toyota Camry. It will get about the same fuel mileage after you factor in the lower price of gasoline vs diesel and will be much more dependable.

[E85 Sport]

Really informative posts as always Tomnavigator.

I wish I could do a delete to realize those efficiency gains but the smoke and smell are deal-breakers. Yuck!

[Tomnavigator]

E85 Sport
Thank You. I really appreciate your positive statements. I think the whole purpose of these forums is to help others and to get help when needed.