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Exhaust Emissions Test  Rate Topic 
 Posted: Fri Jul 10th, 2015 01:06 am
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Joined: Sat Mar 2nd, 2013
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I asked myself could I have been wrong?

I tested a BMW X5 4.4 litre, the exhaust arrangement is two down pipes from the engine V Banks, one down pipe each bank, which then meet up after the CATs at the centre silencer, each front branch pipe bolted to this centre silencer, then two pipes at the rear of this centre silencer going to two separate tail pipes at the rear.

I thought, this is treated as a single exhaust system, where the regulations advise us that if the exhaust system has at least one point in the system where all the exhaust gasses from the engine travel through the same pipe, even though the system may split at some point to separate the silencers or tail pipes, then for emissions purposes only one tail pipe needs to be checked.

This centre silencer by visual examination on the vehicle cannot possibly be known whether the silencer internally is separated from each branch, or whether the gasses at that point through the silencer actually mix and then are distributed through the two tail pipes.

During the test I tested the emissions through the nearside rear tail pipe, the co was too high at cruise speeds and hence failed the test.

The BMW had been taken to another Test Station and the NT at that station tested the emissions through the other offside rear tail pipe, the emissions through that pipe passed the test criteria.

Today the BMW came back advising of this, so I checked both tail pipes and found the co to be 3.96% on the Left Bank and 0.199% on the Right Bank, the result = 2.07%

The regulations say that A Dual exhaust system has two separate pipes from the engine manifold all the way back to the tail pipes. An exhaust system with a balance tube between separate pipes is still considered a dual exhaust.

Is the X5 centre silencer a balance pipe?

Should I consider the metered results from each tail pipe to be telling me that the centre silencer is two separate silencers built into one unit?

How would one know?

What is the correct test procedure for this system?


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