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      03-16-2015, 11:23 AM   #1
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Non M secondary cats

My 04 exhaust in regards to the secondary cats looks nothing like what RealOem shows.
Can anyone confirm they have the same set up on their 3 litre 03-05.

If the longer rectangular canister is indeed the secondary cats, I intend to remove it and put a crossover in its place. I will be leaving the resonator and stock can as-is for now.
I will also be welding in 2 - O2 sensor bungs so that the post cat sensors have somewhere to live seeing as they have been in limbo since I put on the header.
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      03-16-2015, 08:30 PM   #2
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I'm fairly certain the rectangular section is a resonator. When I swapped in aftermarket catless headers, you could really smell the unburned fuel. The car smelled like it was catless. Since then I've added tiny Magnaflow cats (too small to fool the ECU), and the fumes are reduced by about 80-90%.

If you ever want to pass OBD2 readiness, the rectangular section is about the only place you can add cats large enough to pass emissions without sacrificing ground clearance.
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      03-17-2015, 08:23 AM   #3
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Quote:
Originally Posted by pokeybritches View Post
I'm fairly certain the rectangular section is a resonator. When I swapped in aftermarket catless headers, you could really smell the unburned fuel. The car smelled like it was catless. Since then I've added tiny Magnaflow cats (too small to fool the ECU), and the fumes are reduced by about 80-90%.

If you ever want to pass OBD2 readiness, the rectangular section is about the only place you can add cats large enough to pass emissions without sacrificing ground clearance.
Josh ya not sure why I wrote secondary cats, I know non M's don't have them.
As you know I put dual cats in the area where the resonator is on my custom exhaust(sold btw)
I am going to try the simulator approach on this one.
I picked up an oem exhaust at the local yard for peanuts to experiment with.
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      03-17-2015, 09:26 AM   #4
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I think secondary cats were only off the 3.0si (n52). I know for a fact my original exhaust had them. The secondary cats however don't have any holes to plug sensors into.
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      03-17-2015, 10:29 AM   #5
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I'm interested to hear how the simulator works out. I've heard the ECU measures cat light off time, so I'm curious as to how it will handle the new setup. I would recommend dual Y-pipes over a single fabricated X-pipe, because the X-pipes I've seen don't look like they will split the pulses equally between both exit pipes, so you won't get the full effect of the scavenging. You could always test it by blowing into one side of the X-pipe and see if it comes out equally between both of the exit pipes.
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      03-17-2015, 11:11 AM   #6
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The uk rhd versions have secondary cats at that place, but this is just a resonator (2x straight perforated tube with fibre).
That's where I've put my cats (which barely pass the MOT.... 0,2g/km HC)
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      03-17-2015, 11:21 AM   #7
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Quote:
Originally Posted by pokeybritches View Post
I'm interested to hear how the simulator works out. I've heard the ECU measures cat light off time, so I'm curious as to how it will handle the new setup. I would recommend dual Y-pipes over a single fabricated X-pipe, because the X-pipes I've seen don't look like they will split the pulses equally between both exit pipes, so you won't get the full effect of the scavenging. You could always test it by blowing into one side of the X-pipe and see if it comes out equally between both of the exit pipes.
Like this 2 into 1 into 2. Will there be major restriction at the 1 location?
http://static.summitracing.com/globa...x-su2-2_ml.jpg
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      03-17-2015, 03:30 PM   #8
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It depends on the size. Pi * radius^2

2 (2") to 1 (2.5") would work. That way when you reverse the process (1 to 2), you aren't reducing the cross sectional area of your plumbing.

The pulse would travel down a single 2" pipe until it hit the first Y, where it encounter pulses from the other cylinder bank. It would be pulled into a single 2.5" pipe. From there it would be split into the two 2" pipes of the 1 to 2 Y-pipe. Each time there is a change in the piping, cross sectional area increases.

I would think a single 2" pipe would be too restrictive for 330+ horsepower, like if you went 2 (2") to 1 (2").

A 2 (2") to 1 (3") wouldn't be ideal because area increases with the first Y-pipe, and then decreases when you go back to your dual 2" pipes.

The best setup IMHO is to ditch the stock system and go with a 2 (2") to 1 (3"), and keep the single 3" pipe all the way back. I like the Supersprint setup because the Y portion is less dramatic than some of the off the shelf components. On the Supersprint system, the transition is gradual.

This is just my opinion based on broad interpretation of theory. To know for certain, all of the setups would need to be dyno tested.
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      03-17-2015, 06:02 PM   #9
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Thanks Josh
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