Catalytic Converter Location

[S-4Motion]

I've been looking at various downpipes, and I've noticed that they either have the cat right next to the turbo, or on the pipe that connects the downpipe to the rest of the exhaust (seen below). I know having the cat as close to the engine as possible means it does it's job sooner, but what is the advantage of having it be out of the engine bay and under the car?

 

[Rodcollier1]

I believe the advantage is the ability to replace it when it wears out. Obviously cheaper also since it’s just a weld on part instead of integrated. Making sure the cat works well enough to prevent a CEL without a tune that covers it up is the most important thing for me.

 

[Jimdog]

Putting it further down the line let's the exhaust cool a bit before it heats up again as it goes through the cat. For road cars closer to the engine is better because it heats the cat up faster for better cat efficiency. I believe there was a Honda civic that had the cat built into the exhaust manifold. For performance cars it makes sense to put it a little further away. Race cars have put cats in the tailpipe according to the Subaru launch control video I watched. This lets the exhaust gases reach reasonable temps so they don't melt the cat. That's in a car that is expected to run hard for extended periods of time. They claim that it only accounts for 3-5 horsepower.

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[S-4Motion]

Putting it further down the line let's the exhaust cool a bit before it heats up again as it goes through the cat. For road cars closer to the engine is better because it heats the cat up faster for better cat efficiency. I believe there was a Honda civic that had the cat built into the exhaust manifold. For performance cars it makes sense to put it a little further away. Race cars have put cats in the tailpipe according to the Subaru launch control video I watched. This lets the exhaust gases reach reasonable temps so they don't melt the cat. That's in a car that is expected to run hard for extended periods of time. They claim that it only accounts for 3-5 horsepower.

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Well as much as I want to pretend my Sportwagen is a race-car, it isn't. Very interesting info nonetheless. I had also heard that having the cat outside the engine bay would reduce temps in the engine bay, not sure if that has any merit.

 

[jimlloyd40]

Well as much as I want to pretend my Sportwagen is a race-car, it isn't. Very interesting info nonetheless. I had also heard that having the cat outside the engine bay would reduce temps in the engine bay, not sure if that has any merit.

That makes sense to me. Exactly my thought.

 

[jimlloyd40]

I believe the advantage is the ability to replace it when it wears out. Obviously cheaper also since it’s just a weld on part instead of integrated. Making sure the cat works well enough to prevent a CEL without a tune that covers it up is the most important thing for me.

Who would weld a new cat in without removing the DP anyway?

 

[Rodcollier1]

Who would weld a new cat in without removing the DP anyway?

Converters are often on a separate pipe, because they are known to need replacing.

WRT heat and cooling down ... ceramic headers and header/downpipe wraps are designed to keep the exhaust gases (inside pipes) as hot as possible because hot air exits faster and performs better.

 

[jimlloyd40]

Converters are often on a separate pipe, because they are known to need replacing.

WRT heat and cooling down ... ceramic headers and header/downpipe wraps are designed to keep the exhaust gases (inside pipes) as hot as possible because hot air exits faster and performs better.

Right but a few posts ago you said weld in.