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Does anyone know the internal or external diameter of the factory standard exhaust downpipe?
I did search but either I somehow missed it it wasn't there. Thanks in advance.
 

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its not just the diameter, but the constricted flow coming off the turbo.

Take a look at the photos in the GMS exhaust thread here:

Post 1 shows the cat/downpipe from right where it comes off the turbocharger. It does a 90 degree sharp bend and is constricted right there, followed immediately by the catalyst.

There is good description there as well. I suspect the dimension is given (likely around 2" to 2-1/4" but I am not sure) somewhere in that thread.. But it's the shape as much as the diameter up there that is an issue.
 

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Does anyone know the internal or external diameter of the factory standard exhaust downpipe?
I did search but either I somehow missed it it wasn't there. Thanks in advance.
Pretty sure it's 60mm the down pipe replacement I put in from Scara is 70mm.
 

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The idea behind the stock design is to get the engine up to operating temperature quickly. That helps reduce emissions and that is important from a compliance standpoint. Ideally you would have the turbo a bit farther back and larger diameter pipes but those fly in the face of keeping emissions down.
 

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