[Bettertomorrow]

Originally Posted by McIntoshMotorSports

Shouldn't be too much of a difference with those downpipes since they are 400 cell just like OEM cats, they may be designed to flow a bit more but for $3K not sure if that's really justified imo.. most catted down pipes are 200 cell instead such as ARM's offerings; these types of cheaper catted downpipes will definitely cause a CEL and are not EPA certified but for my needs of strictly sound they work much better than stock by providing more volume but without the rasp and tons of smell of going full catless.

There was another thread that talked about how different material used in GESI cat flows more. Still on the fence about AA catted dp. Stock DP with MHD Stage 2 seems to hold up pretty well so far. When I see oddity in data log, I will consider it more.

One interesting observation is this.

Stock primary cat has 400 cell and stock secondary cat has 200 cell, total of 600 cell. When OTS tuners recommend DP for stage 2, there is no recommendation for removing secondary cat, meaning they may be targeting 200 cell (secondary) in the system.

Adding 200 cell DP makes total 400 cell.

Removing secondary cat via straight pipe makes total 400 cell, essentially the same as 200 cell DP with stock mid pipe, but no CEL light, emission compatible!

Of course, above simplification does not factor in materials used.