After a few years with a NA V8 S4 and now with my MCS, the mantra, dyno backed, is that the exhaust gains are in the downpipe and not from the cat back. What is special about the construction of aftermarket DPs compared to OEM DPs? Is it the high flow cats?
Why does it seem like manufacturers have unlocked most of the power from the cat back and not from the turbo to the cats? It seems like a simple design for engineers to fix for easy power gains.

Thanks for your input.

 

I'm no exhaust magician, but I would say it is to keep volume and emission levels down. I mean, not too many people want to drive a Toyota Camry, Honda Accord, or even a MINI Cooper that is too loud or throaty.

Some cities have strict decibal laws, too.

 

The combination of larger pipe and better cat efficency is the reason. You are opening up the exhaust so morespent gas can leave at a faster rate. Like a garden hose with 100% water pressure with a kink it may only flow 50%. Unkink the hose and you get your full capacity flow. my 2 cts...
The only companies who would make a better DP than aftermarket would be the really expensive exotics. I mean even my Toyota w/ a 22r gained hp when I added a header. Factory parts are never overall perfect at maximizing power tahst not what they are designed for. They simply are the baseline for manufacturing and reliablility...usually

 

I agree. I say OEM parts and design are based on the most cost effective and maximum profit... as far as the performance, make it good enough... not great...

Now even on the sibling BMW, they've cut corners on so many things. US E46 M3 not having the same brake rotors as Euro version, 06+ Euro version has same header as the CSL M3 (same part number). while US still got the restrictive headers (its a maze of pipes compared to the real deal)

E36 - US got robbed by not even getting the S50 B32 rated at 240 HP... Euro got the fun version of 321 HP.. why??? they blame it on Emission

MKIV Supra - I believe around 95 manual TT did not make it to the US shore due to Emission (Correct me if i am wrong.. one of those yr) Then they brought it back following yr with manual tranny...


Overall, i think its political yet marketing thing... you cant satisfy everyone and ultimately.. its business.. automakers make these things to sell to make $. We would do the same thing if we are looking at $$$ at the end of the day. Sad but true.