Questions about mid pipe upgrade

[tonywham]

Sorry about asking noob questions here. I am a newbie who is researching about the exhaust mods, and am thinking about the mid pipe upgrade (say like AA mid pipe). However, what confusing me is I think the mid pipe will delete the secondary cats on our cars, how come people having the mid pipe never mentioned anything about fumes or emission issues. Is that because the secondary cats are not as important as the primary cats, or something else. Also, I think installing a mid pipe will only change the sound when the exhaust flaps are open, like setting the throttle in sports or sports plus to hear more pops and burbles. But when the flaps are closed, like normal driving (in comfort mode), what are the benefits of upgrading the mid section, except for slightly hp gain?

[M4 GTS]

Downpipes have main cats. Removing mid pipes will not give you any gain in HP.

[mike@x-ph.com]

OP,
Most states use OBD testing, car will still pass this test as long as car has stock downpipes

Originally Posted by M4 GTS

Downpipes have main cats. Removing mid pipes will not give you any gain in HP.

Its actually been proven that AA midpipe add HP .. Andrew posted couple dynos from his car

[tom @ eas]

Originally Posted by tonywham

Sorry about asking noob questions here. I am a newbie who is researching about the exhaust mods, and am thinking about the mid pipe upgrade (say like AA mid pipe). However, what confusing me is I think the mid pipe will delete the secondary cats on our cars, how come people having the mid pipe never mentioned anything about fumes or emission issues. Is that because the secondary cats are not as important as the primary cats, or something else. Also, I think installing a mid pipe will only change the sound when the exhaust flaps are open, like setting the throttle in sports or sports plus to hear more pops and burbles. But when the flaps are closed, like normal driving (in comfort mode), what are the benefits of upgrading the mid section, except for slightly hp gain?

There are no gains in midpipes, only sound. BMW has done an excellent job in exhaust design.

[Rbezy]

I have catless downpipes and AA midpipes. Yes you have the smell of fumes I wouldnt pass emissions either. With the stock muffler I was able to keep my flaps and control them with a JB4. When I close the flaps its like driving with a stock exhaust.

[horsepower_and_hounds]

Originally Posted by mike@x-ph.com

OP,
Most states use OBD testing, car will still pass this test as long as car has stock downpipes



Its actually been proven that AA midpipe add HP .. Andrew posted couple dynos from his car

Except...... CA, visual usually catches it...if not most fail sniffer

[Fugazii]

One important thing about AA mid pipe is that it eliminates rasp.

[tonywham]

wow, thanks for quick responses. how do you guys think about dinan x-pipe, which doesn't delete the secondary cats. I just know it will not allow the flow to move as free as other mid pipes which delete the secondary cats.

[mike@x-ph.com]

Originally Posted by ehagerty

Except...... CA, visual usually catches it...if not most fail sniffer

Do midpipes fail sniffer test?
Can anyone confirm?

[tom @ eas]

Originally Posted by tonywham

wow, thanks for quick responses. how do you guys think about dinan x-pipe, which doesn't delete the secondary cats. I just know it will not allow the flow to move as free as other mid pipes which delete the secondary cats.

Secondary cats are very little restriction, if any.