Need Help: Mid Pipe vs Down Pipe for N55

[CL 19]

Hi guys. I got really confuse with the terms down pipe and mid pipe. I know its position is different, but which one do you recommend for better performance and sound? How does it affects the car? I plan to do just axle back but you guys make me think over and over whether to do mods with my DP and MP as well.

Just for your information, I got my car from out of state and here in California I have to smog it every two years, so I just want to make sure that those two are problems free with smog test. If it causing any problem, please let me know.

Appreciate any comments and opinions guys. Please also mention what brand and why do you recommend it. Videos and sound files might help as well. Many people say Berk mid is the best but I'm open to other brand or manufacturer since I'm new for DP and MP.

Thank you guys. Really need your help!

[dbchun]

no doubt majority of restriction is in the downpipes, they contain the first set of catalytic converters. switching DPs will give you the largest increase in power

switching midpipes is primarily for sound improvements, power increase is negligible. however i wouldn't underestimate the increase in driving pleasure from better sound though.

switching out downpipes will make your car NOT california smog legal, i'm not sure about midpipes, perhaps someone else can chime in

[froop]

As far as I know, downpipes will net you more of a gain than the midpipes.

On your model, being an N55, you only have catalytic converters on the downpipes. A lot of the N54 guys buy N55 midpipes to remove our cats as we have cats on both the DPs and MPs.

Remove the cats on the downpipes or getting them swapped for high flow race cats and increasing the diameter or the pipes will improve the flow of exhaust and will also increase the sound of the turbo however if you need to smog your car every 2 years I think you're SOL unfortunately. You will not pass emissions tests with your cats removed or modified.

In regards to the mids, I think that seeing as you don't have cats on the mids anyway you won't see a significant gain in performance by changing them to aftermarket pipes. With removal or changing to the resonators with aftermarket midpipes you will change the sound of the exhaust but it shouldn't affect emissions.

Hope that helps. Good luck!

[dbchun]

Originally Posted by froop

On your model, being an N55, you only have catalytic converters on the downpipes. A lot of the N54 guys buy N55 midpipes to remove our cats as we have cats on both the DPs and MPs.

good point! totally overlooked that you had a N55 135i. N55 midpipes don't have cats

[CL 19]

Actually I'm considering DP or MP because some people said doing only axle back will not give significant changes in the sound itself and that's why I'm asking here. So, in other words by changing my DP, I will fail the smog test? How about Mid Pipe? I just want to make sure that I'm not wasting my money for an axle back if in fact by changing my mid or down and using stock axle back will create better sound.

[froop]

Originally Posted by CL 19

Actually I'm considering DP or MP because some people said doing only axle back will not give significant changes in the sound itself and that's why I'm asking here. So, in other words by changing my DP, I will fail the smog test? How about Mid Pipe? I just want to make sure that I'm not wasting my money for an axle back if in fact by changing my mid or down and using stock axle back will create better sound.

Yes, you will fail your smog test if you change your DPs to either catless downpipes or high flow race catted downpipes.

You will be able to change your midpipe to whatever you want as in your model of car, they make no difference at all to the emissions.

In regards to the sound, you will get the most change to the sound by changing the axleback due to the muffler. The second most change comes from the midpipes due to the resonators. The least will come from the downpipes but in your case there's not much you can do to change those unless you want to go through the hassle of swapping your stocks back in every 2 years.

[CL 19]

Originally Posted by froop

Yes, you will fail your smog test if you change your DPs to either catless downpipes or high flow race catted downpipes.

You will be able to change your midpipe to whatever you want as in your model of car, they make no difference at all to the emissions.

In regards to the sound, you will get the most change to the sound by changing the axleback due to the muffler. The second most change comes from the midpipes due to the resonators. The least will come from the downpipes but in your case there's not much you can do to change those unless you want to go through the hassle of swapping your stocks back in every 2 years.

I know right, that's why I don't want to do the mod if I have to change it to stock in the next 2 years. It's not the matter of money but more to wasting time and useless. So with what you said, by changing mid pipe I would probably still pass the smog check? Do you have any recommendation for mid pipe? I'm thinking to pair it with Meisterschaft Sus-GT though.

[froop]

Unfortunately I don't have any direct experience with exhaust modifications as I haven't done any on my car just yet. All that I know I've gotten from research on this forum and others.

Best bet would be to check out youtube for videos of different midpipes but I'm hesitant to say how much difference it would make on your N55. Most people who change their midpipes are those with the N54 engine.

I would recommend just changing the axleback first and see whether you like it or not. That'll definitely make the most difference. If you're still looking for more then you could look at trying to change the midpipes.

[Gdubz]

Originally Posted by froop

Unfortunately I don't have any direct experience with exhaust modifications as I haven't done any on my car just yet. All that I know I've gotten from research on this forum and others.

Best bet would be to check out youtube for videos of different midpipes but I'm hesitant to say how much difference it would make on your N55. Most people who change their midpipes are those with the N54 engine.

I would recommend just changing the axleback first and see whether you like it or not. That'll definitely make the most difference. If you're still looking for more then you could look at trying to change the midpipes.

I've swapped my midpipe + axleback but I did it for the sound more than any performance gains. Before this n55 135i, I had an '08 n54 135i and with that one, I never modified the midpipe or axleback, I just went with catless downpipes.

I can tell you that the downpipes make the biggest performance difference, you will actually feel the difference the first time you start the car and blip the throttle, just how much better it breathes without those catalytic converters on there. Then again, I wouldn't want to have to do that swap-work every 2 years...

[CL 19]

Originally Posted by Gdubz

I've swapped my midpipe + axleback but I did it for the sound more than any performance gains. Before this n55 135i, I had an '08 n54 135i and with that one, I never modified the midpipe or axleback, I just went with catless downpipes.

I can tell you that the downpipes make the biggest performance difference, you will actually feel the difference the first time you start the car and blip the throttle, just how much better it breathes without those catalytic converters on there. Then again, I wouldn't want to have to do that swap-work every 2 years...

Totally agree with you with unecessary swap-work. What do you recommend for N55 mids? Will I pass the smog check by changing the mids? I plan to do Meisterschaft on the back but still don't know for the mids

[Gdubz]

Originally Posted by CL 19

Totally agree with you with unecessary swap-work. What do you recommend for N55 mids? Will I pass the smog check by changing the mids? I plan to do Meisterschaft on the back but still don't know for the mids

I went with CP-E because their shop is local. I bought their QuickPower™ midpipe and their axleback. The whole setup wasn't cheap, but I loooooove the sound.

BMW 135i QuickPower™
http://www.cp-e.com/products/bmw-1m/...power%E2%84%A2

[hyper1]

Originally Posted by Gdubz

I went with CP-E because their shop is local. I bought their QuickPower™ midpipe and their axleback. The whole setup wasn't cheap, but I loooooove the sound.

BMW 135i QuickPower™
http://www.cp-e.com/products/bmw-1m/...power%E2%84%A2

i did the same as you with cp-e. I added the resonator.
I'm not an expert. But if you change the DP you might have a yellow engine light.
you might have to go with some tune to delete that yellow light.

[Gdubz]

Originally Posted by hyper1

i did the same as you with cp-e. I added the resonator.
I'm not an expert. But if you change the DP you might have a yellow engine light.
you might have to go with some tune to delete that yellow light.

Some tunes have an option to block the O2 CEL, or you can get this Can Tool from BMS, which can block/auto-clear it. Friend of mine has a Vishnu catted downpipe on his n55 and still got the O2 CEL, apparently the n55 is super sensitive.

BMS CAN Tool
http://www.**********s.com/BMS-CAN-T...-Z4-35i-X6.htm