Custom Mid-Pipe Help

Cozy · 09-11-2012, 04:41 AM

Hi all,

I need some knowledge on the piping diameter of the stock exhaust system on the 135i so I can have some custom mid-pipes built to suit. From what I can tell via search & Google is that the dual down pipes are 2.5" ID each, connecting to dual mid-pipes that are 2.25" ID each, these then connect at the flange (after the resonator) to either a 2.5" or 3" ID stock axle back, can anyone confirm this?

What I want to do is build my exhaust in stages as I'm not sure where I'm going with it right now and money is also spread over suspension components too. Deleting the Cats in the mid-pipes should help the car breathe a little better and release a little more sound for me. The plan is to fit AR DP's (which I believe are 3" ID each, right?) to custom mid-pipes, then either a custom axle back or BMW PE. The reason I am choosing custom mid-pipes rather than N55 mids or Cat cut-out on N54 mids is so I can increase the pipe size slightly & have two small resonators put in as replacements for the Cats they'll take out, this should control drone and rasp (especially with PE).

Another reason why I am choosing to do it this way is that the custom-mid pipes will have to be modelled on the stock mid-pipes so that they connect to the stock axle-back and stock DP's, this leaves me with a completely interchangable mid-section should I need to swap in the secondary Cats again. It also means that the BMW PE will connect right up if I go that way and I'll not need to use the Y-Pipe, I can install on my driveway in this case.

So that I don't choke the system, I think that dual 2.5" or 2.75" ID mid-pipes would work well with other stock components for the time being. That's if the measurements I've found are correct. What I don't want to do is decrease the diameter at any point and also as the car is now tuned, stepping up 0.25" - 0.5" in the mid-pipes won't hurt it and will make the car 'ready' for larger aftermarket DP's without introducing a choke point.

Can anyone forsee any problems with the pipe size I plan to use i.e. is there a restriction on space under there? I notice that HPF use a single 3" pipe, I guess their reason for not using dual 3" was space limitation.

Thanks

brusk · 09-11-2012, 07:19 AM

It really sounds like your overthinking things and creating a headache for yourself. There a several affordable resonated midpipes on the market that will do what your looking for. I looked into making my own and after pricing the piping, flanges, gaskets, resonators and paying a little back for welding gas and wear and tear on the welder it wasn't enough difference to justify the time spent. Since the pipes come together and reduce down to a 3" going bigger on the mids isn't going to give you anything. HPF uses a 3.5" and I beleive most of that is for weight reduction but space is an issue. Even with most after market dual 2.5" mids there's spacing issues with the brace and it needs spaced down.

Cozy · 09-11-2012, 08:18 AM

Thanks for the reply.

I won't be fabricating the mid-pipes myself, I local shop will be doing this for me with two small inline resonators. I'm in the UK and we have don't have any options for the mid-pipes and only 2 or 3 choices for the axle-back & DP's...we're a way behind the USA when it comes to an established e9x/e8x tuning market. I've looked into importing Berk or Maddad resonated mid-pipes from the USA but it seems that we don't have a decent trade link at all, to put that into perspective a set of Berk mid-pipes would land at my door for around $1100 after taxes.

So, here we are, custom or go home really

.

1911A145 · 09-11-2012, 07:57 PM

No need to go 2.5 or bigger on the mids. remember there is two of them and there isnt much power to be gained by going larger on this car. also, if you do go bigger, you will have to use spacers to bring down the bar and you will go crazy trying to fit a resonator in there with the increased piping size and the limited room. you will have to stagger them and even then the resonators you buy will have to be so small I doub you will notice any sound or rasp difference. The cat-back isnt as restrictive as you think it is and until you are full bolt on with meth running 100 octane race tune I doubt youll notice much difference either and only create more bark then bite. do the catless downpipes, get rid of the cats in the mids, leave everything else alone unless you want to draw attention... just my .02 cents.

Cozy · 09-12-2012, 02:47 AM

Thanks

So 2.5" is realistically the maximum I should use. I think that's pretty much standard piping size across most custom fabricators so that'll be no problem. I will have to stick in some resonators as I've heard a BMW PE with catless DP's and N55 mids and it sounds too raspy for me, I will pretty much have the Berk mids replicated if possible. I agree the axle-back is mostly for noise but a great noise so I'd be foolish to miss out on it.

I believe another member on here went the route I plan on, RaihaX. I also remember him saying that his PE was really raspy until he resonated the mid-pipes.

brusk · 09-12-2012, 07:28 AM

That sucks shipping is so much I assumed there would be more choices for you. might be easier to cut the cats out of your mids (assuming your N54) and weld in resonators in their place.

Cozy · 09-13-2012, 09:11 AM

That'd definitely be the cheapest option but I want to keep my stock-mids to swap back in. We have a yearly smog check that the car needs to pass so it looks like I'm stuck with a custom setup.

135Pats · 09-13-2012, 10:01 AM

Quote:

Originally Posted by JamJay

That'd definitely be the cheapest option but I want to keep my stock-mids to swap back in. We have a yearly smog check that the car needs to pass so it looks like I'm stuck with a custom setup.

I may be stating the obvious, but even with the stock mids you will likely fail emissions testing, assuming your downpipes are catless. Im not sure how stringent the test is in the UK, but here the secondary cats wont save you if youre catless with the DPs. Perhaps consider gutting the n54 mids, and when its testing time swap back the OE downpipes?

Cozy · 09-13-2012, 10:05 AM

Our emissions limits aren't too low to be truthful and it's been confirmed on 335i's (where tuning is more popular here) that the stock mids pass the test. I will be going for catless DPs so the fact that the mids pass our checks really is a saviour as changing the DP's I hear is a tough job. I know for a fact that I could not perform a DP swap myself so each year I'd have to pay a chunck of money for the swap.

09-11-2012, 04:41 AM	#1
Cozy Major 113 Rep 1,487 Posts Drives: E82 135i Join Date: Mar 2011 Location: Surrey, England iTrader: (0)	Custom Mid-Pipe Help Hi all, I need some knowledge on the piping diameter of the stock exhaust system on the 135i so I can have some custom mid-pipes built to suit. From what I can tell via search & Google is that the dual down pipes are 2.5" ID each, connecting to dual mid-pipes that are 2.25" ID each, these then connect at the flange (after the resonator) to either a 2.5" or 3" ID stock axle back, can anyone confirm this? What I want to do is build my exhaust in stages as I'm not sure where I'm going with it right now and money is also spread over suspension components too. Deleting the Cats in the mid-pipes should help the car breathe a little better and release a little more sound for me. The plan is to fit AR DP's (which I believe are 3" ID each, right?) to custom mid-pipes, then either a custom axle back or BMW PE. The reason I am choosing custom mid-pipes rather than N55 mids or Cat cut-out on N54 mids is so I can increase the pipe size slightly & have two small resonators put in as replacements for the Cats they'll take out, this should control drone and rasp (especially with PE). Another reason why I am choosing to do it this way is that the custom-mid pipes will have to be modelled on the stock mid-pipes so that they connect to the stock axle-back and stock DP's, this leaves me with a completely interchangable mid-section should I need to swap in the secondary Cats again. It also means that the BMW PE will connect right up if I go that way and I'll not need to use the Y-Pipe, I can install on my driveway in this case. So that I don't choke the system, I think that dual 2.5" or 2.75" ID mid-pipes would work well with other stock components for the time being. That's if the measurements I've found are correct. What I don't want to do is decrease the diameter at any point and also as the car is now tuned, stepping up 0.25" - 0.5" in the mid-pipes won't hurt it and will make the car 'ready' for larger aftermarket DP's without introducing a choke point. Can anyone forsee any problems with the pipe size I plan to use i.e. is there a restriction on space under there? I notice that HPF use a single 3" pipe, I guess their reason for not using dual 3" was space limitation. Thanks Last edited by Cozy; 09-11-2012 at 04:50 AM..
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09-11-2012, 07:19 AM	#2
brusk Lieutenant 33 Rep 578 Posts Drives: 2008 135i Coupe Join Date: Jan 2012 Location: Cleveland, TN iTrader: (1)	It really sounds like your overthinking things and creating a headache for yourself. There a several affordable resonated midpipes on the market that will do what your looking for. I looked into making my own and after pricing the piping, flanges, gaskets, resonators and paying a little back for welding gas and wear and tear on the welder it wasn't enough difference to justify the time spent. Since the pipes come together and reduce down to a 3" going bigger on the mids isn't going to give you anything. HPF uses a 3.5" and I beleive most of that is for weight reduction but space is an issue. Even with most after market dual 2.5" mids there's spacing issues with the brace and it needs spaced down. __________________ 2008 135i - MHD/JB4, MS DP's, AMS IC, UI CAI, CDV delete, M3 control arms/Links, RE Toe Link, ECS Trailing Arm, M3 rear SF & Trans bushings, SS brake lines, Michelin PSS.
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09-11-2012, 08:18 AM	#3
Cozy Major 113 Rep 1,487 Posts Drives: E82 135i Join Date: Mar 2011 Location: Surrey, England iTrader: (0)	Thanks for the reply. I won't be fabricating the mid-pipes myself, I local shop will be doing this for me with two small inline resonators. I'm in the UK and we have don't have any options for the mid-pipes and only 2 or 3 choices for the axle-back & DP's...we're a way behind the USA when it comes to an established e9x/e8x tuning market. I've looked into importing Berk or Maddad resonated mid-pipes from the USA but it seems that we don't have a decent trade link at all, to put that into perspective a set of Berk mid-pipes would land at my door for around $1100 after taxes. So, here we are, custom or go home really .
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09-11-2012, 07:57 PM	#4
1911A145 Captain 34 Rep 770 Posts Drives: 135i Join Date: Mar 2012 Location: Port Saint Lucie, FL iTrader: (4)	No need to go 2.5 or bigger on the mids. remember there is two of them and there isnt much power to be gained by going larger on this car. also, if you do go bigger, you will have to use spacers to bring down the bar and you will go crazy trying to fit a resonator in there with the increased piping size and the limited room. you will have to stagger them and even then the resonators you buy will have to be so small I doub you will notice any sound or rasp difference. The cat-back isnt as restrictive as you think it is and until you are full bolt on with meth running 100 octane race tune I doubt youll notice much difference either and only create more bark then bite. do the catless downpipes, get rid of the cats in the mids, leave everything else alone unless you want to draw attention... just my .02 cents.
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09-12-2012, 02:47 AM	#5
Cozy Major 113 Rep 1,487 Posts Drives: E82 135i Join Date: Mar 2011 Location: Surrey, England iTrader: (0)	Thanks So 2.5" is realistically the maximum I should use. I think that's pretty much standard piping size across most custom fabricators so that'll be no problem. I will have to stick in some resonators as I've heard a BMW PE with catless DP's and N55 mids and it sounds too raspy for me, I will pretty much have the Berk mids replicated if possible. I agree the axle-back is mostly for noise but a great noise so I'd be foolish to miss out on it. I believe another member on here went the route I plan on, RaihaX. I also remember him saying that his PE was really raspy until he resonated the mid-pipes.
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09-12-2012, 07:28 AM	#6
brusk Lieutenant 33 Rep 578 Posts Drives: 2008 135i Coupe Join Date: Jan 2012 Location: Cleveland, TN iTrader: (1)	That sucks shipping is so much I assumed there would be more choices for you. might be easier to cut the cats out of your mids (assuming your N54) and weld in resonators in their place. __________________ 2008 135i - MHD/JB4, MS DP's, AMS IC, UI CAI, CDV delete, M3 control arms/Links, RE Toe Link, ECS Trailing Arm, M3 rear SF & Trans bushings, SS brake lines, Michelin PSS.
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09-13-2012, 09:11 AM	#7
Cozy Major 113 Rep 1,487 Posts Drives: E82 135i Join Date: Mar 2011 Location: Surrey, England iTrader: (0)	That'd definitely be the cheapest option but I want to keep my stock-mids to swap back in. We have a yearly smog check that the car needs to pass so it looks like I'm stuck with a custom setup.
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09-13-2012, 10:05 AM	#9
Cozy Major 113 Rep 1,487 Posts Drives: E82 135i Join Date: Mar 2011 Location: Surrey, England iTrader: (0)	Our emissions limits aren't too low to be truthful and it's been confirmed on 335i's (where tuning is more popular here) that the stock mids pass the test. I will be going for catless DPs so the fact that the mids pass our checks really is a saviour as changing the DP's I hear is a tough job. I know for a fact that I could not perform a DP swap myself so each year I'd have to pay a chunck of money for the swap.
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