Aftermarket midpipe to OE catback question - BMW 1 Series Coupe Forum / 1 Series Convertible Forum (1M / tii / 135i / 128i / Coupe / Cabrio / Hatchback) (BMW E82 E88 128i 130i 135i)

E30 Racer · 09-06-2012, 04:17 PM

Presumably, the post-merge aftermarket pipe diameter is larger than that used by BMW. How does this affect the ability to join them without replacing the coupler on the catback side?

Smiley1175 · 09-06-2012, 06:14 PM

I'm not sure if I fully understand your question but every aftermarket mid pipe I've seen is same diameter and bolts straight on to oe exhaust. The changes are usually the removal of the cats and/or the resonator. Not a change in diameter.
Hope this helps.

E30 Racer · 09-06-2012, 07:55 PM

This is not the case for Akrapovic. The base OD if their gasket (i.e., at the small end of the taper) is nearly as large as the maximum diameter if the OE flange. No way I'd get a reliable seal.

dlai · 09-16-2012, 12:23 PM

It's odd that you have this issue. I found that usually when it's bigger diameter, they end up being tappered down when it gets closer to the flange. Does this happen to your Akrapovic?

E30 Racer · 09-17-2012, 08:39 PM

Quote:

Originally Posted by dlai

It's odd that you have this issue. I found that usually when it's bigger diameter, they end up being tappered down when it gets closer to the flange. Does this happen to your Akrapovic?

Unfortunately that is not the case here. In their defense, I doubt Akrapovic ever intended their midpipe to be used with anything but their axle back exhaust, whose inlet is quite a bit larger than that used by BMW or many aftermarket offerings. Oh well, I'm having Burns Stainless fabricate an adapter.

E30 Racer · 10-19-2012, 10:52 PM

Update: the adapter from Burn Stainless arrived today. I designed the part, sent them the Akra midpipe with a new new graphite sealing gasket, and they fabricated it. As always, their quality was outstanding, with welds that could pass for robotic. Assembly was uneventful, although I'd like to find some springs that will allow me to use the OE flange bolts.

I'll post a sound clip soon, but my initial impression is that cold start, idle, and revving aren't that much louder than stock. Since I haven't actually driven the car, I cannot comment on interior volume at speed or drone yet.

E30 Racer · 10-28-2012, 04:35 PM

On ramps, but the sound is pretty accurate.

ozinaldo · 10-28-2012, 07:54 PM

Quote:

Originally Posted by E30 Racer

On ramps, but the sound is pretty accurate.

Like you've mentioned before what I hear from this clip is not too different than the stock soundwise, just a notch louder. Definitely closer to a N55 mid sound than a Maddad. More burbles.

09-06-2012, 04:17 PM	#1
E30 Racer Private First Class Drives: '11 1M, '99 540i/6, '89 325is Join Date: Aug 2011 Location: Ohio Posts: 177 iTrader: (1)	Aftermarket midpipe to OE catback question Presumably, the post-merge aftermarket pipe diameter is larger than that used by BMW. How does this affect the ability to join them without replacing the coupler on the catback side?
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10-28-2012, 04:35 PM	#7
E30 Racer Private First Class Drives: '11 1M, '99 540i/6, '89 325is Join Date: Aug 2011 Location: Ohio Posts: 177 iTrader: (1)	On ramps, but the sound is pretty accurate. Last edited by E30 Racer; 10-28-2012 at 04:55 PM.

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09-06-2012, 06:14 PM	#2
Smiley1175 Lieutenant Drives: 1M Join Date: Jun 2011 Location: Melbourne Posts: 507 iTrader: (0)	I'm not sure if I fully understand your question but every aftermarket mid pipe I've seen is same diameter and bolts straight on to oe exhaust. The changes are usually the removal of the cats and/or the resonator. Not a change in diameter. Hope this helps.

09-06-2012, 07:55 PM	#3
E30 Racer Private First Class Drives: '11 1M, '99 540i/6, '89 325is Join Date: Aug 2011 Location: Ohio Posts: 177 iTrader: (1)	This is not the case for Akrapovic. The base OD if their gasket (i.e., at the small end of the taper) is nearly as large as the maximum diameter if the OE flange. No way I'd get a reliable seal.

09-16-2012, 12:23 PM	#4
dlai New Member Drives: BMW M3 Join Date: Mar 2011 Location: Australia Posts: 11 iTrader: (0)	It's odd that you have this issue. I found that usually when it's bigger diameter, they end up being tappered down when it gets closer to the flange. Does this happen to your Akrapovic?

10-19-2012, 10:52 PM	#6
E30 Racer Private First Class Drives: '11 1M, '99 540i/6, '89 325is Join Date: Aug 2011 Location: Ohio Posts: 177 iTrader: (1)	Update: the adapter from Burn Stainless arrived today. I designed the part, sent them the Akra midpipe with a new new graphite sealing gasket, and they fabricated it. As always, their quality was outstanding, with welds that could pass for robotic. Assembly was uneventful, although I'd like to find some springs that will allow me to use the OE flange bolts. I'll post a sound clip soon, but my initial impression is that cold start, idle, and revving aren't that much louder than stock. Since I haven't actually driven the car, I cannot comment on interior volume at speed or drone yet.