Rear CAT Delete with RPI?

wspohn · 11-13-2019, 11:27 AM

My coupe runs the RPI rear set up and I don't find it to be too loud. That may be because I don't mind a good sounding if somewhat loud exhaust note (as long as there is little drone in a closed car), or possibly the RPI cans have broken in and gotten a bit quieter than they would have been when first installed (I have heard that this happens - true?).

Apparently the secondary CAT presents significant exhaust back pressure. I had thought of removing it or just gutting it, but wondered if anyone had actual experience with this, using RPI or similarly 'sporty' (i.e. a bit loud) exhaust boxes at the rear?

86Zed · 11-13-2019, 12:12 PM

My friend tracks his Z4MC and went full catless on the car with the RPI mufflers to the tune of 104+ dB that posed issues at a few of the local tracks where limits are generally <100dB.

I do not recall if he did an intermediate setup with one set of cats still on the car. Either way, the car runs straight pipes back to the stock mufflers now and its loud but not as extreme.

On the bit about exhaust components "breaking in"- my Stromung exhaust increased in volume after a few months, has stayed there ever since. I do not know of any instances where a car gets quieter.

ga41 · 11-15-2019, 04:14 AM

I've had RPI's for several years now for a mostly daily driven car. I think it did get a bit quieter after some time but it's been so long ago really that it may just be getting used to them.

First time i ever heard of someone saying they're not loud enough though!!

RossBMWZseries · 11-19-2019, 03:56 PM

This is true. When I first installed my RPI's, the car sounded gloriously loud. I captured the sound of it after 3 days of driving around and it sounded loud in video too. Now, it doesn't sound as loud when revving and also in video, sounds a bit more tamed.

This is the only exhaust that I know of for the M that seems to get quieter within time. Not to say it's a quiet exhaust. It's still the loudest of them all.

I do have Euro catless headers, DKF S pipe with race cats but changing them to resonators as soon as the car is out the shop. I'm also swapping the stock X pipe for a straight through X pipe with no resonator. I want it louder and preferably to spit flames once I get it tuned.

rockstar93 · 11-19-2019, 04:05 PM

The exhaust isn't getting quieter, we're just going deaf

I'm happy with my setup of Fabspeed (catless) headers, stock US-spec section 1 (which I believe have smaller cats than the Euro-spec), stock X-pipe, and RPi 'mufflers'.

But it is loud.

XMetal · 11-19-2019, 04:46 PM

Quote:

Originally Posted by rockstar93

The exhaust isn't getting quieter, we're just going deaf

I'm happy with my setup of Fabspeed (catless) headers, stock US-spec section 1 (which I believe have smaller cats than the Euro-spec), stock X-pipe, and RPi 'mufflers'.

But it is loud.

What? What did you say??? I can't hear you

Most people say exhaust "break-in" as they age and gets quieter, but I think they're either getting used to the noise, or their ears lost a few dBs in sensitivities. Think about this for a moment. As the mufflers age, more of the sound deadening fiberglass materials get burnt off, which means it should get louder, not less.

RossBMWZseries · 11-19-2019, 07:14 PM

Haha perhaps, Rockstar has a valid point, however, people that haven’t heard my car in a while also say it sounds quieter than it did when I got the cans installed. I could literally see the fiberglass materials being burned off and once gone, it didn’t sound the same. Also, my hearing seems to be as good as new based on the recent government hearings tests I’ve had. Only way to test this is to use a dB decibel meter

11-13-2019, 11:27 AM	#1
wspohn Private 79 Rep 93 Posts Drives: 2007 Z4MC Join Date: Apr 2010 Location: Vancouver BC iTrader: (0)	Rear CAT Delete with RPI? My coupe runs the RPI rear set up and I don't find it to be too loud. That may be because I don't mind a good sounding if somewhat loud exhaust note (as long as there is little drone in a closed car), or possibly the RPI cans have broken in and gotten a bit quieter than they would have been when first installed (I have heard that this happens - true?). Apparently the secondary CAT presents significant exhaust back pressure. I had thought of removing it or just gutting it, but wondered if anyone had actual experience with this, using RPI or similarly 'sporty' (i.e. a bit loud) exhaust boxes at the rear?
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11-13-2019, 12:12 PM	#2
86Zed Get off my lawn 932 Rep 1,158 Posts Drives: 6MT Join Date: Sep 2015 Location: USA iTrader: (7) Garage List 2023 GR Corolla [0.00] 2022 BMW X3 M40i [10.00] 2007 BMW Z4M Coupe [0.00] 2002 BMW 325xiT [0.00] 1991 BMW 318is [0.00]	My friend tracks his Z4MC and went full catless on the car with the RPI mufflers to the tune of 104+ dB that posed issues at a few of the local tracks where limits are generally <100dB. I do not recall if he did an intermediate setup with one set of cats still on the car. Either way, the car runs straight pipes back to the stock mufflers now and its loud but not as extreme. On the bit about exhaust components "breaking in"- my Stromung exhaust increased in volume after a few months, has stayed there ever since. I do not know of any instances where a car gets quieter.
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11-15-2019, 04:14 AM	#3
ga41 Lieutenant 31 Rep 503 Posts Drives: Z4 M Coupe Join Date: Jun 2009 Location: Paphos iTrader: (0) Garage List 2006 Z4 M Coupe [0.00]	I've had RPI's for several years now for a mostly daily driven car. I think it did get a bit quieter after some time but it's been so long ago really that it may just be getting used to them. First time i ever heard of someone saying they're not loud enough though!! __________________
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11-19-2019, 03:56 PM	#4
RossBMWZseries Major 224 Rep 1,130 Posts Drives: '11 E92 328i LCI & '06 Z4MR Join Date: Jun 2014 Location: San Juan TX iTrader: (1) Garage List 2006 BMW Z4M Roadster [7.00]	This is true. When I first installed my RPI's, the car sounded gloriously loud. I captured the sound of it after 3 days of driving around and it sounded loud in video too. Now, it doesn't sound as loud when revving and also in video, sounds a bit more tamed. This is the only exhaust that I know of for the M that seems to get quieter within time. Not to say it's a quiet exhaust. It's still the loudest of them all. I do have Euro catless headers, DKF S pipe with race cats but changing them to resonators as soon as the car is out the shop. I'm also swapping the stock X pipe for a straight through X pipe with no resonator. I want it louder and preferably to spit flames once I get it tuned. __________________ 2014 BMW X5 Sdrive35i F15 2011 BMW 328i E92 LCI 2006 BMW Z4 M Roadster E85 2013 BMW S1000RR K46 R.I.P. 1998 BMW Z3 Roadster 1.9L E36 SOLD
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11-19-2019, 04:05 PM	#5
rockstar93 Lieutenant 321 Rep 528 Posts Drives: E86 Z4MC; E92 M3 Join Date: Jun 2015 Location: Cambridge, Ontario iTrader: (8) Garage List 2011 BMW E92 M3 [0.00] 2006 BMW Z4M Coupe [0.00]	The exhaust isn't getting quieter, we're just going deaf I'm happy with my setup of Fabspeed (catless) headers, stock US-spec section 1 (which I believe have smaller cats than the Euro-spec), stock X-pipe, and RPi 'mufflers'. But it is loud. __________________ E46 M3 Coupe 6MT Jet Black/Cinnamon GONE E85 Z4M Roadster Imola Red/Black GONE E90 M3 Sedan 6MT Jerez Black/Fox Red GONE E86 Z4M Coupe Interlagos Blue/Black E92 M3 Coupe 6MT Interlagos Blue/Fox Red - Build Thread
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11-19-2019, 07:14 PM	#7
RossBMWZseries Major 224 Rep 1,130 Posts Drives: '11 E92 328i LCI & '06 Z4MR Join Date: Jun 2014 Location: San Juan TX iTrader: (1) Garage List 2006 BMW Z4M Roadster [7.00]	Haha perhaps, Rockstar has a valid point, however, people that haven’t heard my car in a while also say it sounds quieter than it did when I got the cans installed. I could literally see the fiberglass materials being burned off and once gone, it didn’t sound the same. Also, my hearing seems to be as good as new based on the recent government hearings tests I’ve had. Only way to test this is to use a dB decibel meter
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