Is anyone running a fully de-cat standard exhaust ?

4.2 V8 32v Naturally Aspirated - 414 bhp
Dec369
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Is anyone running a fully de-cat standard exhaust ?

Post by Dec369 » Sun Jan 26, 2014 11:06 am

I was thinking about gutting the pre cats & removing the x pipe to add some power & noise. But I am thinking just keep standard x pipe & fully de-cat the exhaust. Anyone done this & have a vidoe of this ???

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Re: Is anyone running a fully de-cat standard exhaust ?

Post by Batfinnk » Sun Jan 26, 2014 12:15 pm

I think just gutting the precats will suffice. Removing the mains will give you a headache every mot time and there is no real benefit to removing them. The pres are the main and biggest restriction. I will be doing min at some point. Does seem a bit of a lottery without a remap as to whether you need to space the O2 sensors though.
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Rw@@dy
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Re: Is anyone running a fully de-cat standard exhaust ?

Post by Rw@@dy » Sun Jan 26, 2014 12:27 pm

I've just had the centre silencer removed and it's perfect. Just enough noise with the valves open, quiet when not. I am going to get the pre cats done too at some point but heard this is mainly for extra power rather than noise

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Re: Is anyone running a fully de-cat standard exhaust ?

Post by Dec369 » Sun Jan 26, 2014 12:39 pm

I would be getting a remap with getting the cats done but just wondered if I would get the same noise with gutting the cats save doing the x pipe. It's noise & a bit more power I am after. In total I was thinking about gutting cats, remap & cold air feed

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Re: Is anyone running a fully de-cat standard exhaust ?

Post by Batfinnk » Sun Jan 26, 2014 12:47 pm

You will naturally get more noise from gutting the pre cats because you are removing a restriction in the system which means faster air flow and more noise out the back. The cold air feed won't add any major power gains but should give you more induction noise depending on which one you go for.
Current car: 2007 BMW 530d touring.
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Re: Is anyone running a fully de-cat standard exhaust ?

Post by Dec369 » Sun Jan 26, 2014 12:57 pm

Batfinnk wrote:You will naturally get more noise from gutting the pre cats because you are removing a restriction in the system which means faster air flow and more noise out the back. The cold air feed won't add any major power gains but should give you more induction noise depending on which one you go for.

I will probably just go for the pre cats then :) see how loud they make it & if I want more do the x pipes. I am just going for standard air box but remove the aux rad & do it that way. Hopefully won't heat soak as much & it seemed to do on the dyno last time

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Re: Is anyone running a fully de-cat standard exhaust ?

Post by m14rrv » Sun Jan 26, 2014 2:14 pm

Does eml light come on if you gut pre cats? I would of thought it wouldn't as it's still got the second cats in place
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Re: Is anyone running a fully de-cat standard exhaust ?

Post by Dec369 » Sun Jan 26, 2014 2:26 pm

m14rrv wrote:Does eml light come on if you gut pre cats? I would of thought it wouldn't as it's still got the second cats in place
Yeh I believe it does as there will be a O2 sensor in the precats also I presume, but with a map it clears any lights or warnings. I was also told that when pre cats are gutted tho loose the 5.5k kick so need to map it back in

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Re: Is anyone running a fully de-cat standard exhaust ?

Post by Rick_RS4 » Sun Jan 26, 2014 8:57 pm

the lambda spacer goes in after the cats not before,

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Re: Is anyone running a fully de-cat standard exhaust ?

Post by Batfinnk » Sun Jan 26, 2014 9:07 pm

Plus I may be wrong but don't think the 5.5 kick has anything to do with the exhaust. I'm sure it on the intake side?
Current car: 2007 BMW 530d touring.
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Re: Is anyone running a fully de-cat standard exhaust ?

Post by Dec369 » Sun Jan 26, 2014 10:22 pm

Rick_RS4 wrote:the lambda spacer goes in after the cats not before,
There is already a sensor in there though

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Re: Is anyone running a fully de-cat standard exhaust ?

Post by Dec369 » Sun Jan 26, 2014 10:23 pm

Batfinnk wrote:Plus I may be wrong but don't think the 5.5 kick has anything to do with the exhaust. I'm sure it on the intake side?
I was told it was something to do with the back pressure in the exhaust but I am not 100% sure haha

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Re: Is anyone running a fully de-cat standard exhaust ?

Post by Rick_RS4 » Sun Jan 26, 2014 11:44 pm

Dec369 wrote:
Rick_RS4 wrote:the lambda spacer goes in after the cats not before,
There is already a sensor in there though

yes the first one reads the gasses the engine is making, the second one reads them after they have been through the cats, if the second one senses more flow ( due to cat gutting) it throws a cel, so you space it so its not in the exhaust flow, so no cell

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Re: Is anyone running a fully de-cat standard exhaust ?

Post by m14rrv » Mon Jan 27, 2014 9:18 pm

Is any one running spacers on the 2nd sensors? If so what spacers you running
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Re: Is anyone running a fully de-cat standard exhaust ?

Post by Covkiller » Mon Feb 03, 2014 10:09 pm

I run a full non res valved, cat bypass Milltek system. Valves closed quieter than with cats, S button valves open = gods thunder, screams its bolx off at 8k revs in 3rd.
Absolutely 100% love it and recommend it. More HP and Torque see the following thread:

https://www.facebook.com/media/set/?set ... 49.1548228
:nogarors4:
RS4 B7, Mugello Blue, K&W V3 & HR ARBs, set up by Centre Gravity, Milltek Valved Non Res & cat bypass pipes, BMC air filter, braided hoses, DOT 5.1, Terraclean, MRC Full Carbon Clean, MRC remap 448PS 477NM, 20" S7 alloys with 4mm spacers & Hawke spigots 66.6 > 57.1, AP Racing front discs. Sold Sept 2019. Now rocking an F80 M3

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