# CAT - De-CAT



## Iggy GT-R (Dec 15, 2012)

Just wondering if someone could tell me how may CATs are in the R35?

i'm currently Litchfield Stage 1, but considering just going either full De-Cat or, as long as it'll pass a MOT ok maybe just 1 100/200 cell sports CAT, with a bespoke ECUTEK re-map.

Advice welcome.
Iggy


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## Evo9lution (Aug 24, 2013)

Four. Two primary (downpipes) and two secondary (Y-pipe). Sports cats on the Y-pipe should see you pass the MoT or a roadside sniff test :thumbsup:


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## Iggy GT-R (Dec 15, 2012)

Thanks....The R35 I have is a MY10 M16, so think it came with de-res Milltek Y pipe but not sure if it's DE-CAT.
If not, which would be the easier route, DE-CAT Y pipe or down pipe with with sports CAT it the remaining? Also, which would see the best benefit, if any?

Or does anyone with a M16, know if the Y pipe is DE-CAT?


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## Adamantium (Jun 24, 2002)

Y pipe will be decat.

Easier to do than downpipes. Much better gains from decat downpipes.

Litchfield are working on a high flow cat y pipe from the same people who supply cats for akrapovic oem systems.


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## Chronos (Dec 2, 2013)

ACspeedtech/Russ Fellows do 200 cell sports cat custom y pipes



> Always happy to build custom options, for our 3.5" stainless steel GTR exhaust system we can add in 200 cell sports cats. Running turbo decat downpipes with this system gives a road legal 800hp system with minimal restrictions to flow.


https://www.facebook.com/pages/ACspeedtech/264942290200023


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## Iggy GT-R (Dec 15, 2012)

Adamantium said:


> Y pipe will be decat.
> 
> Easier to do than downpipes. Much better gains from decat downpipes.
> 
> Litchfield are working on a high flow cat y pipe from the same people who supply cats for akrapovic oem systems.


Thanks for that!

I'll be getting Litchfield to do some work in the spring;
Service, circlips, complete sump clean out, solenoid clean, up-rated magnet, possibly a modified bell housing.

So if the Milltek Y pipe I have is de-catted, I might get the down pipes done. Just need to decide if I want 'full de-cat' or 100 cell down pipes!!!


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## Iggy GT-R (Dec 15, 2012)

Ok, i'm new to R35 tuning & can't seem to find an answer with searching.

So i'm only Stage 1 (Litchfield) EcuTek V4.
I'm not really looking to push it much further at the moment, as I only use it as a summer weekend, occasional run & Euro run car.
But i'm considering a bit of exhaust work, but if it doesn't suit i'd retain the OE bits & change back. (moaning old neighbours that really didn't approve of my RB320 & Blitz Nur Spec R exhaust)!
Due to this, i'd be maybe initially looking to pick up second hand parts from someone on here that's either upgrading or putting back to standard!

Is it ok with a Stage 1, with Milltek de-cat Y pipe, to either go fully de-cat downpipe or maybe 100 cell downpipe (MOT reasons) with just a map tweak? If so, with maybe an upgraded panel filer, what power would I be looking at & what db noise level?
Or do I really need the Milltek rear exhaust system which reduces the exhaust back pressure?

Cheers
Iggy


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## Adamantium (Jun 24, 2002)

The y pipe makes the biggest normal difference to back pressure, then the downpipes. The back section has the least silencing in it. Ignoring the downpipes (they are quite a high level mod) putting on a full exhaust usually makes it quieter than just a y-pipe as the stock rear section is quite open and free flowing, and most aftermarkets reduce noise with the back section where's as the stock system is quiet because of the stock y-pipe.

Anders on here made a point of retaining the stock rear section and made I think 620bhp that way. Iain could probably get more out of his now as the mapping has come quite a way since then thanks to the very advanced Rolling road.


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## Adamantium (Jun 24, 2002)

Noise with aftermarket downpipes, y-pipe and stock rear section would be very loud as you'd have no silencing.

If you want a cat for mot purposes you want it in the y-pipe. Aftermarket race cats are metal filament not coated ceramic like factory ones, that's why they are less restrictive and cheaper. It also means they tend to fail by separating from their housings at higher temps hence putting in the y-pipe solves the problem.


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## Iggy GT-R (Dec 15, 2012)

Thanks for the info Adamantium.


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## snuffy (Mar 26, 2014)

Adamantium said:


> The y pipe makes the biggest normal difference to back pressure, then the downpipes. The back section has the least silencing in it. Ignoring the downpipes (they are quite a high level mod) putting on a full exhaust usually makes it quieter than just a y-pipe as the stock rear section is quite open and free flowing, and most aftermarkets reduce noise with the back section where's as the stock system is quiet because of the stock y-pipe.


I was speaking with Amar at SVM this week about getting more noise and that's what he said; i.e. the stock exhaust has very little silencing in it anyway so the only way to get more noise is to have it completely un-silenced. Or if I want more noise then the best idea is to change the downpipes. (plus a remap). I already have a Y-pipe (un-silenced) and find it all very quiet.


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## Bicky8 (Nov 8, 2020)

Getting my bell housing replaced in Litchfield tomorrow morning and was wondering whilst they're doing that is it worth me getting the de cat downpipe and re map to 600bhp installed ??


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## adz87kc (Jan 8, 2018)

Bicky8 said:


> Getting my bell housing replaced in Litchfield tomorrow morning and was wondering whilst they're doing that is it worth me getting the de cat downpipe and re map to 600bhp installed ??


Depends if you want the added noise, smell and MOT hassle that comes with downpipes.

You don't need downpipes for 600hp though.


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## Bicky8 (Nov 8, 2020)

Just want it louder and might get the dump valves also


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## snuffy (Mar 26, 2014)

adz87kc said:


> Depends if you want the added noise, smell and MOT hassle that comes with downpipes.
> 
> You don't need downpipes for 600hp though.


Good point. You can get 600 ponies by changing the exhaust and a remap but keeping the standard downpipes. That's my set up.


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## Bicky8 (Nov 8, 2020)

Do the de cat downpipes make it alot louder yeah ? What would be cheapest option just to make it louder 🤔


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## roberto877 (Sep 12, 2020)

litchfields offer mot for de catted cars no hassle.


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## dudersvr (May 7, 2003)

roberto877 said:


> litchfields offer mot for de catted cars no hassle.


Maybe dont post that on an open forum though !!!


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