# Hi Flow Sports Cat or Decat? Exhaust time!



## Phil-TT (Feb 11, 2011)

It looks like I am about to acquire Non resonated Milltek cat back exhaust system for the car. However I have been told to get the best out of this and get maximum gains from it, I should be looking to run a Hi Flow sports cat aswell, however these things cost like £600 and I can't afford that on top of the price of the exhaust and would struggle to justify that.

The option I intended to take was that of decat. I know I could have one made up for likely around £100. But am aware that there is the likelihood of my car failing the MOT on account of the decat. However, my question remains, will a decat bring as much benefit as a hi flow (legal) sports cat, surely nothing can allow a better air flow than a straight pipe? Also are there any less costly options as far as the sports cats go? I am also completely ignorant to the role of the downpipe and the benefits of changing that, so help there would be great too.

Cheers


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## neilc (Aug 8, 2011)

Well I have got a 100 cell sports cat on mine which i'm sure from previous threads is slightly slower spolling than a decat but obviously no hassle at MOT time. And cost wise yes they are very expensive about £600.00 is right.


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## tony_rigby_uk (Nov 27, 2008)

sports cat on mine also... maybe a decat would be ok.. but getting the sports cat hott enough for the MOT is hard enough..


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## crapgolf (Jul 12, 2009)

Hi,

Decat on mine great value for money may be sale soon if you want to make me an offer?

Crapgolf.


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## Phil-TT (Feb 11, 2011)

What about the performance gains from the sports cats guys? Make a big difference?


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## neilc (Aug 8, 2011)

MUFC.TT said:


> What about the performance gains from the sports cats guys? Make a big difference?


Mines a BT car so was essential on mine but not sure what difference it will make to your car but you would imagine considerable. A standard cat is 300 cells I believe so going down to 100 has got to make it flow much better.


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## Phil-TT (Feb 11, 2011)

That's what I would have expected mate. The decat is then likely to offer a similar thing isn't it? Just with the MOT hassle.


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## neilc (Aug 8, 2011)

MUFC.TT said:


> That's what I would have expected mate. The decat is then likely to offer a similar thing isn't it? Just with the MOT hassle.


You got it.


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## Phil-TT (Feb 11, 2011)

Given the difference in price I would be tempted to go decat and just see what way things work out. Undecided as of yet. Do the sports cats affect the noise level too?


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## T3RBO (Dec 9, 2003)

neilc said:


> A standard cat is 300 cells I believe so going down to 100 has got to make it flow much better.


Think it's 400 cell


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## jamman (May 6, 2002)

Phil you will see gains with either a sports cat or a decat but dont expect massive gains because you simply wont get them remember you will still be starting your system with the OEM downpipe.


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## T3RBO (Dec 9, 2003)

I would just fit the cat back now and save for the downpipe, sports cat and remap tweak at a later date :wink:


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## jamman (May 6, 2002)

T3RBO said:


> I would just fit the cat back now and save for the downpipe, sports cat and remap tweak at a later date :wink:


Im giving Robb the dreaded +1


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## Phil-TT (Feb 11, 2011)

I think I will probably fit the decat while I save up for the downpipe and sports cat. Not going to cost a massive amount.

What gains would I expect with decat+exhaust with OEM downpipe and with new downpipe+sports cat+exhaust?

Also, will a decat make any warning lights or anything come on? That would do my head in. Will I only need a remap once the DP is fitted, I will be ok without it running the Milltek and the decat?


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## Ginn L (Aug 24, 2009)

Sorry to keep this thread bumped.

This may sound like a ridiculous question, but would the exhaust back fire, from fitting a decat down pipe with a Milltek resonated cat-back?

I considered doing this to mine, but the only thing that puts me off is the dreaded popping and banging. I don't want unwanted attention from the Police, that's all.

A friend of mine had a decat on his A3 1.8T, with some cheap shite 3" exhaust. And it popped like shit in every gear, even at like 2k RPM. It sounded well, but I want something more subtle.

I would have my map adjusted to suit the decat by the way, if that affects anything.


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## Rich196 (Mar 31, 2011)

I like a popping exhaust on over run, there is a mini copper S round me, with the twin little center exhausts that pops changing gear and lifting off the throttle, how do you make this happen? its not backfiring and its not loud I just love the sound. It like a very subtle rally car


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## jamman (May 6, 2002)

MUFC.TT said:


> I think I will probably fit the decat while I save up for the downpipe and sports cat. Not going to cost a massive amount.
> 
> What gains would I expect with decat+exhaust with OEM downpipe and with new downpipe+sports cat+exhaust?
> 
> Also, will a decat make any warning lights or anything come on? That would do my head in. Will I only need a remap once the DP is fitted, I will be ok without it running the Milltek and the decat?


5-10 bhp MAX

Yep decat will cause warning light it will need to be mapped out or a spacer fitted :wink:


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## Phil-TT (Feb 11, 2011)

What do you mean by a spacer James? Won't be having anything that causes an error light, they do my head in!

With regards to people talking about exhausts popping, I think it's great as long as it isn't insanely loud!


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## AmpTThill (Sep 18, 2011)

If your changing the cat then you should also change the downpipe. I think the downpipe is the most restrictive part in the whole zorst so chaning that for a 3" will give the most gain + quicker spool. The engine management light comes on due to emissions. Remap will sort this out (or drill the bulb out... joke) 

I went for pipewerx 3"dp + decat. Couldn't be happier.


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## Phil-TT (Feb 11, 2011)

How much did your DP cost you mate? I am finding it hard to justify this now without the DP, but I can't bring my car to Awesome or VagCheck etc because I am in N.I and dont trust the mappers here.


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## AmpTThill (Sep 18, 2011)

£360 from awesome http://www.awesome-gti.co.uk/product.php?xProd=27527&xSec=460

Good price, service wasn't bad either


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## Phil-TT (Feb 11, 2011)

Did they do your remap aswell mate? It would seem I have opened a can of worms on myself here...


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## AmpTThill (Sep 18, 2011)

Not had it remapped yet. Going to fit my TIP first then stage 2 time [smiley=guitarist.gif]

Not going to leave it long, engine light annoys me too...


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## AmpTThill (Sep 18, 2011)

Awesome a bit far for me - TT shop are local in Bedford.

If your down south could do a group stage 2 remap :idea:


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## TT51 (Feb 28, 2009)

My car had a standard dp, decat and resonated miltek with a Vagcheck stage 2. No pops or bangs but a nice deep but not noisy tone with a few burbles. Spool up was very quick and the car pulled like a train.

Engine light comes on but liquid gauge to reset or you can have it mapped out. A spacer is exactly what it's called, spaces the O2 sensor further away from the exhaust gas flow


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## Phil-TT (Feb 11, 2011)

Can you buy a spacer to fit when installing the decat and exhaust? I don't have the money for the dp tbh.


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## Rich196 (Mar 31, 2011)

MUFC.TT said:


> Can you buy a spacer to fit when installing the decat and exhaust? I don't have the money for the dp tbh.


Check this out mate:

http://www.awesome-gti.co.uk/product.php?xProd=32887&xSec=460


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## Phil-TT (Feb 11, 2011)

So that with a decat and my Milltek should stop my warning lights coming on?


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## T3RBO (Dec 9, 2003)

If your not changing the downpipe then the below decat is what you need, and yes with spacer no light on

http://www.awesome-gti.co.uk/product.ph ... 2&xSec=460


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## Ginn L (Aug 24, 2009)

TT51 said:


> My car had a standard dp, decat and resonated miltek with a Vagcheck stage 2. No pops or bangs but a nice deep but not noisy tone with a few burbles. Spool up was very quick and the car pulled like a train.
> 
> Engine light comes on but liquid gauge to reset or you can have it mapped out. A spacer is exactly what it's called, spaces the O2 sensor further away from the exhaust gas flow


Just what I wanted to hear, think I've made my mind up now 

I think the backfiring can sound good, if its not too loud, but I'd rather not have it just because it gives the police a reason to pull you up, and potentially find out you have a decat. :lol:


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## Phil-TT (Feb 11, 2011)

So if I go ahead and buy my Milltek system and decat, running the OEM DP, then fit that spacer I should have a bit of extra performance and no warning light?

How is the spacer fitted?


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## BAMTT (Feb 22, 2004)

You may want to find out if the ECU can control the boost well enough to prevent spikes if you are not going to map it,


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## Phil-TT (Feb 11, 2011)

A new issue :lol: What do you mean BAM? My understanding of this isn't huge and I wasn't aware that this would cause any issues, its looking increasingly like I am just going to have to fit the Milltek system and leave the original cat and DP.


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## Rich196 (Mar 31, 2011)

BAM is an engine type, the 1.8T came in BAM and APX, APX are in the older TT's


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## Phil-TT (Feb 11, 2011)

Rich196 said:


> BAM is an engine type, the 1.8T came in BAM and APX, APX are in the older TT's


Cheers Rich, but what I actually meant was what did that guy with the username BAMTT mean :lol: , he said something about spiking and I didn't understand that and just shortened his name to BAM when asking him the question. The engine types were one of the few things I already knew about :lol: :lol:


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## Danny1 (Sep 2, 2010)

He means the cars ECU will be looking for a cat in your system, so without a remap, the ecu trying to run the car with no cat could cause other running problems like jerky acceleration, boost spikes etc, i dont know if this will happen just giving a simple versionish of what BAM was saying.


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## Adam-tt (Apr 3, 2010)

I never had that problem on my bam engine

Sent from my Atari 2600


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## Phil-TT (Feb 11, 2011)

Is your car not mapped Adam? Anybody else got experience with decat on a non mapped car?


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## Adam-tt (Apr 3, 2010)

i had just a decat before it was mapped i had no problems apart from the engine light coming on, you wont see a massive difference really but the turbo will spool slightly quicker


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## Phil-TT (Feb 11, 2011)

With the decat and Milltek I won't see any real gains? I am going to buy that spacer from Awesome to try and prevent the warning light issue, that would do my head in.


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## Adam-tt (Apr 3, 2010)

being honest without a remap to go with it, no you wont see much of a gain
the spacer works a treat i have a few friends who run them


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## Phil-TT (Feb 11, 2011)

How is the spacer fitted mate?


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## Adam-tt (Apr 3, 2010)

instead of being like this where the sensor would sit in the flow of the fumes









the spacers keeps the sensor away for the fumes


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## tony_rigby_uk (Nov 27, 2008)

REVO STAGE 2 MAP will remove the emissions light.


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## AmpTThill (Sep 18, 2011)

Agree with Adam, you need the remap to feel the gain. Bit like buying a pair of football boots to walk the dog... Maybe :?

Mine is not mapped yet and i have no issues (apart from engine light but I'm not using a spacer).


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## Phil-TT (Feb 11, 2011)

I will get round to the remap eventually, but will have to make do for the time being.


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## BAMTT (Feb 22, 2004)

Sorry I didn't reply, i don't have a great deal of internet access, but yes by removing the cat you lose fair amount of restriction, maybe this is more of an issue on cars with larger turbos, as when I decatted my Impreza to a full 3" system I was specifically told to stay off boost but then the IHI vf35 is a bit surgey anyway

As for the MOT you just need to find a 'friendly' garage


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