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Mk5 R32 - Decat?

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#1
sixteen10

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Hi All

Hopefully you guys can help here as the responses I got on the VW Vortex were a little sad to say the least. I was wondering what affect decatting a mk5 R32 has? I asked on the Vortex and didn't get much response to say if doing this has any positive or negative impacts on the vehicle

After doing so and being slightly upset at the power gains everyone creeped out of the woodwork and then stated things like " I didn't wanna say it but doing the decat is probably causing you some lost ponies"
Would have been nicer to hear it before I did the mod but anyway , perhaps on the proper R32 forum someone may have a better response for me.

Anyways , here is the stock dyno ( with GruppeM intake only ) Bear in mind the dyno was done with 95 RON and at near 1.2 miles above sea level.:

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Then I cut out the cats , replaced them with test pipes ( straight piping in OEM size ) and then fitted my Milltek Resonated system and dyno'd again , this is with the intake , exhaust , de-cat and OEM software :

Posted Image

2.5wkw and almost 9Nm over stock. I expected to see at least 5wkw but then again maybe the exhaust does nothing for power gains with OEM software?

The car feels much better on the road and is far more eager to go especially at lower rpm which is evident on the graph but with the later responses on the VW Vortex I am now concerned maybe I was too hasty in cutting out the cats?

TIA :)

Edited by sixteen10, 14 June 2011 - 01:08 PM.


#2
sixteen10

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Ok to add :

1. I've done further searching but it seems there is not much info readily available regarding decatting the mk5 R32.

2. Since I have done it I have had no CEL errors at all , I haven't scanned her with vagcom so I can't tell if there are any fault codes but the CEL has remained off.

3. All I did was cut out the OEM cats and replace them with piping of the same size , this allowed me to leave the lambda's in the OEM bungs.

Hoping to find out some good info from tech fundis , otherwise maybe I just need some schrick cams and get a solid REVO 2 tune to really make use of my decat :)

#3
The0ne

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Mine is decatted.

Give it some more miles and your CEL WILL come on.

The rear lamdas will start reading that the emisisons are high so the ecu will bring on the CEL as it thinks your cats are fucked. You can either get a stage 2 remap which will stop the light coming on, you can keep resetting it yourself if you have vag com or you can do what i do and just ignore it ;)
Silver MKV R32 | Milltek Non Res | Apex Springs | Lots of Gloss Black

#4
Lucifer

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No point removing the CAT unless you fit a turbo or super charger.
585 flywheel bhp HPA blackjack turbo conversion. Forged engine,ported head,+1mm Ferrea valves + spring,Schrick 268/264 cams,DRP gearbox with forge gear kit,Clutchmaster FX850,Quaife up front and Peloquin in the rear,Vibratechnic engine mounts + dogbone, roll cage etc.
MK4/5 down pipes, de-cats,sport cats plus full exhaust systems always for sale.

#5
Dazm

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My FI MK5 is de-catted, runs much better without cats(had Miltek cats previously).......you will need to get them coded out of the ECU though.

#6
sixteen10

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The0ne said:

Mine is decatted.

Give it some more miles and your CEL WILL come on.

The rear lamdas will start reading that the emisisons are high so the ecu will bring on the CEL as it thinks your cats are fucked. You can either get a stage 2 remap which will stop the light coming on, you can keep resetting it yourself if you have vag com or you can do what i do and just ignore it ;)

Lol I have been offered a sponsored map from my local REVO dealer so the stage 2 tune is no problem for me. How long did it take for your CEL to come on?

I have driven out 2 tanks of fuel since doing the decat and *touch wood* nothing has come on yet. so around 650-700km thus far.

It does feel like it's much smoother without the cats , but I am very interested in the Milltek headers now so I need to check what that setup will nail me lol :)

#7
Macdaddy©

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Its worth it only if you're going down the FI route IMHO

Is it not horrendously loud now?

It may sound great, But the car will now adjust its fuelling incorrectly and run rich (worse mpg).  Your light will without doubt come one so your better off getting it mapped to also take in account the extra air flow.

De-Cat, Gruppe M and a stage 2 map should give you reasonable gain for n/a unless of course your still using the stock exhaust which is more restrictive than say Milltek in which case it would be a little less.

Go the whole way and fit an aftermarket exhaust too !  I wouldnt expect to see more than 14-16bhp realistically with all your mods though even after stg2 map.  Not sure what that is in KW sorry as i only do the old money lol.

I always found its a lot of money for very little gain although it did give better mid range pull.  

Think with all those mods my Mk4 shaved 0.5 sec of a 0-60 time !
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#8
sixteen10

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Macdaddy said:

Its worth it only if you're going down the FI route IMHO

Is it not horrendously loud now?

Not at all , perfect balance with the Milltek Resonated system and the decat. Great tone at WOT and low noise levels at part throttle. There is no boominess or droning to the system so freeway driving is a pleasure. There are some video's of the sound in my thread :

http://www.r32oc.com...html#post356814

Macdaddy said:

It may sound great, But the car will now adjust its fuelling incorrectly and run rich (worse mpg).  Your light will without doubt come one so your better off getting it mapped to also take in account the extra air flow.

De-Cat, Gruppe M and a stage 2 map should give you reasonable gain for n/a unless of course your still using the stock exhaust which is more restrictive than say Milltek in which case it would be a little less.

Great then I'll have the Stage 2 tune loaded to my ECU but in all honesty the fuel consumption hasn't changed as of yet, I've been hammering it with the new sound and I'm still getting the same consumption as before. :) The tune is wortwhile and I want to get it asap but I was hoping to do the DSG tune at the same time. :(

Macdaddy said:

Go the whole way and fit an aftermarket exhaust too !  I wouldnt expect to see more than 14-16bhp realistically with all your mods though even after stg2 map.  Not sure what that is in KW sorry as i only do the old money lol.

I always found its a lot of money for very little gain although it did give better mid range pull.  

Think with all those mods my Mk4 shaved 0.5 sec of a 0-60 time !

I have the Milltek Resonated system currently , unfortunately I never dyno'd before fitment of the GruppeM but with the Milltek Exhaust and Decat I saw 4whp and 8Nm at all 4 wheels on the OEM software. The torque graph has improved over the entire rev range though and thats what you feel most on the road. I'm not much of a dyno princess , I use it as a tool to measure what impact each mod has had , although thats partly difficult with the Haldex system. If I net another 5-10whp and another 10+-Nm with the stage 2 tune then I'm all smiles :)


On a completely different note are there any documented cons to doing the de-cat on an N/A mk5 R32?

#9
sixteen10

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Just a small thread update.

The car is constantly feeling stronger , she is more responsive than ever.

The CEL has still not come on after nearly 3 weeks , I'm quite impressed. Either way she is getting serviced next week and then loaded with a REVO 2 tune.

Fuel consumption has also gotten slightly better , the trip meter indicates a litre less per 100km than before the decat.

:)




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