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Author Topic: decat help  (Read 5824 times)

Offline alex160

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decat help
« on: 29 July 2012, 21:27 »
Hi all, am looking to decat my 130 gt tdi soon as the stock cat is blowing badly and is making the car a tad sluggish on pick up. On my previous golf which was a 115 gt tdi. I fitted a milltek large  bore down pipe along with a custom 2.5 inch exhaust system. However another company have told me that anything under the 250bhp mark deosnt need a 2.5 system and that it will actually loose you power and that I should stick with standard 2.25 inch system. Basically should I get a milltek large bore decat or a standard diameter decat, I will be getting a custom system fitted in a few months too as the backbox is about to drop off so advice on the rest of the exhaust system would be great too. Thanks
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2001 Golf GT TDi  150bhp/ 250 ftIb torque  *No smoke, No poke*
Jamex coilovers, 8k HID's, 18" RS6 alloys, Pipercross panel filter. Stage 1 Revo remap.THS FR3 engine mounts, Anniversary headlamps. GTI rear spoiler, Miltek largebore decat/downpipe, Pro-speed cat back exhaust system (V6 4mo style tailpipes) *SOLD*

2002 Golf GT TDi 130. Allard egr removal kit, 18" Audi rs6 alloy wheels. Mk5 rear aero wiper.gen R32 roof spoiler, JOM coilovers, JOM heavy duty adj droplinks

Offline Hoggy

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Re: decat help
« Reply #1 on: 29 July 2012, 21:46 »
I've got a THS Decat on my 150 bhp ARL, didn't lose any power and smoothed the pick up out too.
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Offline scarr89

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Re: decat help
« Reply #2 on: 29 July 2012, 22:58 »
Either or mate, you won't lose power at all. I can't see how you would lose power  :undecided:

I have a cat that had been cut off, hollowed out and then welded back together. You could probs just cut out the cat and replace with a piece of pipe. Makes a notable difference :smiley:
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Offline Hoggy

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Re: decat help
« Reply #3 on: 30 July 2012, 18:45 »
Its possible to lose power due to lack of back pressure, but thats doubtful at 130- bhp.
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Offline scarr89

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Re: decat help
« Reply #4 on: 31 July 2012, 14:31 »
Quote from: Hoggy on 30 July 2012, 18:45
Its possible to lose power due to lack of back pressure, but thats doubtful at 130- bhp.

I thought 'back pressure' was a myth?

Read a really good article on how it just doesn't make sense...Why would you want to cause back pressure?

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Offline Agreeable Slick

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Re: decat help
« Reply #5 on: 31 July 2012, 16:15 »
I would like to see who wrote the article as back pressure is certainly not a "myth".

Assuming that a factory system is set up correctly then back pressure can set up waves in the exhaust system, which interact with each other. They can as such aid scavenging of cylinders, and reduce pressure by the exhaust port for next exhaust stroke to allow a faster exit of exhaust gas.

VVT is set up with a view of allowing a exhaust back pressure wave to propagate back in to the inlet system as the inlet and exhaust valves cross over on their opening and closing, that makes the pressure on the inlet increase above nominal and forces more charge in to the cylinder in a RAM air type of effect.

Of course, all of this is relative to the type of engine and power it is creating.
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