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Author Subject: Obscene volume?
greenie

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Location: Sandhurst

Registered: 06 Feb 2013

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Post #1
So a while back I bought an exhaust from someone who will remain nameless that was apparently off an otherwise standard gti6.
It is a magnex back box with 2.5 inch straight through to where the cat section would normally join it.
When I took delivery it was obvious that the connection to the cat section was not standard. I subsequently bought a 2.5 inch decat all stainless to have welded on.
This gives me straight through from the manifold to a single silencer at the back.
If I go ahead with this will it be stupidly loud and draw attention to the fact I gave a decat on?
Is any one interested in buying this for the track so I can buy something more sensible for the road?
Posted 19th Jun 2014 at 12:54
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greenie

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Post #2
Thinking out loud,
If I had a 200 cell sports cat welded in would I get away with the noise anyway as it should be 'mot'able?
Posted 19th Jun 2014 at 13:26
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cjm_harris

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Registered: 04 Dec 2007

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Post #3
Well, from what I have heard decatted Magnex with a centre box in are silly loud and boomy. I would say that removing the centre box would make it even louder.

You will also have issues with scavenging exhaust gases from the head, as with the larger diameter pipe and no boxes, there will be very little back pressure. This means you will loose some low down grunt, but it may be a bit more free revving further up the rev range.

One final point to make, the exhaust you have will be useless for track. Most tracks have a 95 or 98 Db limit, and this exhaust would definitely be over 100 Db.

HTH

________________________________________

Chris
1999 China Gti6 Supercharged Devil [Fun car] >>Project Thread<<
2000 Bianca 306 Diesel [Work runabout]
Posted 19th Jun 2014 at 14:59
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greenie

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Location: Sandhurst

Registered: 06 Feb 2013

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Post #4
Great info, thanks for taking the time.
Looks like I will scrap what I have and start again then.
Actually, can I buy a magnex mid box to suit?
Posted 19th Jun 2014 at 19:17
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cjm_harris

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Post #5
Yes, you will be able to buy a Magnex mid section, or any custom exhaust place will be able to sort you out Smile

________________________________________

Chris
1999 China Gti6 Supercharged Devil [Fun car] >>Project Thread<<
2000 Bianca 306 Diesel [Work runabout]
Posted 20th Jun 2014 at 13:08
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bennn

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Location: Shrewsbury

Registered: 05 Sep 2008

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Post #6
I had a 2.5" magnex with decat. I had a custom centre section welded in and it wasn't too bad.

It'll be f*cking loud without a centre silencer with or without a cat as the cat doesn't do much in the way of silencing.

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Cherry Red 306 HDI
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Posted 20th Jun 2014 at 14:00
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ryangti6

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Location: Pontypool

Registered: 01 Sep 2006

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Post #7
I had a magnex cat back on my old '6 and thought that was a nice noise, took it to long life to decat and due to the centre silencer being split got them to take that out too and it was stupidly loud and very raspy too. When the mot came around and I refitted the cat it sounded a lot better so I ended up leaving mine like that.

Either no cat or no midbox I'd say is fine going from others I've owned/seen but I wouldn't have both removed again.

________________________________________

Ryan
Posted 20th Jun 2014 at 15:15
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greenie

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Post #8
Nice info guys. Thanks
I need to get the thing welded up so will probably get a 200 cell cat put in first so at least it's legal. Then if it's too loud pop in a universal silencer in the middle.
In your opinions would having both the cat and two silencers help with the back pressure issue?
I have a ported manifold and k and n filter to help with the intake.
Posted 20th Jun 2014 at 21:48
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stan_306gti6 Forum Admin

Location: Kent

Registered: 18 Jan 2004

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Post #9
I have a Devil Decat, with a straight through centre section and 4" Magnex back box. Yes

It's 132dB at static noise test and at full chat you can hear it over one mile away. Laugh

I also have a centre section with a box in it which I used to swap over for track work which dropped the level to 105dB. To be honest, the track setup was stupidly loud, the road setup was louder than a jumbo jet...however I liked it, so that's how it stayed.

I can agree about the back pressure though, with no centre box you do lose a lot down low with no CAT either, however it wasn't too bad on mine due to the charger. I'd imagine on NA you'd be waiting forever and a day for it to pick up from low down. I did it mainly for freer revving at the top.

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2000 (X), Moonstone Love
Posted 20th Jun 2014 at 22:47
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russbez

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Post #10
ah goodness me

im planning removing my magnex centre section, maybe not my best idea?

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Posted 21st Jun 2014 at 00:21
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stan_306gti6 Forum Admin

Location: Kent

Registered: 18 Jan 2004

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Post #11
russbez wrote:
ah goodness me

im planning removing my magnex centre section, maybe not my best idea?


Unless you're a fan of ridiculously loud like me, then probably not. LOL

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"Supercharged - 454.1bhp/317.5lb/ft"
Peugeot 306 GTi-6
2000 (X), Moonstone Love
Posted 21st Jun 2014 at 08:35
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jimmyhackers

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Location: birmingham

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Post #12
was it me?

im sure i sold a decat pipe that had be previoulsy crafterd by some other pleb off of ebay. i didnt even fit it and got tip top to make me one from scratch for 150 quids.

then a lorry destroyed that car about 3 days later Sad

decat = bad things all round

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the world is changed by people in sheds
Posted 25th Jun 2014 at 00:17
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buzzbrightyear

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Post #13
DOES THIS SOUND OBSCENELY LOUD??

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andrew315rawson@live.co.uk
Moonstone phase 7 gti6
My Project thread: http://www.306gti6.com/forum/showthread.php?id=119992&page=1
Posted 25th Jun 2014 at 01:04
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buzzbrightyear

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Post #14
jimmyhackers wrote:
was it me?

im sure i sold a decat pipe that had be previoulsy crafterd by some other pleb off of ebay. i didnt even fit it and got tip top to make me one from scratch for 150 quids.

then my engine fell out the car and landed 350 yards away about 3 days later Sad

decat = bad things all round

________________________________________

andrew315rawson@live.co.uk
Moonstone phase 7 gti6
My Project thread: http://www.306gti6.com/forum/showthread.php?id=119992&page=1
Posted 25th Jun 2014 at 01:05
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RetroPug

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Registered: 15 Jan 2013

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Post #15
stan_306gti6 wrote:
I have a Devil Decat, with a straight through centre section and 4" Magnex back box. Yes

It's 132dB at static noise test and at full chat you can hear it over one mile away. Laugh


Why do you hate your ears?


Oh wait, you never get to hear it... LOL

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61k miles Ph.1 Diablo '6 Project Thread
Posted 25th Jun 2014 at 09:12
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welshpug!

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Location: Bigend, Wales.

Registered: 27 Mar 2007

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Post #16
I'd rather hear something like colin and sandys creations, pure induction.

I.e you only make noise with your toe in, so youre not seen as an antisocial c**t

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Posted 25th Jun 2014 at 09:29
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buzzbrightyear

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Post #17
IS THIS ANTISOCIAL?

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andrew315rawson@live.co.uk
Moonstone phase 7 gti6
My Project thread: http://www.306gti6.com/forum/showthread.php?id=119992&page=1
Posted 25th Jun 2014 at 09:56
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russbez

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Location: Inverness-Shire

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Post #18
it is Thumbs up

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My Rallye project thread
Posted 25th Jun 2014 at 10:32
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jimmyhackers

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Registered: 14 Jun 2011

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Post #19
indeed......decat is seen as antisocial by every other road user.

its why said police officer took it upon himself to hate me for crashing, regardless of the fact he didnt even see the crash.

just me overtakeing him (legally) was enough for him to make it his mission to end my driving career

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the world is changed by people in sheds
Posted 25th Jun 2014 at 17:40
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anth

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Location: Colchester

Registered: 04 Apr 2006

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Post #20
I had a straight through into a Powerflow back-box which frankly was not much bigger than a bike racing can.

It was running with a Cat at one point and that was boom'ier, removing the cat made it less droney but it was rather loud.

I'd go with Welsh Pugs recommendation if such a thing exists. I got rid of mine for a Jetex which was still quite loud after a time.
Posted 25th Jun 2014 at 18:37
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