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Author Subject: 2.25 system on super high boost?
buzzbrightyear

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Post #1
Hi, powerflow are going to fit a bigger backbox on my car with a 2.25 bore size.
The rest of my system is 2.5 inch.
Would this have any negative effect and will it restrict it as I'm aiming to run around 500bhp with the setup?
its leaking up front somewhere so its going in to be repaired and I thought they may aswell fit the bigger box while it's there as it is pretty damn loud, but they can only get this size box in 2.25 inch.
I wonder how big this box will be as if it's too big it won't fit as the swirl pot will be too close to the heat and exhaust shield will be in the way

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andrew315rawson@live.co.uk
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Posted 31st Jan 2012 at 15:54
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rich_w

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Post #2
2.25” is far too small mate, that’s only really suitable for low-boost.

You want to be at 2.5” or 2.75”.

Mine is 2.5” and 440 BHP – the exhaust gas velocity is very high at the top end, it could probably take another 5% or so, but you definitely don’t want any smaller.

If you restrict it, you will just reduce the efficiency of the whole conversion, which results in more heat, less power and reduced longevity.

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Posted 31st Jan 2012 at 16:14
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buzzbrightyear

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Post #3
Ok mate, advice taken on board I won't be getting it fitted then.
If there's no bigger box available I'll just have to keep the jet noise!
Thanks

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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 31st Jan 2012 at 16:26
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welshpug!

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Post #4
get them to make a silencer if they haven't a big enough one off the shelf.

sideways box like a 206 gti 180 or a 306 touring car should help get the noise down.

have a look at spiky's track car as his exhaust is exactly like this.

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Posted 31st Jan 2012 at 16:51
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phillipm

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Post #5
I'd be running at least a 3" system (or a twin 2.25" system), for the amount of power you're running, it'll probably still cost you a little on the top end but a single 2.25 will strangle it, as rich says, it'll drive the EGT's up too which isn't good!
Even the 2.5" is probably robbing a chunk - for the racers a 2.5 would go out of the window around the 270-280 area.

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Posted 31st Jan 2012 at 17:01
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adam b

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Post #6
Volvos tend to be 3" through cat to 2.5" or 2x2" for anything above 300BHp.
The turbo helps keep the noise down though Wink

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Posted 31st Jan 2012 at 19:14
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buzzbrightyear

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Post #7
Really?
Would this have anything to do with it keeps blowing at the Downpipe-manifold gasket?
The engine is solid it doesn't budge and I used a genuine pug one last time, well I'm guessing it's from there as the system is new.

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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 31st Jan 2012 at 19:38
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buzzbrightyear

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Post #8
Would a 3 inch system be louder

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andrew315rawson@live.co.uk
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My Project thread: http://www.306gti6.com/forum/showthread.php?id=119992&page=1
Posted 31st Jan 2012 at 19:39
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atterz

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Post #9
The sideways box idea is probably your best bet!

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owain wrote:
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Posted 31st Jan 2012 at 21:39
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rich_w

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Post #10
2.5" or 2.75" will be fine.

This application is different to both N/A and turbo cars.

Turbo cars always have larger exhausts as the turbo provides back pressure and noise attenuation, and reducing back-pressure post-turbo helps spool and reduce lag.

You don't want it too big otherwise it will be noisey as hell, with straight through perforated tube silencers you can practically look up the tail pipe and see the exhuast valves, which is why it's loud. The more power, the more noise is the way it goes.

Also make it too large means you compromise the low and middle range power / torque, you would also want to run less overlap on the campshaft timing, if it's too free flowing you tend to over-purge the cylinders with the pressurized inlet charge meaning some of it goes to waste out the exhaust.

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Posted 31st Jan 2012 at 22:26
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atterz

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Post #11
Bloody hell, supercharger tuning really is an art. Not to big, yet not too small... im so used to turbo exhausts, bigger is normally better.

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owain wrote:
A GTI-6 with a good dashboard and the seats down can outsprint an E46 M3 in July.
Posted 31st Jan 2012 at 22:41
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binkagti

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Post #12
I know stan when we go to south of france i think is 4 inch straight through, it sounds like the world is coming to an end, especially funny starting the car on the eurostar, the 10 cars behind him were deaf lol.

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Posted 31st Jan 2012 at 22:43
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atterz

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Post #13
Haha Smile Didnt hear Stans at FCS last year, is it really that loud?

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owain wrote:
A GTI-6 with a good dashboard and the seats down can outsprint an E46 M3 in July.
Posted 31st Jan 2012 at 22:47
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rich_w

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Post #14
binkagti wrote:
I know stan when we go to south of france i think is 4 inch straight through, it sounds like the world is coming to an end, especially funny starting the car on the eurostar, the 10 cars behind him were deaf lol.



Stan's is a 2.5" magnex, the only thing thats 4" is the tail pipe on the back box Smile

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Posted 31st Jan 2012 at 22:52
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rich_w

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Post #15
binkagti wrote:
I know stan when we go to south of france i think is 4 inch straight through, it sounds like the world is coming to an end, especially funny starting the car on the eurostar, the 10 cars behind him were deaf lol.



Stan's is a 2.5" magnex, the only thing thats 4" is the tail pipe on the back box Smile

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Posted 31st Jan 2012 at 22:52
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stan_306gti6 Forum Admin

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Post #16
Yes, that's right it's 2.5" all the way through with the tailpipe at 4".

atterz - You wouldn't have heard it at FCS last year because I have to change the exhaust and put the centre silencer back in to bring it down to 98dB to pass the noise level test.

In it's current form it is 131dB, which is the straight through centre section exhaust I use for road use. This is why it is incredibly loud when we go to France as Binka can confirm. Thumbs up

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Posted 1st Feb 2012 at 07:11
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buzzbrightyear

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Post #17
I'm surprised it's only 98db with the magnex

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andrew315rawson@live.co.uk
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My Project thread: http://www.306gti6.com/forum/showthread.php?id=119992&page=1
Posted 1st Feb 2012 at 07:57
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stan_306gti6 Forum Admin

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Post #18
buzzbrightyear wrote:
I'm surprised it's only 98db with the magnex


Deffo is, as I have had it tested. I just wish they would let me go on track with the straight through as it doesn't develop as much power with the centre box in!

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Posted 1st Feb 2012 at 09:34
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buzzbrightyear

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Post #19
Is it a Noticable difference?

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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 1st Feb 2012 at 10:38
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stan_306gti6 Forum Admin

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Post #20
buzzbrightyear wrote:
Is it a Noticable difference?


It is in the higher RPMs mate, you can really notice it then.

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Peugeot 306 GTi-6
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Posted 1st Feb 2012 at 12:43
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birk

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Post #21
There will be no telling bret though dude.

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Posted 1st Feb 2012 at 13:01
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buzzbrightyear

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Post #22
birk wrote:
There will be no telling bret though dude.

LOL

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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 1st Feb 2012 at 14:35
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atterz

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Post #23
Is it not possible to get a really large center silencer that deadens the noise whilst maintaining high end flow? To be fair supercharger owners are shit out because as mentioned before turbos act as a natural silencer and the majority of big power cars are turbo.

But there must be somthing.

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owain wrote:
A GTI-6 with a good dashboard and the seats down can outsprint an E46 M3 in July.
Posted 1st Feb 2012 at 14:38
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