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 Post subject: exhaust dumps
PostPosted: Fri Feb 02, 2018 6:10 pm 
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Joined: Tue Feb 28, 2012 4:35 pm
Posts: 833
Location: Hamilton, Canada
has anyone tried exhaust dumps after the header in their Gti?
I was planning on doing a new exhaust but thought this could be an alternative, which would also keep my not too loud exhaust sound while normal driving.
I have heard so many conflicting arguments about back pressure and what not I don't really believe anyone at this point about the subject :lol: but the previous owner of the car said that when he unbolted the this exhaust from the header it was a huge improvement.

thanks

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89 Swift gti
Modified B16 P29 75mm pistons,13:1CR, cultus intake, genie header, genie exhaust, 3tech head, 3tech 222/365 cams, 3tech UD pulley, megasquirt 2.0, 60mm throttle body, Aluminum flywheel


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 Post subject: Re: exhaust dumps
PostPosted: Fri Feb 02, 2018 8:28 pm 
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Joined: Wed Jan 07, 2004 10:52 pm
Posts: 225
Location: Qc Canada
i remember back in the days with genie header and a 2 1/4 straight pipe making noise, when i switched back to stock exaust i noticed a lot more low end torque

i would unplug it and do a dyno run, if too much loss put the cutout in the back, or in the muffler

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swift 2000
megasquirt efi
rx7 460cc injectors
td05h-16g @ 18 psi
SRP forged civic piston
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 Post subject: Re: exhaust dumps
PostPosted: Fri Feb 02, 2018 10:34 pm 
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Joined: Thu Apr 15, 2004 12:27 am
Posts: 3060
Location: Aruba
On my turboed GTi I have an exhaust cutout valve installed (ebay). On the street the exhaust gasses flow through the stock muffler. Reaaally quiet.
At the track, i flip the switch and the valve opens from under the car. Reallly loud and agressive (cams).

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1991-GTi: JE 75mm 11:1 pistons,Ported head, Single UD pulley (OCC),Sandros chip,Aluminium flywheel,3tech 222/365 cams, Cultus headers,Cultus IM,50mm tb,Crane cams adjustable cam gears,Apex suspension, 4.39fd GB.
1989-GTi: 3Tech 210/340 Cams,Cultus IM, B&G springs, TD04L turbo, Apexi SAFC, Suzukird UD pulley, Circuitse7en dual boost controller, AEM wideband, AEM water / meth injection kit, HKS bov.
2001-Altezza AS200: Stock.-sold
2003-EVO7 GT-A
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 Post subject: Re: exhaust dumps
PostPosted: Sat Feb 03, 2018 11:55 am 
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Joined: Fri Sep 21, 2012 9:23 am
Posts: 184
Location: Mount Vernon, WA
I would say that after the header is reduced down to one that that there not going to be a significant change. After going from 4 to 1 and short amount of single pipe that most of the variables have been already calculated. I think the diameter, thickness, length, bend of the header will determine most things. Then next most important would be the design and length of the merge collector from 4 to 1. Including the exit diameter of the merge collector. Once the air has gotten past this point and the diameter of the exit pipe from the collector is set I don't think you will find too much difference in the power band rev changes. Installing a dump pipe at that point will definitely open up the cfm flow high up with minimal effect of everything else.


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 Post subject: Re: exhaust dumps
PostPosted: Sat Feb 03, 2018 12:52 pm 
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Joined: Sun Mar 24, 2002 3:06 am
Posts: 3351
Location: In T-Dot-getting >35mpg in a non GTi
beached wrote:
has anyone tried exhaust dumps after the header in their Gti?
I was planning on doing a new exhaust but thought this could be an alternative, which would also keep my not too loud exhaust sound while normal driving.
I have heard so many conflicting arguments about back pressure and what not I don't really believe anyone at this point about the subject :lol: but the previous owner of the car said that when he unbolted the this exhaust from the header it was a huge improvement.

thanks


a normal 1 7/8" street exhaust and dump available for the track should be fine... but it's not clear what you're really looking to objectively improve...or even subjectively?
are you trying to pare down some tenths somewhere? or looking for the max dyno sheet?

beyond max wot potential benefit, I don't think there's much on the table in most normal circumstances.

Now, this is coming from the guy that drove to cayuga right off the genie header (me) with that car... LOL.... and yes, there are some scraps of paper somewhere that confirm it helped me... but that's when i was chasing tenths...back when people drove manual transmission cars and gasoline powered cars were still the only option. Im pretty sure Sandro did his best runs right off the header too. at WOT, as open and free as you can get is pretty much the best.

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