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Old 05-17-2002, 07:09 AM   #1
WRXterminate
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Question Downpipe - twin dump vs single

Is there any dyno evidence whether a BPM style pipe (twin dump)
that separates the wastegate exhaust over a long stretch of the pipe is significantly better than something with a single, albeit large mouthed, pipe like the TurboXS downpipe? (And you all know Vishnu is developing a twin dump with a cat and is claiming good performance numbers.)

http://www.subaruwrxparts.com/parts/bpm_dp_2.jpg

http://www.turboxs.com/WRX%20Exhaust.htm
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Old 05-17-2002, 07:40 AM   #2
Dori Dori
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If you do a search, there is a very good thread out there...I forgot who started it though...

Basically, most people feel that on the stock turbo, it doesn't really make a difference. Shiv and Joel at Vishnu feel different though.

Everyone does agree though, that in design, the twin dump is better.
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Old 05-17-2002, 08:19 AM   #3
WRXterminate
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Actually I did do a search, but it didn't turn up any dyno plots, scientific evidence.
Someone did say though the TXS pipe gave smoother power than the BPM twin dump, which should show up on a dyno.

Note: I'm considering the MRT downpipe which is somewhere in between the two types to cover my bets (and reduce the possibility of a CEL). Vishnu is my other option, but it isn't available yet.
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Old 05-17-2002, 08:40 AM   #4
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id think that godspeed would be a good option if you are worried about cel's
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Old 05-17-2002, 03:04 PM   #5
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And which one should I choose If I go with a VF30? Would love to add the Vishnu with an HKS or Kakimoto, though I guess it will not work with neither of these.
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Old 05-18-2002, 01:40 PM   #6
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For a Vf30, it honestly won't matter if you go twin dump or bellmouth...just make sure the wastegate gasses are not totally blocked off (like the factory downpipe).

Twin dump is a nicer design, more costly to make, and tends to fit better though.....it also will take you further should you upgrade from the VF30 in the future.....

adam
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Old 05-20-2002, 08:54 AM   #7
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Cool

Thanks, Z1
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Old 05-20-2002, 11:12 AM   #8
amelnikov
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A twin dump or a bell mouth is there for boost control, not horsepower. When in boost your wantegate for the most time is closed and nothing is going though there. Only when you have a turbo that gives you boost creep, only then will having a smooth or even a sepate path for the wastegate give you more power and better wastegage control. Speaking from experience.

Alex...
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Old 05-20-2002, 11:20 AM   #9
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With the STI OE turbo (VF23 I think?) I have tried both a twin dump and single dump design, In terms of power, they are not far off. You might say no diff but the sound, Oh my God the sound!!! With the twin dump, the sound it makes when the wastegate starts dumping boost is incredible. It like having another blow off valve going off during full throttle.
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Old 05-20-2002, 11:22 AM   #10
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Listen, do a search, I've discussed this many times before. Simply put twin-dump is better for preventing the wastegate charge from disrupting the airflow coming out of the turbo. Now this really isn't a factor until you reach 400+ horsepower. So until you reach that power level, which most people aren't, then the extra expense of running a twin-dump system isn't really worthwhile. For most street driven applications, a properly designed bellmouth like Cobb's Cast unit on their down-pipe should be more then adequate.

sherif
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Old 05-20-2002, 11:25 AM   #11
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Quote:
Originally posted by Dori Dori
Basically, most people feel that on the stock turbo, it doesn't really make a difference. Shiv and Joel at Vishnu feel different though.

Everyone does agree though, that in design, the twin dump is better.
One possible rational for Shiv and Joel at Vishnu feeling this way is because their stage packages are progressive. Each stage builds upon itself, so by the time they drop stage 3 and 4, the car would be making monster power, so a twin-dump setup becomes more efficient.

sherif
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Old 05-20-2002, 12:05 PM   #12
Conduit
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I know you have "discussed this many times before" but the purpose of the twin dump isn't to prevent the wastegate exhaust from interfering with the turbine section exhaust, it's the other way around. You probably know that and just got it backwards
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