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Old 06-27-2011, 12:01 PM   #1
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Default Exhaust Manifold backpressure question

So I was playing with the BW turbo configurator and it estimates 9psi backpressure at the turbine (with boost set to 21psi), what would be considered excessive? Obviously 0 would be best but seeing as the TS housing on the 6258 and 6758 wont be happening, this is the best that can be done. With a goal of 400-450 (leaving some play in case I can't keep up at 400), the 6758 is the ideal setup for my goal if this isn't too bad..

Here's a link to the config.

Edit- It also states that the wastegate is 'flow choked', I assume it's because it's of insufficient diameter, thus needing an EWG?
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Old 06-27-2011, 12:13 PM   #2
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How can you have less pressure on the turbine side and more pressure on the compressor side? Without more pressure on the turbine side this sounds like a magical turbo.
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Old 06-27-2011, 12:16 PM   #3
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9psi on the turbine side. Essentially there's pressure built up in the exhaust manifold, throttled by the turbo.
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Old 06-27-2011, 12:28 PM   #4
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Originally Posted by Der_Idiot View Post
9psi on the turbine side. Essentially there's pressure built up in the exhaust manifold, throttled by the turbo.
Anyone I've ever spoken to says there's 1.5-2x more pressure on the turbine side than the compressor side because it takes equal or more energy to turn the compressor. I'm not an engineer, but I'm quite eager to read more on this.
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Old 06-27-2011, 12:36 PM   #5
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Quote:
Originally Posted by hustler View Post
Anyone I've ever spoken to says there's 1.5-2x more pressure on the turbine side than the compressor side because it takes equal or more energy to turn the compressor. I'm not an engineer, but I'm quite eager to read more on this.
Pretty sure that's wrong. Energy =/= pressure
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Old 06-27-2011, 12:45 PM   #6
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Quote:
Originally Posted by hustler View Post
Anyone I've ever spoken to says there's 1.5-2x more pressure on the turbine side than the compressor side because it takes equal or more energy to turn the compressor. I'm not an engineer, but I'm quite eager to read more on this.
thats indeed wrong, and you can buy exhaust pressure sensor to go into the manifold to see if you wanted.

With audi's antilag they were pushing air though the intake into the exhaust manifold once more pressure built up in the intake compared to the exhaust manifold
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Old 06-27-2011, 12:46 PM   #7
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Pretty sure that's wrong. Energy =/= pressure
heat energy causes increases pressure, transforms into kenetic energy.
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Old 06-27-2011, 12:52 PM   #8
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heat energy causes increases pressure, transforms into kenetic energy.
but is there energy lost?
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Old 06-27-2011, 12:52 PM   #9
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Quote:
Originally Posted by hustler View Post
Anyone I've ever spoken to says there's 1.5-2x more pressure on the turbine side than the compressor side because it takes equal or more energy to turn the compressor. I'm not an engineer, but I'm quite eager to read more on this.
This is not true and a huge overgeneralization as well, even if it was true. Exhaust gas pressure in the manifold is a function of many variables and will vary from being more than your intake charge pressure to less than your intake charge pressure, largely a function of engine speed and load.

Quickly looking back at some data I've collected in the past on this stuff, exhaust gas pressure varied from 1.75 to .70 of intake pressure. Lower load and low engine speed generally translated to higher exhaust/intake pressure ratio.
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Old 06-27-2011, 01:12 PM   #10
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This is not true and a huge overgeneralization as well, even if it was true.
Tone down the disrespect.
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Old 06-27-2011, 01:29 PM   #11
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but is there energy lost?

of course. just sayin.
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