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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 05-23-2007, 10:23 AM   #1
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Default cheap bosch bov replacement

I needed to replace my leaking bosch and went for a cheap (<$30) ebay unit. It's a direct swap for the bosch, comes with two springs and is adjustable. It was recommended to me by an XR4ti owner that's running 20+ psi with it. I'm using the weakest spring with some reduced tension on the adjuster and it's holding ~15psi without leaking. All machining looks great- took it apart and the tolerances appear to be good and tight. It uses O-rings as seals for easy maintenance. It's been on for almost a month and still works well and sounds great VTA- no louder than the bosch- still stealthy.

ebay bosch replacement

they've also got a purpose-built VTA too
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Old 05-23-2007, 10:57 AM   #2
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Purple. Gross.
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Old 05-23-2007, 11:19 AM   #3
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Nice, I have a friend with a turbo maxima local that has been having massive issues upping his boost... we all suspect the Bosch bovs... I'm going to forward this to him.
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Old 05-23-2007, 11:22 AM   #4
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Yes purple is gross. Cheap is good. Plus mine sits under the cold side IC pipe by the TB, so it's well hidden.

My guess is the bosch unit leaks far before it's obvious.
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Old 05-23-2007, 11:29 AM   #5
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He also sells a VTA version of the BOV, and a greddy knock-off too.
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Old 05-23-2007, 10:04 PM   #6
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I had a forge blow-off valve that VTA, so i had stumbling and stalling problems.....installed new bosch recirculated car runs perfect... if the bosch is recirculating what does it matter if its leaking at idle?
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Old 05-23-2007, 10:50 PM   #7
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if it's leaking you're losing boost and making your turbo work harder to maintain boost if it can even keep up. you can overspin the turbo and damage it this way, not to metion push much hotter air
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Old 05-23-2007, 11:44 PM   #8
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at what psi do they start to leak
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Old 05-24-2007, 12:32 AM   #9
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At 15psi mine stayed open- and if boost "tried" to go up, the bosch bov made what sounded like a continuous whooooooooooosh - w/o "sh" on the end. I swapped in this new unit and was running 17psi+ peak up from 15 previously with the bosch- no change to the mbc.
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Old 05-24-2007, 12:36 AM   #10
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but keep in mind 15 psi from Rob's t3/t4 is pushing a lot more air than 15 psi from what most of us are running. a greddy kit should get away with using the plastic bosch bov at upwards of 15 psi. probably a 2554 or maybe even a 2560 could too.
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Old 05-24-2007, 01:31 AM   #11
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Thanks for the link.
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Old 05-24-2007, 02:25 AM   #12
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Quote:
Originally Posted by Ben View Post
but keep in mind 15 psi from Rob's t3/t4 is pushing a lot more air than 15 psi from what most of us are running. a greddy kit should get away with using the plastic bosch bov at upwards of 15 psi. probably a 2554 or maybe even a 2560 could too.
Ok i dont fully understand what you are saying. wouldn't 15psi of air in the piping be 15 pounds of pressure pushing against the piping regardless of the pump pushing it? The bigger turbo just has to spin less fast to keep up and thereby creating less heat, ammounting to greater air density and therefore more power. Air temperature doesnt affect how my boost pressure gauge reads, why should it affect the way a pressure operated valve (read BOV) operates?
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Old 05-24-2007, 09:49 AM   #13
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Yeah Ben- this is beyond my comprehension. I'd think the only thing that matters to the BOV is pressure. After pushing on the bosch unit with my finger, I'm amazed it held pressure as well as it did.
Brgracer had the same problem with his greddy at 15psi.
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Old 05-24-2007, 11:16 AM   #14
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Do you guys think the bosch will hold 12 psi on a td04hl-15g.
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Old 05-24-2007, 11:23 AM   #15
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My Bosch BOV makes a farting honking noise. I think I'd rather have one of these purple deals in the car. Thanks for the heads up Rob.
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Old 05-24-2007, 11:39 AM   #16
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don't confuse pressure with quantity. corky bell sometimes writes "not all boosts are created equal." 15 psi from your "big" turbo is flowing a lot more air than 15 psi from my td04. How much more, well I hate compressor charts, but probably 75-100 hp more air.

the 90 I bought, which was capable of 15 psi, didn't seem to have a leaky BOV problem. it had your standard bosch plastic bov. for grins and giggles, i could try it in my 91.
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Old 05-24-2007, 11:49 AM   #17
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I get it now - flow and pressure as two different things.
this bov really sounds good vta just loud enough
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Old 05-24-2007, 01:22 PM   #18
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Pressure will be a measurement of resistance against a bottleneck. Given the same bottleneck (in this case the engine) and pressure the same amount of air is being moved regardless of what turbo is being used. Any difference in power will be a result of compressor efficiency.

Flow ratings will be volume against time.

In other words, 15psi is 15 psi.
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Old 05-24-2007, 01:38 PM   #19
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From a basic fluid mechanics standpoint, if two pressures are the same, the volume of air does not necessarily have to be the same. It depends on temperature which, as suggested, is related to compressor efficiency. But frankly, we don't really care much about pressure, volume, or temperature by themselves. Only the combination of the three in calculation of the actual amount (# molecules) of O2 will tell us exactly how much "air" we are putting into the engine.

Volumetric flow rate only tells part of the story.
Pressure only tells part of the story.
Air temp only tells part of the story.
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Old 05-24-2007, 01:42 PM   #20
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Quote:
Originally Posted by PAT! View Post
Pressure will be a measurement of resistance against a bottleneck. Given the same bottleneck (in this case the engine) and pressure the same amount of air is being moved regardless of what turbo is being used. Any difference in power will be a result of compressor efficiency.

Flow ratings will be volume against time.

In other words, 15psi is 15 psi.
I disagree. The "amount of air" being forced into the bov via the turbo is going to be dependant on the turbo. The turbo would be the bottleneck in the example.
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