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How leaky is the OEM diverter valve?


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I've seen posts of which DV or BOV folks are using, but nothing that really offers some substance to the ability of the OEM valve to hold boost. Poking around elsewhere I've seen thing suggesting as low as 3 psi and leaking starts, to 10-12psi before leakage to the OEM valve is fine.

 

As I understand it, a leaky valve means a higher waste gate duty cycle, so less efficiency (and I imagine more heat) and the turbo, and maybe reduced boost response, but isn't going to change peak boost, etc. as that's defined in the map you are using.

 

I've been looking at the Turbosmart Kompact 34mm plumb back valve, as it seems very well priced and has a decent track record from what I have read. I'm still trying to convince myself it's needed, though.

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Somebody on the forum tested the OEM BPV on video and put it on YouTube. It would likely provide the substance you are looking for. Unfortunately, I couldn’t find it. Maybe somebody else will halve better google-fu than me.

 

That being said, I think your logic is spot on. I rationalized that I simply didn’t like the idea that I have a leak....

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Someone here took the time to actually measure the leakage of the OEM valve and posted results here. It's probably somewhere in the archives now.

 

I never really checked mine at stock levels as the car runs fine and IIRC it starts leaking beyond stock levels. I will be replacing it when I start modding though.

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There is no easy answer as to how much or if it leaks, because it will perform differently on the vehicle rather than on a bench. The easiest way I could think to "test" it would be do back to back datalogs changing only the valve out. But there is also some variability there.
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I dunno - it's definitely a leak, but given the flow rate through the intake under boost, it seems pretty negligible... figure the engines using in the neighborhood of 500-600+ cfm at 5000rpm or so - that sounds like a couple of cfm leak - you can definitely hear it, but it's likely way under 1% of the total flow... Would be interesting to see an aftermarket diverter valve under similar conditions - I'd be surprised if they all don't leak a little...

 

I guess more important than a leak is how well the diverter valve does it's job to prevent compressor surge. The OEM plastic design just looks like it should be sticky/slow in that respect, which maybe is a bigger reason to go aftermarket...

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So, this is anecdotal obviously. . . I was stage II, replaced the OEM BPV with the Turbosmart BPV, and over boosted the first time a stomped on it. Had to get a new tune. This leads me to believe that the OEM leaked a significant amount.
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What boost pressure were you running, and how much was the overboost? (was target 17 and you hit 18, or more like 20?) Was this an OTS map, or a protune? (I am guessing the latter, as they might have tuned for the BOV behavior) - at least for the Cobb OTS maps, the target peak boost is only 0.5-1psi higher for their stage 2 map over their stage 1 map.
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I wonder if the diaphram was torn or something in the OEM one... I am not sure why a BOV/DV would cause an overboost condition unless maybe it didn't open properly? The car should be using the wastegate to control the boost pressure based on the pressure in the manifold, and the BOV should be closed... I don't know enough about how the WGDC, etc. is incorporated into a tune, but there must have been something...

 

How bad was the overboost? (and this wasn't a spike?)

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FWIW I didn't notice any difference changing from the stock charge pipe and bpv to the racerx charge pipe and turbosmart bpv, or when i changed them back. I was on an OTS tune at the time and getting a protune when I went back to stock.

 

Fast forward slightly and I replaced the OEM bpv again with a 34mm Turbosmart valve in the stock location, again no noticeable difference in any of my gauge on the AP.

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When I added my Turbosmart Kompact BPV, my car peak boost went from 17psi to 18psi on Cobb OTS 93octane 17psi tune. It was the only mod I did at the time (I did it with my timing belt/water pump). It seem from my 'butt dyno' that the car was responsive and built boost faster.
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I held off on installing my BPV for a while because I was having a hard time getting my DAM to go up to 1.000 (resets to .812 on key-off) and I wanted to figure out if I had another issue first. Went from stock to RacerX charge pipe and Synapse DV, DAM was more than happy to go right up to 1.000 under the same conditions.
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FWIW I didn't notice any difference changing from the stock charge pipe and bpv to the racerx charge pipe and turbosmart bpv, or when i changed them back. I was on an OTS tune at the time and getting a protune when I went back to stock.

 

Fast forward slightly and I replaced the OEM bpv again with a 34mm Turbosmart valve in the stock location, again no noticeable difference in any of my gauge on the AP.

That makes me wonder where the leak is coming from on the leaking OEM diverter valves, and making me think that it's a failure mode and not an intrinsic property (i.e., they don't all leak until some sort of internal failure) - if it's getting by the seal, or if it's from the control side, getting through a hole in the diaphragm... Poking around about the Bosch diverter valves, it looks like there were issues with some Audi engines with the diaphragm tearing, leading to an overboost code... possibly another reason to go with a piston based system - no diaphragm to rip/tear and leak?

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  • 6 months later...
When I added my Turbosmart Kompact BPV, my car peak boost went from 17psi to 18psi on Cobb OTS 93octane 17psi tune. It was the only mod I did at the time (I did it with my timing belt/water pump). It seem from my 'butt dyno' that the car was responsive and built boost faster.

 

Do you mind telling me which Kompact BPV you have? Have a new AP for my 2010 LGT and it seems to be leaking boost. 130k miles on it, so its not that much of a surprise.

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Do you mind telling me which Kompact BPV you have? Have a new AP for my 2010 LGT and it seems to be leaking boost. 130k miles on it, so its not that much of a surprise.

 

From my email receipt, Turbosmart BOV Kompact Plumb Back 34mm TS-0203-1223

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