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$0.16 BOV mod on NASIOC


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I have had a hard time finding any helpful threads on this forum about this mod. I read through most of the pages of this thread on NASIOC:

http://forums.nasioc.com/forums/showthread.php?t=454965

 

I am just curious to see how many of us have tried this w/ success on the stock BPV. My tuner has told me that due to the elevation in SLC stock BPV only holds about 15-16 lbs of boost. Just wanting to hear opinions on this and more people that have had experience with this on an LGT.

 

Thanks!

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So you take advice from a forum dedicated to a different car and more importantly a different engine (2.0) and different parts (BOV) and expect to achieve safe results? Go ahead. The thread you referenced is 10 years old...
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This mod applies to any bpv of recirculating design that has a lower boost reference hole in addition to the boost/vac hose on top. That means it will work on the lgt.

There's even a company that does this in Japan and sells the modified valves at ripoff prices: http://www.coto-sports.com.

 

Anyway, I did this a couple of years ago, both on my oem bpv, and my dsm 1g bpv (metal!) that I modded to fit the lgt flange.

You'll likely see some mild compressor surge on moderate throttle shifts which isn't harmful, but it won't do a damn thing performance wise.

Theoretically your bpv will close faster on boost and keep it shut even at higher boost levels with the mod, but higher boost levels seem to play nice with the lgt bov.

In summary, not worth the time or effort unless you're bored and have nothing to do.

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I did this on my 05 LGT. I had to retune slightly after the AVO380 because it was apparently leaking pre-mod. I credit its modified capacity to my 5EAT LGT's power through the gears

 

I did this on my 11 WRX. Why not, it provides every positive attribute of a Forge, but for virtually free. Plus, it has the reliability of an OEM part. This one was plastic like the LGT's BPV. The addition to the WRX's driving performance was immediately obvious.

 

I did this to my 11 STi. Better, all metal construction, but basically the same BPV. Better, bigger, vent orifice... for the bigger TMIC, I guess. Same process to modify. Same welcomed addition to driving/power performance. Even gave it a twist of my own.

 

Anyone who has read the complete mod thread "over there" will come across my posts. I've been vocal about the virtues of this mod for years on here as well as other forums. It provides virtually the same BPV as was OEM on JDM STi at one time, at FAR less cost than importing one. Lots of years, three different turboed Subarus, all without an issue, all while addressing once and for all every issue related to a BPV/BOV.

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If your BOV is leaking, it's broken or you've got it hooked up wrong.

 

BOV's not being able to hold boost above xx is complete BS. By design, they don't care what the boost pressure is. They always have the same spring pressure holding it closed.

(Updated 8/22/17)

2005 Outback FMT

Running on Electrons

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  • 10 months later...
If your BOV is leaking, it's broken or you've got it hooked up wrong.

 

BOV's not being able to hold boost above xx is complete BS. By design, they don't care what the boost pressure is. They always have the same spring pressure holding it closed.

 

Read the nasioc thread before you come out with one of your usual dumb generalizations :spin:

 

It's obviously false with the stock design BPV. Under boost, the stock has positive manifold pressure applied to all:

 

the bottom of the valve, AND

the bottom of the diaphragm, AND

the top of the diaphragm.

 

Yes, there are two "ands". There is this extra hole next to the valve that supplies pressure to the bottom of the diaphragm (so the bottom of the diaphragm gets pre-throttle body air, while the top gets post-throttle body air).

 

Technically at boost, the pressure on both sides of the diaphragm is equal, so all that is counteracting the pressure applied on the valve is the spring force. Given high enough boost the spring force will be overcome.

 

If by design stock BPV was capable of holding any amount of boost, people could use it with GT35Rs... Well, they can with the "$0.16 mod".

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Technically at boost, the pressure on both sides of the diaphragm is equal, so all that is counteracting the pressure applied on the valve is the spring force. Given high enough boost the spring force will be overcome.

 

 

 

Your first sentence is opposed to your second sentence. If boost is equal on both sides of the diaphragm, then the only thing holding it closed is the spring pressure. If boost is equal on both sides, then it doesn't matter what the boost level is because the spring is always holding it closed.

 

 

The reason you don't see big turbo cars with stock BPV's is marketing and bling. My car only has a GT30r not a 35 so I guess that's why I can get away with the stock bpv.

 

 

edit: After re-looking at the nabisco thread... the OP of that thread doesn't even know what boost level he is at because his gauge max's out at 20psi. That's some quality tuning there.

(Updated 8/22/17)

2005 Outback FMT

Running on Electrons

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Your first sentence is opposed to your second sentence. If boost is equal on both sides of the diaphragm, then the only thing holding it closed is the spring pressure. If boost is equal on both sides, then it doesn't matter what the boost level is because the spring is always holding it closed.

 

You still don't get it.

 

It's not just diaphragm. There is also pressure applied to BOTTOM of the valve. Given high enough boost the valve will open.

 

http://i49.tinypic.com/281a0p3.jpg

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They still don't leak

 

+1... up to a point

 

measured the valve 5 years ago.

 

http://legacygt.com/forums/showthread.php/stock-bpv-measurements-92943.html?t=92943&highlight=BPV+measurements

 

granted, I only had one sample. there's likely a bunch of variation valve to valve which would explain why some hold and others leak at much lower pressures.

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They still don't leak

 

Until they do. Some people experience leakage at mild stage 3 (like VF52) levels.

 

But, anyway, do not let facts get in the way of your truths...

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+1... up to a point

 

measured the valve 5 years ago.

 

http://legacygt.com/forums/showthread.php/stock-bpv-measurements-92943.html?t=92943&highlight=BPV+measurements

 

granted, I only had one sample. there's likely a bunch of variation valve to valve which would explain why some hold and others leak at much lower pressures.

 

BBB, it looks like you have not taken into account the hole that supplies manifold pressure to the bottom of the diaphragm, essentially cancelling out the pressure supplied to the top via the skinny hose. Well, they probably do not exactly cancel each other out, because there may be difference in the area size (and due to pressure drop).

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I'm confused, did uclemat revive an old-ass thread just to rail on mwiener2?

 

:lol:

 

False information does not become any less false because it is year old :lol:

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Measure the spring pressure of the bov. That would be the maximum pressure our bov could hold before leaking based on your theory of how this thing works. What are you going to say when you find out that spring is only 8psi or so, yet these hold 18psi no problem?

(Updated 8/22/17)

2005 Outback FMT

Running on Electrons

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mic, you should really try to understand what's going on with the diagram and how air pressure applied on a surface is related to force.

 

http://www.challengers101.com/Pressure.html

 

if this were purely a piston based valve with pressure on the top and pressure on the bottom of the piston and both sides of the piston were of equal surface area, the forces would cancel out.

 

this is why the force of the red (against the diaphragm) and the force of the purple cancel out. because they are both pushing against the diaphragm which is the same size on both sides.

 

what doesn't get cancelled out is the force pushing upwards against the piston. the only thing counteracting the piston opening is therefore the spring.

 

and if you ever bothered to examine the piston on the stock bov, you'd discover that it's actually very strong and very hard to press open with your fingers. certainly more than 8 lbs.

 

to sum up: force trying to push valve open (from the bottom) is the sum of the force being exerted on the piston AND the force upwards against the diaphragm. force exerted in the other direction is the spring and the force downwards against the diaphragm.

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