Guest Posted October 19, 2013 Share Posted October 19, 2013 ^ Right on. It's likely that the surface area of the bottom of the diaphragm is actually smaller than on the top - to allow for the piston shaft. In other words the downwards force on the top is bigger than on the upwards force on the bottom. So it is possible it takes some more pressure than the spring rate to open the valve. However, the stock USDM BPV's spring is indeed much stronger than 8 lbs. Since the JDM STI BPV design is different (and works more like mwiener2 think the USDM one works), it's spring is much weaker - does not need to be as strong, since there is no pressure is applied to the bottom of the diaphragm (or, more correctly only atmospheric ressure is applied). Link to comment Share on other sites More sharing options...
bugblatterbeast Posted October 20, 2013 Share Posted October 20, 2013 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). that was the whole point of the measurement I took, unless we are talking about different things. the reason I added the different cracking pressure estimates based on the pressure drop between the spot the BOV sits at and the manifold is because I was accounting for the pressures on either side of the actuator diaphragm. the unbalanced force due to the difference in pressure across the diaphragm was added to the force due to boost pressure on the valve, then subtracted from the spring preload. the best case is one where the BOV experiences the same pressure as the manifold. in that case, the force from the diaphragm is nearly zero and the valve is held shut by just the spring. for that case we just need to deal with the area of the valve subject to boost pressure and the spring preload. if there is pressure drop between the spot the BOV sits at and the manifold, the force on the diaphragm serves to effectively drop the spring preload, with a commensurate decrease in valve cracking pressure. I did eventually xray the part and confirm the sizing, but that was years ago. the actual sizes were close to my initial estimate based on external measurements so I never bothered re-calculating things. Link to comment Share on other sites More sharing options...
bugblatterbeast Posted October 20, 2013 Share Posted October 20, 2013 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? the measurements I took 5 years ago kinda support this. there's a difference in the explanation for the effect though. if you pull the pressure reference line, the valve opens really early. you have (boost pressure - atm pressure) acting over the diaphragm area, decreasing the preload on the valve. the calculated cracking pressure was around 6 psi and the field test indicated max boost around 8 psi, which is roughly inline with a valve cracking at 6 and quite a bit more open at 8. but this isn't because the spring is light. it is because the difference in pressure across the diaphragm is subtracting from the preload the spring was giving. a direct measurement of the preload and area would give ~28 psi cracking pressure, but that is assuming the pressures on both sides of the diaphragm are matched. in normal operation, as long as the throttle plate is open, both sides of the diaphragm see nearly the same pressure. this is why the bo valve is able to stay shut at higher boost pressures. Link to comment Share on other sites More sharing options...
Guest Posted October 20, 2013 Share Posted October 20, 2013 BBB, ok it was not clear from your old post. The 28 psi is the ideal case, right? Due to the pressure drop and the presumed variance in BPV stock rates, it be would be the explanation for the leakage at lower (<20 psi) boost levels? Link to comment Share on other sites More sharing options...
mwiener2 Posted October 22, 2013 Share Posted October 22, 2013 Take a balloon and put it on the outlet of the stock BOV... Floor it, see what happens. Report back. My Mods List (Updated 8/22/17) 2005 Outback FMT Running on Electrons Link to comment Share on other sites More sharing options...
Guest Posted October 23, 2013 Share Posted October 23, 2013 Phew. Before giving any advice admit you had no clue how the stock BPV worked... Link to comment Share on other sites More sharing options...
mwiener2 Posted October 23, 2013 Share Posted October 23, 2013 No, because it doesn't leak. And it's still always spring pressure over boost, even with your newly discovered mode of operation. Otherwise it would always leak over 8psi. Which it doesn't. My Mods List (Updated 8/22/17) 2005 Outback FMT Running on Electrons Link to comment Share on other sites More sharing options...
Guest Posted October 23, 2013 Share Posted October 23, 2013 The spring is not 8 psi Link to comment Share on other sites More sharing options...
mwiener2 Posted October 23, 2013 Share Posted October 23, 2013 Then what is it? My Mods List (Updated 8/22/17) 2005 Outback FMT Running on Electrons Link to comment Share on other sites More sharing options...
iNVAR Posted October 23, 2013 Share Posted October 23, 2013 http://legacygt.com/forums/showthread.php/upgrading-stock-bpv-hold-20-psi-131596.html a while back I thought mine was leaking so I made some measurements on the unit. The valve diameter is about an inch and the spring preload is over 23 lbs. assuming there is no pressure drop between the port drilled into the IC side flange and the small hose nipple, the force from the actuator is solely from the spring. under these conditions, it takes ~29 psi just to crack the valve. at partial throttle I can see there being enough of a pressure drop between the two points to greatly lower the cracking pressure, but the boost targets shouldn't be that high at mid throttle anyway. at WOT, I can't see there being a big enough pressure drop to significantly lower the cracking pressure. that being said, there's probably a fair bit of preload variation from unit to unit.But don't take his word for it. Push on it with your fingertips with all your might. With any luck, you'll hurt your fingers and stop posting for a while. Link to comment Share on other sites More sharing options...
mattg Posted October 23, 2013 Share Posted October 23, 2013 ^ hehe Link to comment Share on other sites More sharing options...
Guest Posted October 24, 2013 Share Posted October 24, 2013 http://legacygt.com/forums/showthread.php/upgrading-stock-bpv-hold-20-psi-131596.html But don't take his word for it. Push on it with your fingertips with all your might. With any luck, you'll hurt your fingers and stop posting for a while. It still will be 8 lbs, even if he broke his fingers... Link to comment Share on other sites More sharing options...
BrandonspecB Posted October 24, 2013 Share Posted October 24, 2013 I'm really interested in knowing how well the stock bpv works. I love having an oring instead of a gasket. I'm going to build a tester tomorrow after work and I'll post a video to show the pressure it opens at. Link to comment Share on other sites More sharing options...
BrandonspecB Posted October 24, 2013 Share Posted October 24, 2013 Here are some testing vids I made. My stock BOV may be broken. It lets a lot of air past at 10 psi. The Turbosmart lets out an acceptable amount of air. Stock http://i1231.photobucket.com/albums/ee505/bkatter/BOV%20testing/th_StockBOV.jpg Turbosmart http://i1231.photobucket.com/albums/ee505/bkatter/BOV%20testing/th_Turbosmart.jpg Link to comment Share on other sites More sharing options...
iNVAR Posted October 24, 2013 Share Posted October 24, 2013 ALL BOVs leak to some degree. It's a moving part (piston) and thus must have just a tiny bit of clearance between between the walls. The question is what is the rate at which you leak? BTW, thanks for the video. Link to comment Share on other sites More sharing options...
SeeeeeYa Posted October 24, 2013 Share Posted October 24, 2013 Here are some testing vids I made. My stock BOV may be broken. It lets a lot of air past at 10 psi. I'm really disappointed in my Turbosmart. It lets air past at 10 psi, though much less air than the stocker. If you listen close you can hear the pressure release when I lift my hand off the outlet. Pretty sad. Stock http://i1231.photobucket.com/albums/ee505/bkatter/BOV%20testing/th_StockBOV.jpg Turbosmart http://i1231.photobucket.com/albums/ee505/bkatter/BOV%20testing/th_Turbosmart.jpg Modify the stock OEM valve. Redo the test. Report relative results. Link to comment Share on other sites More sharing options...
BrandonspecB Posted October 25, 2013 Share Posted October 25, 2013 ALL BOVs leak to some degree. It's a moving part (piston) and thus must have just a tiny bit of clearance between between the walls. The question is what is the rate at which you leak? BTW, thanks for the video. You're welcome. I love testing things and sharing the results. You are right about air getting past the piston. I never thought about that. The Turbosmart doesn't have a diaphragm, so the air presses directly on the back of the piston. The air leaking isn't getting past the o-ring seal at the bottom of the piston, but rather getting around the sides of the piston from the top. So it is definitly an acceptable leak. I changed my comments in the previous post to reflect that. I'm happy with it again I disagree that all BOVs leak to some degree. I had a recirculated Tial Q on a different car that wouldn't let any air out during 35 psi boost leak tests. On to the new tests. I did all of them again, but this time I tested the Turbosmart to a higher pressure and tested a modded stocker. Stock test #2 http://i1231.photobucket.com/albums/ee505/bkatter/BOV%20testing/th_StockBOV2.jpg Modded stock valve http://i1231.photobucket.com/albums/ee505/bkatter/BOV%20testing/th_ModifiedStockBOV.jpg Turbosmart test #2 http://i1231.photobucket.com/albums/ee505/bkatter/BOV%20testing/th_Turbosmart2.jpg Link to comment Share on other sites More sharing options...
SeeeeeYa Posted October 26, 2013 Share Posted October 26, 2013 Modded OEM, sixteen cents (or nothing if you're clever), with OEM reliability. Improved driveability with no psi limits, but no bling. Served me perfectly. Excellent testing/posts, BKatter. Link to comment Share on other sites More sharing options...
hadvw Posted October 26, 2013 Share Posted October 26, 2013 Does this need a re-tune due to higher flow at high psi? What kind of psi could a bnr16g realistically flow with 650cc injectors, walbro, only the last cat left in the pipes? My lgt20dig is reporting up to 21 psi at times, but the sensor max is around 22 psi, IIRC, so I'm not sure if I'm hitting the sensor limits or not.. Link to comment Share on other sites More sharing options...
05.5abpLGT Posted October 26, 2013 Share Posted October 26, 2013 Im currently running the bnr 16g evo3 on stock injectors, pump, and stock bov (with this mod) and it occasionally see's 20-21psi and does fine with it. Link to comment Share on other sites More sharing options...
iNVAR Posted October 26, 2013 Share Posted October 26, 2013 I disagree that all BOVs leak to some degree. I had a recirculated Tial Q on a different car that wouldn't let any air out during 35 psi boost leak tests. Sorry, I should've been more specific. All piston based diaphragm-less BOVs leak to some degree. Don't really understand why your stock unmodded BOV is leaking that much though. That sounds like a pretty insane amount... Link to comment Share on other sites More sharing options...
mwiener2 Posted October 26, 2013 Share Posted October 26, 2013 I guess everyone's idea of the size of leak is different... My Mods List (Updated 8/22/17) 2005 Outback FMT Running on Electrons Link to comment Share on other sites More sharing options...
GTTuner Posted October 26, 2013 Share Posted October 26, 2013 A leak is a leak in my book, Forge is a nice product for the price. Screw the $0.16 mod. BUT my stock BOV/BPV held 18 psi reliably. Link to comment Share on other sites More sharing options...
Mega Users seabass07 Posted October 26, 2013 Mega Users Share Posted October 26, 2013 I guess everyone's idea of the size of leak is different... Link to comment Share on other sites More sharing options...
SeeeeeYa Posted October 27, 2013 Share Posted October 27, 2013 The value of the sixteen cent mod lies in what it does to the engine characteristics commonly termed driveability, not the absolute and sole reference to pressure containment. How much it does or does not leak is important, but a side consideration as most day to day driving is done at less than WOT, and indeed the boost involved may lie within the OEM BPV's ability to contain it. Those who keep the OEM BPV stock will not understand. A Forge valve does the same thing, set up properly. But it costs a lot more than sixteen cents to nothing. Those with these valves are aware of what it does to driving characteristics. Vehicles with per-gear tuning, where full boost is available in first gear on up, are essentially hobbled by an unmodified OEM BPV or lack of proper AM valve. Those satisfied by the unmodified OEM BPV system are satisfied by pedestrian performance. While everyone is entitled to their choice without criticism, what is discussed here is measurable comparative phenomena. Logging measures relative differences. It is what it is. Link to comment Share on other sites More sharing options...
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