1JZ stock BOV

[Norbie]

Check what exactly?

If you mean how to check for a leaking BOV, disable it entirely and see if it makes any difference. If not, it obviously wasn't leaking to begin with.

[BigWorm]

I felt pretty silly when it turned out to be a dud hose clamp.

Hahaha, you noob!

[JZA70 R]

afaik turbo pressure is what kept the stock 1JZ bov's valve shut. using a very weak spring, manifold vacuum is what pulls the 'plunger' up to relieve pressure back into the intake.

hence the more boost pressure you run the harder the bov's valve stays shut. effectively making it impossible for it to leak under boost.

[Norbie]

If a BOV worked like that it would never open when you needed it to. Think about it, the maximum vacuum you'll get from the plenum is -1 bar (actually not even that), and on the turbo side the pressure can very easily spike to much more than 1 bar when you shut the throttle, even if you're running less than 1 bar boost. So -1 bar to open it and over 1 bar to keep it shut - guess which side wins?

[sheepers]

let me start by saying that i am on my 7th beer, so i take no responsability for what im about to say buuuut,
the second i close the throttle on my 1jz the boost guage goes into neg in a big way, there is this big flappy looking thing up the front of the inlet manifold and i reckon it stops the air going in. now, call me old fashioned but i reckon that might cause a bit of the old negative pressure. i guess that hose that comes from the inlet manifold round to the BOV must do something????

[JZA70 R]

norbie as soon as you get off the gas, you get vacuum in the plenum, as that happens your turbos fall off boost and there is no longer any pressure to hold the valve against vacuum so the valve opens...

have you see how the 1JZ bov gets pressure from where an a/m bov usually vents from?

[Norbie]

norbie as soon as you get off the gas, you get vacuum in the plenum, as that happens your turbos fall off boost and there is no longer any pressure to hold the valve against vacuum so the valve opens...

So you're saying the valve opens after the turbos have stopped making boost? If that's the case what purpose does the BOV serve? There's no boost to vent!

Maybe I'm stupid but I'm not following this at all. If the 1JZ BOV somehow works differently to all other BOV's, someone please explain how!

[JZA70 R]

No chances are im talking shit, i generally try to argue my understanding of something until im proven wrong. ...sometimes its the only way to get the facts straight!

[JZA70 R]

have a look at this Norbs... tell me what you think.

note: pressurised air is supposed to be fed through a 90' elbow hose that is disconnected in that pic. see how the bov appears to operate in reverse to a standard a/m bov?

[jonra23]

1. At boost and throttle open; there is same pressure in inlet manifold(where top hose comes from) and base of BOV so they cancel each other out, small spring holds BOV closed.
2. At boost and throttle snapped closed;have pressure drop in plenum and still boost pressure at base of BOV so large pressure differential which overcomes spring pressure and BOV opens.
3. Only 2 ways i can see a BOV can leak, it is mechanicaly faulty ie. seal damaged or physicaly sticking open or, there is a restriction in the inlet track that is causing a pressure drop between the BOV mounting point and where the signal hose plumbs in eg. way too small cooler causing restriction if BOV mounted pre cooler, pressure drop needs to be greater than the small closing springs pressure.

The units with 2 hoses are same principal but does not rely on pressure against BOV piston, has a Double sided diaphragm with pre throttle body pressure on bottom hose and post throttle body pressure on the top hose. Only possible advantage i could see would be that you can get the pre throttle body signal from somewhere other thn BOV is mounted.

regrads
jon

[JZA70 R]

Great Jon, are you talking about the 1JZ Bov in particular or just generic bovs in general?

[ReQuieM]

Yo, just a quick note, I'll elaborate tomorrow with pics. But Todds right the 1JZ bov works like the HKS SSQV. Compressed air comes into the bov and sits BEHIND the valve. A separate compartment controls the open/closing.

Peace out.

[jonra23]

Great Jon, are you talking about the 1JZ Bov in particular or just generic bovs in general?

They all work on the same pricipal, just packaged differently, original just do the job / low cost maufacture / generaly ultra reliable, aftermarket are shiny so more people buy them.

regards
jon

[ae86dave]

yes im a fan of the stocker cause of the stealthness and generally quiet sound

[ReQuieM]

Ok here goes. In the pic below. 1 line to front(closest to valve) chamber. this has a small filter/one way valve in line with it. Origanly I thought it was a one way vavle but when I tested it again yesterday I could get air through both ways, blow suck, but one of the connectors that was broken when I removed it earlier so it may have effected the proper workings of it. One way was more difficult I forget which. Blowing into line 1 opens the vavle.

2 is straight into the larger rear chamber. both 1 and 2 feed from the same line which I believe comes from the plenum. Sucking on line 2 opens the vavle.

3 is the pressured air entry. 4 is back to the intake. In the second photo you can see that the air enters the bov and rest BEHIND the valve, just like a cylnder head.





SO from what I can tell it is set up just like the HKS SSQV being that it is a NON piston BOV. Alough it lacks the adjustability that the SSQV has. inside the Sealed chambers will be a spring pushing against a diaphram, which is the wall beween the two chambers. I'm going to assume that the in-line filter was some type of slow release valve or filter? I cant see how a one way would help in this situation UNLESS there is a valve in the diaphram to allow air to enter or exit the second chamber. Basicly under vaccum the spring compresses and teh valve pulls back and opens alowing the air back into the intake track.

The good thing about this set up is that it wont leak. the bad side is that under high boost it wont open. Possible factor in turbo breakage at high psi? If pressure is applied back on the turbo to attempt to make it spin the other way while under load (gear change while gunning it), no bov or malfuctioning one, the weakest link would have to be the ceramic blades on the turbine. Food for thought I guess.