1JZ stock BOV

[ReQuieM]

Rather then whore someone elses thread I thought I'd start another.

What PSI can the stock 1JZ bov handle before it starts to leak or malfunction?
Any real world experince of it causing issues?

[ReQuieM]

Is this a stupid question?

Or does nobody know because they haven't boosted the stock BOV enough to have it leak?

[beasht]

I *think* they start to leak at about 15-16psi but as with most things, some people can run there turbos at 18psi all day everyday while others die at 10psi you can't put an exact figure on it. Mine leaked a bit at 14psi before I dumped the boost down to 10

[Norbie]

There's no real answer to your question; the point at which the stock BOV leaks depends how much pressure drop there is between the turbo and the plenum. This obviously varies considerably depending on your inlet piping and intercooler setup.

[BigWorm]

It would also be pretty hard to verify I reckon, considering the stock BOV is plumbed back. The only way I can see checking is to have the car on a dyno & putting your hand over the BOV outelt. Otherwise you're hardly going to hear it leaking when the motor's at full noise.

[Norbie]

Actually a leaking BOV makes a hell of a whooshing noise at maximum boost - I've heard it on a number of occasions.

[BigWorm]

So, I'm guessing we're talking about your car?
In which case, how do you know it's the BOV, and what boost where you running? (the stock 2J BOV looks to be half the size of a 1J BOV, so could technically hold more pressure with a smaller piston surface area? But then the diaphragm would also be smaller, but then the difference in size difference would be smaller. I guess leak thresh hold would be pretty similar, only flow would change..... Don't mind me, I'm just thinking out loud )

[Norbie]

No we're not talking about my car... and I don't have a stock BOV either.

[ReQuieM]

Norb, I mean leak as in unwanted venting during spool not how much it vents CFM air wise. Sorry but your answer seams to be reffering th amount vented, either that or I'm not getting what your saying, which is probably it. Example being turbs pumping out 16 PSI and the spring/vavle/dia isn't strong enough to hold that 16psi so it starts to vent that pressure back. -Just to clarify my question.

OR are you saying theres no way to tell because most guages read from the plenum side and the actual PSI on the turb out let is higher due to restriction?

There is obviously a point where pressure pushing on the valve/piston is more powerful then the spring/whatever holding it shut. That is the point I'm wanting to know.

[Norbie]

I know exactly what you're talking about and I answered accordingly.

Inside a BOV you'll find a piston with turbo pressure on one side and plenum pressure on the other side, with a fairly weak spring to keep it shut by default. When the pressure differential on either side of the piston is large enough to overcome the pressure of the spring, the piston moves and allows air to escape.

Note the words pressure differential, this is fundamental to how a BOV operates. The absolute pressure doesn't mean diddly, and that's why I answered your question the way I did.

[ReQuieM]

Ok, I've only had experience with the HKS SSQV. Similar idea to what you say but the pressure in the pipe holds the piston/valve shut. IE pressure on the reverse side, rather then against it. The plenum pressure is then in a separate chamber, so only vaccum opens the piston not pressure diferential.

Now I understand what you mean by the pressure differential. In theory if there was a major restriction then beefing up the spring could help reduce the leak.

Cheers Norb.

[ReQuieM]

Sorry not allowed to give the gift rep.

[BigWorm]

No we're not talking about my car... and I don't have a stock BOV either.

Meh, I thought you had an aftermarket BOV.....
So what car are you talking about, & how did you know it was BOV leakage?

[Norbie]

I've heard it on a couple of cars actually, one was an MA70 with a 1JZ (stock BOV) and the other was a VL with some massive ricer valve. In both cases it was because the pressure reference line had popped off the BOV, so it was opening whenever the turbo came on boost. Interestingly it was still possible to get 7-8psi boost if you kept into it but the whooshing noise was incredible, there was no way you could miss it!

Oh and for the record my stock 2JZ BOV never leaked, I installed the aftermarket BOV because I mistakenly thought it wasn't flowing enough air and that's why my cooler hoses kept popping off. I felt pretty silly when it turned out to be a dud hose clamp.

[ae86dave]

so what would be the best way to check?