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Bad Bov Behaviour? (Leak Question Again)

zoomzoom

By zoomzoom,
in Engines & Forced Induction

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zoomzoom Mentor

zoomzoom

Posted
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I have been pressure testing my intake (1996 RB25DET) as I was fairly sure I had a boost leak, and surely enough on pressurising the crossover pipe, the BOV was noticeably leaking - back into the recirculation pipe that is.

My understanding is that the pipe from the manifold should provide enough pressure + the BOV spring to keep the BOV sealed under boost. Upon further testing, it only makes a small difference whether that side of the BOV is massively pressurised (like 40psi), or open to atmosphere. In either case the BOV still leaks when the intake is pressurised.

My car cannot create more than 6-7psi so this will hopefully go a long way to fix that. I am concerned that the turbo is working overtime to compensate for any pressure leaking, rather than wanting more boost.

paulr33 Grand Master

paulr33

Posted
Posted

from memory its designed to leak at idle

its a design feature, not a problem

the bov's main function is to slam open when pressure spikes it's ass off in the pipework, ie sub 40psi+ like you said

i cant see how it leaking at idle (as intended) would cause a problem

whats the issue you are trying to resolve

zoomzoom Mentor

zoomzoom

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No I wrote that the BOV leaks regardless of the pressure on the connector which goes to the manifold. eg even with 40psi supposedly keeping the BOV shut, the BOV was leaking a lot of air.

I can understand why it would let air pass at idle - less than atmosphere pressure in the manifold should allow the diaphragm to bleed.

The problem is my car has trouble making more than 6-7psi of boost. You can even run an open wastegate and it wont boost past that (only tried that at low revs)

I dont know if its a combination of issues. Could be the wastegate itself isnt holding, but I thought I would do a simple pressure test first, and the car failed.

zoomzoom Mentor

zoomzoom

Posted
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Perhaps unfortunately, the BOV and intake is working just fine, meaning I have a more involved problem with the wastegate or something.

For those interested, that little hole on the BOV helps to open the valve. ie when its pressurised the valve opens. No doubt part of the quick release system when you take your foot off the accelerator while on boost. I wouldnt want to block it, even if it is a boost leak technically.

KiwiRS4T Grand Master

KiwiRS4T

Posted
Posted

GTR bov bolts on in the same place but the outlet hose is bigger - easy to adapt I have one on my Stagea. GTR bov is better made (you'll see when you look at it). What are you using for boost control? Usually even with just bigger exhaust and better i/c you will hit 10psi. If you have no boost controller at least by pass your solenoid:

This is the 10 minute no cost boost to 0.5 bar rerouting of the vacuum hoses [thanks to SK]. Disconnect the two vacuum hoses from the solenoid. Then connect the boost feed (from the cross over pipe on the left of the picture) to the standard T piece. Connect one side of the T piece directly to the wastegate actuator (on the right of the picture). The remaining connection on the T piece goes back into the inlet via the BOV return pipe (on the standard fitting). Make sure to put the standard brass restrictor in that vacuum hose to bypass the desired amount back into the turbo inlet. The standard bypass hole of 1.25 mm bypasses enough air flow for 0.5 bar. (See photo)

PS: If you want more boost you can drill out the bypass, 1.5 mm = more boost (around 0.7 bar) 1.75mm = a bit more (around 1.0 bar).

OK, this is the picture of the vacuum hoses. The boost pressure comes out of the intercooler return pipe (that's the big black one on the left) via the standard fitting. It travels down the vacuum hose to the standard T piece.

The right hand side of the T piece goes to the wastegate actuator via another short piece of vacuum hose. It has 2 standard spring clamps on it. So that "some" of the boost pressure goes to the wastegate actuator.

The left hand side of the T piece is connected to another (longer) piece of vacuum hose that goes to the standard fitting on the BOV return pipe. You can't see that fitting in the picture as it is hidden by the (big black) turbo to intercooler pipe. I squeezed the standard restrictor into that vacuum hose, it is tight fit, so be patient and use some lubricant (RP7 in my case).

The restrictor limits the amount of boost pressure that is bled off, so that the "some" pressure that goes to the wastegate actuator is actually less than the boost pressure. This means you get more boost before the wastegate opens at its usual 4-5 psi. How much more depends on the size of the hole in the restrictor, the bigger the hole the more it bypasses and the higher the boost.

The standard hole is ~1.25 mm and gave ~0.5 bar on my Stagea, which has standard everything else (no exhaust, no FMIC, std filter, etc). If you have mods, you may not get the same boost pressure, so you may have to adjust the size of the hole in the restrictor, it is brass so you can easily solder it up and redrill the hole smaller if necessary.

scotty nm35 Grand Master

scotty nm35

Posted
Posted

Perhaps unfortunately, the BOV and intake is working just fine, meaning I have a more involved problem with the wastegate or something.

For those interested, that little hole on the BOV helps to open the valve. ie when its pressurised the valve opens. No doubt part of the quick release system when you take your foot off the accelerator while on boost. I wouldnt want to block it, even if it is a boost leak technically.

I blocked mine, it can cause issues with part throttle coming off boost but nothing bad. Just tap an m5 thread and grub screw it, that way its easy to remove if you don't like it. How were you pressurising the intake?

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