Originally Posted by Brett@GFB

I’m assuming from your question that you’re trying to determine if your valve is “leaking boost”, would that be correct? The reason I ask what may seem an obvious question is that the term “leak” should be used in context, i.e. in conjunction with a magnitude. For example, your test of applying boost pressure to the nipple and detecting a leak out of the outlet ports does show a leak, but I guess the real question is “does this leak affect the BOV’s performance and its ability to hold boost pressure?

Much like the pistons in an engine, there will always be a small amount of “leak down” past the piston from the top chamber to the outlet ports – this is unavoidable on any valve that vents to atmosphere because a prerequisite of venting to atmosphere without idling problems is almost zero friction of the piston movement. It would be possible to seal the piston 100% using an o-ring, but unfortunately o-rings (no matter how loosely compressed) will always cause friction, which will severely compromise a valve’s performance when venting to atmosphere, leading to stalling and backfiring issues.

I can say with 100% certainty that the leak you describe won’t cause the valve to open under boost, cause the boost pressure to drop, or change the air/fuel mixture. I can say this with such certainty because of the following. The valve you have will remain closed as long as the pressure at the top is equal to or no more than about 6psi less than the boost pressure in the intercooler pipes – this means the leak would need to be large enough to cause the pressure in the top of the valve to drop more than 6psi below the intercooler pressure in order for the valve to open under boost. Unless this happens, the valve simply will not open.

A leak large enough to cause a 6psi pressure loss in the top of the valve would also render the valve inoperable – i.e. when you lift the throttle there would not be enough vacuum to open it and it would not vent. In fact it takes less of a leak to prevent the valve from venting when you lift the throttle than it does to allow if to lift under boost, so therefore if the valve blows off normally when you lift the throttle, it can be said with confidence that it is not opening under boost.

Now, the leak itself – does this affect boost pressure? If the valve vents normally as per the above, no. A leak that causes a loss of boost pressure, or that can even be measured as a percentage of the air that the engine consumes needs to be pretty big, like something about the size of an 8mm hole or so. As a comparison, a boost control solenoid or bleed valve typically leaks about 10 times more than the amount of air that leaks down past the piston on the BOV. Of course, without being able to see the valve I cannot say for sure if the amount of air you have leaking out is within what I would say is a normal range, but I can say for sure that the above argument about its operation is still valid – i.e. the valve will continue to work properly even if the leak were larger than normal.

In a nutshell, to confirm the BOVs operation you can do the following:

* Check if the valve vents normally when you lift the throttle, if yes, then even if it does show an air leak by bench testing or smoke testing, it will not cause a boost pressure drop or affect the car’s performance in any way.
* To further confirm, you can measure the boost pressure at the manifold, and then measure it in the BOV vacuum hose. If there is a difference of less than 6psi, it can be safely assumed the valve is not opening under boost.


I hope this information helps, but of course as I have made a few assumptions along the way please feel free to comment if they are incorrect. If the leak is exceedingly large but the valve still operates normally, it is possible some damage has occurred to the piston that can be easily fixed. A very non-scientific method to use to determine if the leak is within a normal range is to suck on the vacuum nipple. If you can pull a vacuum and hold it for a few seconds, then it will undoubtedly fall within the normal range. If you cannot hold a vacuum at all (i.e. can draw breath through it), then I would say it probably should be looked at for peace of mind.

Let me know how you go with the tests, or if you have any further information about relevant symptoms please let me know.

Originally Posted by Brett@GFB

he good thing about the EVO X is that it runs a hot wire type MAF sensor which is less sensitive to BOVs than the Karman Vortex type found on the earlier EVOs, so you have more flexibility on the BOV settings.
Our testing has shown that best throttle response is achieved with firmer spring settings, which typically only allow the valve to start venting when the car is being driven in a “spirited” fashion. This is because a firmer setting will hold slightly more pressure in the intercooler and pipes during a gearshift, and hence shorten the time it takes to get back to full boost when you re-open the throttle (not really an issue if you have the SST model though since you don’t lift the throttle to shift). This will however increase the amount of flutter you get when rolling off the throttle slowly, or lifting off before the turbo has fully spooled, but as long as that noise doesn’t bother you, there is no harm in setting it up this way and there is a small improvement to be had.

Best regards,
Brett Turner B.Eng. (Mech)
Design Engineer
Go Fast Bits
Phone: +612 9534 0099
Skype: brettturner77
brett@gofastbits.com.au
www.gofastbits.com.au

Originally Posted by solarevo

i have a forge rs and have not had a single issue, plus i dont have the ricer pssssshh sound

Originally Posted by Clipse3GT

You must be the chosen one, since everyone else on here has issues with the FORGE RS.