You guys are such a help, I won't stop now.

Is a BOV really needed? I will be tuned at 23psi. I have done alot of reading that pretty much says anything under 25psi and the BOV is just for show. What is the truth?

 

Without Bypass valve (diverter valve, blowoff valve, release valve or whatever else you want to call it) you will experience compressor surge. Compressor surge causes premature failure of turbochargers. Compressor surge occurs during off-throttle situations. As soon as the throttle is closed the compressed air that was flowing towards the throttle will boounce off of the closed throttle and reverse in a direction towards the compressor blade. The soul purpose of the bypass valve is to release this excess compressed air so it does not interfere with the compressor blades rotation. Recirculated diverter valve setups take matters one step further by recirculating the release air to the compressor's inlet which aids in the spooling of the compressor during shifts. So it doesn't matter if it's 1psi or 100psi, compressor surge will occur if the charged air is not released or recirculated. Recirculation is preferred on MAF equipped setups like the one on the EVO.

I'll try to dig up the drawings of this process.

 

Make sure you stick with a recirculating valve if you decide to swap the stock one out. I'm going with the Forge RS because there's no way the stock one will hold up to 30psi.

 

Hmm,when i bought my evo from a relative,it was already fitted with the SARD BOV,mileage is less than 10k Km.is this recomended or should i get rid of it... problem is i dont have the stock ones with me? should i change it to some other brand of BOV or am i just doin fine with the SARD ones? i'm really freaking out with leaks compressor surge and all....

 

If its already there, and it works okay, And its recirculated back to the intake, then its okay to keep it. If you find the car has drivability problems, then put a stocker or JDM valve on.

It turns out that for most people, keeping the stock valve works fine in most conditions.. If your boosting well over 22psi then it may start leaking a bit.


What is important is our cars use Diverter Valves, their still like blowoff valves, but the air that is released, goes back into the intake pipe. Without it recirculating, you release air that has already been "read" by the ECU, and by doing that, the car will run poorly when you shift, let off the gas, and at idle where the valve can be partly open due to engine vacuum.

 

Are there symptoms when the BOV is not working properly? Currently under load I can hear a release of air (my boost is not falling, so I don't believe it is a boost leak). I thought it was the BCS, but am wondering if it is the BOV. The air realease seems to be around 5K + RPM...

I am currently spiking at 24/25 and tapering to 21+ psi...

 

well your avatar says you drive a 9. Those are some of the best BOVs out there right now. IT should hold 23 psi fine since its the metal one and not the plastic one the 03-05s came with. Im sure if you pm warr he sould beable to tell you close to how much it will hold.

 

I have the same sound with the HKS SS BOV but I don't notice a drop in boost. Had an Audi A4 that made the same sound after X amount of RPMS until pop off. So either both BOVs are broke or its normal.