I drive an 05 EVO VIII SSL and this week I finally installed my Forge Unos MBC. It holds ~21.75 PSI until redline without a problem, great MBC. My other mod is a full 3" TBE.

I've been reading and learning a lot about the EVO, and I agree that the stock BOV holds boost just fine at this level (~21.75 PSI), however, while driving today I floored my car on 3rd gear and when I was at about 7000RPM I took my foot off the pedal quickly, not gradually, and then give a little bit of gas again. When I did this my car jerked really bad. I may be wrong, but I think my BOV is not venting fast enough and it's keeping pressure on the system, does this make any sense? Also when I drive my car hard and shift it feels like when you drop the clutch too fast and the car jerks hard, but in reality I didn't dropped the clutch, I released it quite smoothly. These 2 things make me believe that the BOV is not releasing air fast enough when pressure is high.

I'd appreciate any input on this issue, I may be in need for a BOV replacement, if so my choice would be the APS.

Thanks.

 

You need a better BOV just to hold the boost better. What you see on the boost gauge has nothing to do with the BOV holding boost. It is leaking the whole time, and the turbo is working harder to maintain that boost level, which generates more heat, thus sapping efficiency.

The other stuff I don't know. I didn't have any such issues when shifting on my stock BOV. I ran 12.2 on it at 24psi shifting very hard above 7k rpm. The issues you're mentioning to justify getting a new BOV are not the typical ones we refer to when removing the plastic stocker. It's mainly to hold boost more efficiently, especially when boosting above stock levels like you are doing now. The APS gets good reviews. My suggestion would be the fully-recirculating Forge RS, which is adjustable. I just started using it this week in place of my MR DV.

 

MR DV for me. I traded up because of my reflash and wanted to make sure i knew it was doing its job.

 

I'm not trying to justify anything, I wouldn't want to replace the BOV, I'd invest that money on something else, like a flash. Before installing the MBC I never shifted at full boost because 21PSI didn't last too long, and when shifting boost was already at below 19-18PSI.

I thought about the leak possibility, but I think that if there is a leak, I should see a spike when accelerating hard, then boost will come down to a stable level. I see no spikes when I give gas quickly, it goes directly to a little bit under 22PSI and stays there the whole time.

My theory on the BOV not releasing enough air is because it feels like if there is still plenty of pressure on the system when I let off the gas or when I press the clutch. As I said I may be wrong, that's why I'm here to learn.

Another question, do we need to recirculate ALL air from the BOV? Why are there many dual-stage BOV options recirculating part back to the intake and another part to atmosphere?

Thanks.

 

I agree
I dont think a bov is worth the money and the problems associated with it.
I returned my Greddy RS, fluttered way to much, but I have heard that
units like Forge and APS work perfectly fine.

 

Got an APS if interested pm me

 

Got a Forge RS in anodized black for $150 if interested.

 

I just replaced my plastic one with an MR valve, and it works great. I can make my plastic one leak by blowing on it with my mouth, so it was obviously leaking quite a bit.

 

Nah, that thinking is all off base. Boost spikes have nothing to do with whether or not a BOV is leaking. A boost spike is natural depending on the MBC itself and the method by which you tap into the pressure source. I see a boost spike every time I roll into boost from low rpm. It always spikes then settles...very normal, since I have a Hallman and use the turbo nipple as much pressure source. You wouldn't notice your BOV leaking at all, because like I said, the boost is leaking right now everytime you go WOT, but you don't notice, because the turbo works harder to maintain the boost level you're trying to achieve. With a better BOV, you'd run the same boost levels, but the turbo would not have to work as hard, since nothing is leaking out through the BOV (or much less).

 

Stock BOV is designed to leak in conjunction with stock boost tapering setup, this is done by the provided piece of crap valve. Once you add boost controlling gadgets you wont get the desired air-tight system thats capable because the you still have the stocker.

The loss of boost however isn't going to hurt performance too bad until your setup for over 21 psi

 

You want to upgrade the stock plastic vavle to something better like the JDM MR or the Evo 9 metal version. I have noticed my stock bov leaking when I was pushing 21-22psi. Since then, I have changed to a JDM MR bov and the car is holding boost much better.

Thanks,
Tom

 

I think what you are experiencing is fairly normal for the stocker and also aftermarket bov's. I've had similar issues, but it's more due to your/my driving style than anything. If you "chop" the throttle relatively quickly, like trying to correct for oversteer, it happens. It's more pronounced running higher boost. Even if you replace the BOV to one that will release air sooner, you'll just feel the "jerk" sooner. The inlet and outlet of the aftermarket BOV's that recirculate are the same size as the stocker, you won't get more flow area necessarily, but maybe sooner release of the pressurized air depending on the spring rate. Again, it's not that the stocker is undersized, just a function of how it releases and how your driving style is.

 

Thanks to all for your help, I think all of you are correct. As stated above my BOV might be leaking, so I'll upgrade it. My choice so far is the APS. I have read plenty of reviews from EVO owners and none of them have complained. On the other hand my driving style could be causing this issue as well (as it was correctly pointed out), so I'll work that out a bit.

Now I have to find a good seller that has the APS BOV on stock, and at good price...

 

I thought my stock 03 diverter valve was doing O.K until I installed my new Forge RS valve several months ago. The first thing I noticed is that my part throttle/mild boost runs improved quite a bit. I also gained about 1.5 MPH in my trap speeds. It's funny that I bought the RS valve to prepare for future mods and always thought my stocker was doing fine.