Your bov spring should be as light as possible while holding closed at idle and holding boost up top. Any tighter is just going to kill your turbo. If your car is using speed density then opening at idle isnt even too bad except a small amount of unfiltered air but if it holds boost the kightest spring possible is best. That is why the factory uses a recirced valve so under heavy vacuum no unfiltered/unmetered air enters and the spring can be very light.

 

Hi Batty200, thanks for yr kind sharing and you mean i should turn back to a softer spring rate on my bov???

 

Thanks Ricardo...

 

As said, start by adjusting the bov.

Running without one is not the best idea. It will cause the air to bounce off the throttle plate and slam against the compressor blades.

 

I agree with everyone else. When the bov spring is too stiff it closes the bov too fast which causes air to be kicked back and cause surge. Terrible for your turbo.

 

1. DO NOT close off the BOV hole and make any runs. That will kill your turbo in a heartbeat!!
2. take out those stiff double springs and put the softest spring you can in the BOV.

If the spring is too stiff the BOV cannot respond to a pressure change when letting off the throttle. This will cause bucking and "surging" since the pressurized air has nowhere to escape to and reverses direction causing pressure to slap back against the blades on the turbo. This causes that "surging" you feel as the air tries to stop the blades from spinning abruptly.

Adding a stiffer spring may help keep the bov closed under high boost pressure but it can't do it's job correctly when you let off the throttle. As stated, go with the softest spring you can that barely holds the bov shut when idling. When you tap the gas you should see it slam shut fro teh vacuum/pressure change. The spring does not control the BOV under load, the vacuum/pressure does the work.

 

it happened when you changed the turbo and cams right? the s2's dont pull as much vacuum and vacuum is what opens the bov. bigger cams need a softer spring. i wouldnt run without the bov, just do what you can to soften up the spring rate.

 

Thank you so much Guys...I truly appreciate all yours sharing...+1

 

Don't forget to update us if this fixed the problem or not!

 

Will definitely do...Now it 3.30am over here...

 

I would suggest getting your Evo looked at by a tuner and get it retuned if you plan to use the stiffer springs. Also if you are running vta you should be on Speed Density if you are not then return to a recirculated setup.

 

Thanks Guys, and as Chinese New Year holiday is just 2 days ahead, will only able to update you guys next week.

But a kind forumer advise me to set my profec b II boost controller and he didnt mentioned abt the spring stiffness issue. He just ask me to slightly turn down my Gain and see how it goes.

 

Ive tried turning down my boost controller profec b II "Gain" and the most i can go down is 5% and its doesnt work...

Have took a short video but unfortunately its really too shrot but please pay attention on the beginning and you guys will see my boost meter goes hairwire just when i lift off the throttle a bit.
http://youtu.be/-Nn9OpKmECE

The boost was stable whenever i full throttle.

What happening??? Some forumers said my bov spring is too stiff and before i added the extra spring this problem is already there?

 

Unless there is a frayed wire, or a messed up vacuum line. I do not see how the profec could be causing it. I run the same boost controller and never had that issue. Post up all or your setting for it.

 

Ive a shared vacuum line for my Bov & Fpr from the intake.
2nd is another vacuum line from the intake to my boost controller and meter.

Ive tried swap Bov line sharing with the boost controller + meter and direct intake to Fpr but the problem still happen!

Btw, after i make the swap, my car started to knock...Even after i swap back to the previous arrangement the knocks does go away until ive to go for a fine tune again...