Nissan 200SX Club - South Africa

Hey Guys,

This might be a stupid one but here goes n e way.
As far as I have read up you use a BOV to blow off excess boost to keep your turbo spooled.

I also heard the other day from somone that you should set it p to keep pressure in the system so that you dont take so long to get back upto pressure.

Now this to me is a bit of a conflicting statement though. Where would you find the balance between keeping pressure in the system and blowing it off to keep the turbo spooled ?

If anyone has heard of this and can explain it to me I would be HIGHLY greatfull

<edit> O and P.S. What you guys think of Tial BOV's ?

As far as I understand a blow off valve does exactly that. It blows out the pressure build-up inthe system. When you close the throttle the pressure cant go anywhere and the flow through the system stops. the only way it could go (the pressure that is) is back through the turbo. This can stop and even backspin the turbo. (VERY harmfull and could snap the turbo shaft off) The blow off valve is thus to protect the turbo and also to help spooling through letting off the pressure build up.

Once the pressure before the valve (Boost) and behind the valve (vacuum) is about equal the valve closes (Spring pushes it closed)

Once you open the throttle again and the vacuum that formed in the manifold becomes boost the valve stays shut and allows boost to build.

Theory says that to enhance flow through the system placing the BOV closer to the throttle body is better since the pressure does not need to change direction to exit via the hotpipe but instead flows through the system in the same direction also enhancing spool up time. you can however fit 2 BOVs one close to the turbo on the hotpipe and one close to the throttle body.(which has a neutral effect)

i run 2 bov one on the hot pipe and one on the cold pipe the exit of the bov runs directional to my air flow so like he said doesnt change direction

To also increase the flow effect you can run the one on the cold pipe much smaller. The "gas" will move towards the side with least restriction.

To answer your question re Tial blow off valves - Very good as far as I have heard. Was however designed for large capacity systems/high boost levels.

A good setup would be a HKS SSQ on the cold pipe and a Tial or similar large capacity BOV on the cold pipe as close to the throttle as possible. with the 2 connected in parallel (on the same vacuum line). Place the BOV on the hotpipe on the longer end of the line - will cause a delayed reponse helping the flow direction in the system.

Please note that these are for longer gear changes. once you change gears quickly and get back on the gas the valves will shut and there will still be pressure in the system. I would only recommend this on large capacity high boost applications otherwise you are just wasting money. Rather fit 1 really nice and good BOV and be done with it and when you do place it on the cold pipe.