Standard Recirculation Valve Removal
What is the dump valve and why remove it? SXOC member Nick Kudrycz explains much better than I can.
"This is the valve that releases compressed air from your intake when you take your foot of the throttle. Nissan fitted this as standard to help meet emissions standards and also to prevent the lovely rally-esque flutter noise. This noise is created as the compressed air does an about-turn back through your spinning turbo blades
The standard dump valve is believed to leak at around 1 bar (14.5psi) and your options are to buy an aftermarket one or to get shut altogether.
Removing the valve *should* be safe when running relatively low boost pressures (< 1.4bar) although some really good information can be found here if you're unsure. Note: I wouldn't recommend doing this if you still have your Cat fitted. Without a fuelling computer, your car will overfuel on lift-off causing unburnt fuel to pass through into the exhaust system and could foul the Cat."
Listen to a pigeon in flight!
Running without a DV/BOV at high boost (15psi+) may cause damage to your WMIC/FMIC due to back pressure.
Before doing this mod, you must have something to block the intake and out-take pipes, as well as the small actuating pipe. I bought two aluminium plugs (27mm and 30mm diameters) from SXOC member 'Mark' for this purpose. They are, however, available from other sources. I used a small bolt to block the 10mm actuating pipe.
You should only need 8mm (for the jubilee clips) and 10mm sockets, but a flat-head screwdriver may come in handy for unclipping things. You will need to remove the battery to allow proper access to the dump valve.
First, unbolt the pipe marked (2) in (Figure 1) from the rocker cover. It will be held by 10mm bolts. You will also need to unclip the cable attached to it. Undo the jubilee clip marked (3) and remove pipe 2. This pipe is attached to the dump valve at the other end (1).
Taking a closer look at the dump valve (Figure 2) you can see three pipes attached to the dump valve. First undo the clip holding the out-take pipe to the dump valve and lever it off. This is the other end of the pipe you unbolted from the rocker cover. You should be able to completely remove it now. Next, loosen the pinch clip on the actuating pipe and disconnect it. Finally, undo the jubilee clip at the opposite end of the intake pipe to the dump valve. Unbolt the dump valve from its mounts and twist it forward. This will allow the plastic end of the intake pipe to come off and you can remove the valve and pipe.
Figure 3 shows the removed pipes and dump valve.
Figure 4 shows the two plugs required to block off the intake and out-take holes. The out-take is 27mm and the intake 30mm.
The intake plug will be subjected to a great deal of pressure under boost and people have encountered problems with them shooting out. For this reason I would advise sealing it in with some Superglue or silicon sealant then tightening the jubilee clip firmly. Use a small bolt or screw for the actuating pipe and reapply the pinch clip. Tuck or tie the actuating pipe away from the fan.
Insert the out-take plug and tighten the jubilee clip.
Replace the battery and you're done. One racing pigeon released!