Updated: Mar 17
(PLEASE NOTE, THIS DOES NOT APPLY TO THE VR30 IN THE NEW NISSAN Z AS THEY NOW COME WITH ELECTRONIC BLOW-OFF VALVES AND THE ECU LOGIC HAS CHANGED TO ACCOMODATE THEM. THINGS LIKE THROTTLE HANG ARE NO LONGER AN ISSUE BUT THINGS LIKE POOR FUEL TRIMS AND A ROUGH IDLE WILL STILL AFFECT THESE IF YOU PUT VENT TO ATMOSPHERE BLOW-OFF VALVES ON THE CAR WITHOUT THE ABILITY TO TUNE VE)
I see a lot of questions lately concerning blowoff valves for these cars. The simple and short answer is, they don’t work. Here’s why:
A typical turbo car, let’s say the GTR for instance, uses mechanical wastegates and recirculating blowoff valves to reduce boost when letting off the gas and sometimes between shifts. Whenever you see a GTR using a standard VTA (vent to atmosphere) blow off valve, you’ll find the car has been converted to speed density. It doesn’t use filter maf signals for fueling but a volumetric efficiency(VE)table precisely tuned by your tuner which doesn’t monitor active airflow but uses other calculations for proper engine fueling.
A recirculating blowoff valve is REQUIRED when used in a system that places the MASS AIR FLOW SENSOR(MAF) in front of the valves(which is how most systems are setup). A recirculating valve relieves pressure but doesn’t “waste” the airflow simply recirculates and pumps it back into the intake tract POST MAF) The reason for this is the MAF pre-fuels the engine which means ANY AIR passing by the MAF has to go into the engine. If it doesn’t, the ecu still adds fuel for that amount of air going into the engine. Extra fuel/less air= rich dips in air fuel. This won’t blow your engine up but it will cause your drivability to suffer and things like your spark plugs/AF sensors to degrade/foul over time.
The VR30 ECU’s logic is much different than the GTRs and other older systems. It uses the electronic wastegates and throttle bodies to limit/decrease boost. When you let off the gas, instead of relying on a recirculating blowoff valve (which is what it would need being that is a MAF car) to reduce spikes, it completely opens the wastegates and momentarily holds the throttle bodies open(sometimes up to 0.25 seconds) to give the small turbos time to slow down through exhaust turbine pressure relief NOT compressor pressure relief.
The two main reasons the VTA BOVs DONT work on these cars is because they are not currently able to be tuned in speed density and even after adding them, any pressure spikes you think you might be limiting, aren’t limited enough or even at all to make a difference in extending the turbo life due to the throttle body logic and how it hesitates closing once more than stock boost is added to the car.
In order for blow off valves to work, the valve has to be subjected to a positive pressure to vacuum condition to suck the piston up into the head of the BOV to allow air to escape the bottom portion of the valve. The throttle body logic limits this transaction completely and you end up with a small double spike every time. I have taken back to back logs and if I posted the boost pressure spikes after letting off the throttle, no one (including myself) would be able to tell you which log did and didn’t have the BOVs. The throttle let off spiking remained almost identical. This is something built into the logic that has yet to be(or able to be) solved by ECUTEK.