This is a quick observation regarding the effects of replacing the OEM bypass valve with an aftermarket bypass/blow off valve. In general aftermarket BPVs don’t add much performance unless you plan on running 20+ psi on the MazdaSpeed platform. At this boost level pretty much all OEM valves start to open and bleed pressure. On vehicles with a big turbo this can be a little hard to detect as the turbo is able move much more air than the OEM turbo. Big turbo cars will still hold boost (see boost curve on the dyno plot below) but airflow (g/s) values will seem low as will power. On the car below we were in the middle of a pump gas tune on a BNR S3 when the OEM BPV was replaced for an aftermarket unit. The motor had a lot of miles on it and was knock prone but you can see what replacing the OEM BPV did to the vehicle’s performance. This is why we believe it is wise to run an aftermarket bypass valve on tunes where you will be holding boost levels in excess of 20psi as well as all big turbo tunes.

We carry one of the the best BPVs on the market for the MazdaSpeed here.

Aftermarket Vs OEM BPV