DOBSON DYNO TUNE
The main reason to run a blow-off valve is to stop back pressure against the turbo which can cause it to stall, or even bend and damage impeller wheels — in some cases they can actually snap off. There has always been a debate about where the BOV is placed in the system, but our preference is after the intercooler and before the throttle body, but it’s really a personal preference. In some applications such as high-power GTRs, we run two BOVs — one either side of the intercooler. The reason for this is to drop the pressure quickly when the throttle is backed off during racing. In other applications, such as some drag cars we’ve built, we don’t run a BOV at all, because our turbo supplier has specified this turbo is strong enough to handle the shock that can occur during surge. In some rally cars we don’t run BOVs to aid throttle response when getting on and off the throttle quickly, but often this shortens turbo life considerably — sometimes three turbochargers are used per season. We recommend they be run in all applications, but we generally listen to our turbo supplier, Steve Murch, as to whether or not he thinks the turbo can handle it, as he has had around 1000 years of experience. We find a lot of the time nowadays the BOV is purely cosmetic or for the noise, and this usually determines whether or not it’s plumbed back in. We don’t see any real advantage to running a plumbed-in unit, but when the vent-to-atmosphere unit is open for that short amount of time, it can let in dust and dirt as the valve goes back to its seat due to the vacuum created. During one D1NZ round-up in Whangarei, there was plenty of loose chipseal on the course, and a few turbos were destroyed — in some cases, whole engines. We believe there were five or six engines destroyed at that round — a big learning curve for a few teams.