When Should I Upgrade My EcoBoost Mustang Blow-Off Valve?

A blow-off valve is a part that is common to most turbo systems. When you are boosted while accelerating, the intake system post-turbo is pressurized. As you shift the car and let off the gas, the throttle plate closes and all that pressure slams into it. With the throttle plate closed and nowhere else to go, the pressurized intake charge is forced back towards the turbo. When this air gets to the turbo, it slams into the compressor wheel. This is called compressor surge, and it can damage your turbo over time, cause the compressor wheel to stall out, or increase turbo lag while the compressor recovers from the surge. Having a good blow-off or bypass valve is the key to a happy and healthy turbo set up.

There are a few different types of blow-off valves. There are true blow-off valves, compressor bypass valves, and hybrid valves. True blow-off valves vent directly to the atmosphere and create the WHOOSH sound everyone is familiar with. These will cause a slight rich condition on an EcoBoost Mustang because the air being released has already been measured and accounted for by the MAF. Compressor bypass valves allow the pressurized charge to be returned to the low pressure side of the intake, so the engine will not run rich when letting off the throttle. Hybrid valves are a combination of the two, releasing some pressure to the atmosphere and returning some pre-compressor.

• Blow-off valve: Vents all boost pressure to the atmosphere
• Compressor Bypass: Does not vent to atmosphere. Reroutes all boost back to the low pressure side of the turbo
• Hybrid Valve: Will vent a certain ratio of the compressed charge to the atmosphere, and reroute the remaining to the low pressure side of the turbo

The factory blow-off valve is computer controlled, made of plastic, and comes with a low pressure spring. The light OEM spring and computer controlled valve bleed boost, both for emissions testing and to protect the engine from high boost. When you decide to add more boost to your EcoBoost or just want to know if all of your boost is making it to the engine, upgrading the blow-off valve is a good way to do that. Aftermarket blow-off valves are mechanically controlled via vacuum, so they are able to actuate more reliably than the OEM valve. When you are in boost, the vacuum reference line keeps the blow-off closed. Once you step off the throttle and the engine goes into vacuum, the pressure differential between the manifold and intake blow-off valve force the valve open, releasing boost pressure and protecting your turbo. 

• Reduce turbo wear due to compressor surge
• Prevent bleeding boost
• Relies directly on boost or engine vacuum, no computer controls

Once you have a blow-off valve installed on your EcoBoost Mustang, you’ll notice more stable boost pressures, less bleeding of boost, and you will typically see quicker spool times as a result. A properly installed and set up valve will also keep your turbo bearings and shaft from being damaged by compressor surge. You can’t go wrong with an upgraded valve from stock!