APS High Volume Twin Vent

Blow Off Valve

 

The Subaru Impreza WRX has unique blow off valve requirements particularly when fitted with a large turbocharger. A blow off valve is a device that releases pressure from the turbocharger when the throttle is released. APS designed the APS high volume twin vent blow off valve specifically for the Subaru Impreza WRX. It is an ideal enhancement for applications using the standard turbocharger up to a large 600 hp units.

With its huge capacity the APS blow off valve gives you the ultimate in turbocharger durability and improved turbo response particularly during gear changes. A mammoth 34mm internal bore size delivers huge capacity and at full piston travel, all ports are fully exposed for maximum blow off volume. The large primary vent is designed to plumb back to the standard entry point which ensures the best driveability during cruise conditions and cures the problems seen with after market external single venting blow off valves.

 

And for large turbochargers running high boost pressure levels, the APS twin vent blow off valve continues to vent through to the second stage port. Fine adjustment to blow off valve operation can be performed through the actuation adjustment screw for optimum configuration. It's what we use on our 540hp WRX race car.

 

MY99 - MY00 BOV System shown above - includes every component required for installation.

 

APS BOV development: APS are often asked why they developed their own blow off valve when there are so many on the market. The reason is they have not found a blow off valve for the WRX that offered the level of performance required. With a large turbocharger, releasing pressure from the turbine compressor wheel when the throttle is snapped shut is critical not only for turbocharger response, but for turbocharger longevity. A huge volume of air must be passed through the blow off valve as soon as the throttle is closed. Most blow off valves have limitations in their design that inhibit the level of performance we demand. Piston/bore diameter and venting ports are often too small and surprisingly, most will not fully expose the exhaust ports when fully opened. Ultimately, the need for a truly high performance blow off valve specifically designed for the WRX needed to be satisfied. The pictures below show various aspects of blow off valve design and compare particular features of the APS dual vent blow off valve with other respected blow off valves(s).

Air entry into the blow off valve

APS BOV on left - Other on right

APS BOV entry port is over 30% larger

 

Air entry into APS BOV 30mm with 32mm internal bore diameter Area 707 mm2 opening with 804 mm2 bore 30% larger port and 21% larger bore	Other BOV 26.3mm entry and 29mm internal bore diameter Area 543 mm2 opening with 660 mm2 bore
Primary vent port (plumb back port) This port vents the majority of air back into the standard return line APS BOV on left - Other on right APS BOV entry port is over 42% larger
APS BOV 30.2 mm primary vent port bore diameter Area 716 mm2 port size 42% larger port	Other BOV 25.3 mm primary vent port bore diameter Area 502 mm2 port size
Piston travel in the APS blow off valve fully opens the primary venting port. This means the entire port is open to quickly vent excess pressure	Other blow off valve cannot fully open the primary port. The piston reaches its travel limit well before the port is fully open.

Piston travel in the APS blow off valve fully opens the secondary venting port. This means the entire port is open to quickly vent excess pressure.		Other blow off valve cannot fully open the primary port. The piston reaches its travel limit well before the port is fully open.
Another example of a blow off valve that looks similar to the APS blow off valve. Unlike the APS BOV, this example's piston reaches its travel limit well before the port is fully open.		Another example of a blow off valve that looks similar to the APS blow off valve. Unlike the APS BOV, this example's piston reaches its travel limit well before the secondary port is fully open.