Written By: Mark Modaressi

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Now that we’ve installed some of the “basic necessities” (Please read Project Evo: The Basics – Gauges we decided to make sure we wouldn’t experience any boost issues in the future by upgrading the stock bypass valve on the Evo for a better quality aftermarket unit.

You’ve probably heard lots of talk about blow off valves and the “pshhhhhhh” sound as a reason for getting one, but in reality there’s a much better reason to do so for the Evo.  It turns out the stock bypass valve on the Evo is identical to the plastic unit found on the G2 DSM models.  This bypass valve has a tendency to leak because of it’s poor quality and that can cost a few pounds of boost on the Evo, especially once modifications are made and boost goes up.

We decided to replace the stock bypass valve with a unit from Forge Motorsport, USA. Forge Motorsport offer two types of valves depending on what you’d like and you’re requirements. One is a vent-to-atmosphere (VTA) blow off valve and the other is a recirculating blow off valve. Forge blow off valves use counter balanced springs and dual pistons to prevent them from leaking air into the intake system at idle.

Forge blow off valves have the ability to swap out the spring to adjust the tension on the valve.  All valves ship with the softest spring (green), but a blue spring (medium), and red spring (stiffest spring) are also available if you up the boost and find the need to upgrade. All you have to do is unscrew the top half of the valve using an allen wrench and then replace the spring with the new one.

VTA blow off valves do just that, vent the excess air right to the atmosphere.  A recirculating blow off valve will actually recirculate that excess air back into the intake. This is actually a quieter method and there’s a good reason to do this on vehicles fitted with a Mass Airflow Sensor (MAS), like the Evo.  When driving the MAS will read in a specific amount of air coming in to the intake and wants to compensate for that  air with a certain amount of fuel. If you use a VTA blow off valve then that air will no longer be entering the engine, but the fuel is still compensating for it, so you end up running too rich.  This has apparently caused stalling problems for some people. A recirculating blow off valve will work just like the stock unit, so there shouldn’t be any potential for stalling issues.

Since there was a lot of talk about both types of blow off valves on the site, we decided to install both the Forge VTA and recirculating blow off valves on our Project Evo and test them out for a few days so we could see what each was like and report our findings.

Tools Required:

• 3/8″ or 1/8″ ratchet with 10mm socket.
• Phillips head screwdriver
• Pliers

Removing the stock bypass valve is a very simple process:

1. The stock bypass valve is located just next to the intake. To make things easier, remove the ram air piece from the intake so you have more room to work with.  This involves popping 2 small tabs located in the front. Make sure to push those tabs in to loosen them, don’t try and pull up on them or they will probably break.

   

2. Once the tabs are out, you can remove the ram air piece from the intake. Notice the black piece next to the coolant hose and intercooler piping?  That’s the stock bypass valve we’ll be removing.
3. Now we want to remove the stock bypass valve. There are 3 clamps to loosen in order to accomplish this. Using the small 1/8″ or 3/8″ ratchet and a 10mm socket, loosen the first clamp like so:
   



4. Now remove the second clamp up top.  You can either use a phillips head screwdriver or the same ratchet, depending on your preference:
   



5. Now pull the bypass valve out so that you have more room to work with it to remove the final hose.  Now that you have more room, take a pair of pliers and move the clamp out of the way so you can remove the final hose:
   

Now you’ve completely removed the stock bypass valve.

To install the Forge VTA blow off valve, follow the steps below:

Tools Required:

• 3/8″ or 1/8″ ratchet with 10mm socket.
• Phillips head screwdriver
• Pliers

To install the Forge VTA blow off valve, follow the steps below:

1. First use the special plug that comes with the Forge kit to block the opening back into the intake tract. Now tighten the clamp down using a ratchet.
   



2. Now insert the small hose onto the Forge VTA blow off valve.  Use the pliers to slide the fastener clip over the hose to secure it in place.
   



3. Next, insert the Forge VTA blow off valve where the stock bypass valve originally was.  Now tighten the clamp down using a ratchet or a phillips head screwdriver, whichever is easier.
   



4. That’s it! Now that the the blow off valve is installed, take the car out for a test drive and see how it runs.

To install the Forge recirculating blow off valve, follow the steps below:

Tools Required:

• 3/8″ or 1/8″ ratchet with 10mm socket.
• Phillips head screwdriver
• Pliers

1. Insert the small hose onto the Forge recirculating blow off valve.  Use the pliers to slide the fastener clip over the hose to secure it in place.
2. Now, insert the Forge valve in place of the stock unit. There is some debate as to which end goes in which section. Our own experience led us to follow the same positioning as the stock BOV. When we installed the valve in the opposite orientation, we experienced a strange sqeaking sound from the valve. Forge Motorsport mentioned that either way can work and comes down to personal preference. We recommend trying both orientations to see which works best. Once securely in place, tighten the fasteners using a socket wrench and/or phillips head screwdriver.  We noticed the stock vacuum hose can get pinched, so we recommend purchasing a longer tube from a local hardware store and replacing the stock piece to prevent any potential issues that may arise.

That’s it! You’ve now got a recircualting BOV that shouldn’t cause boost leaks and maintains a very stock like look

Sound Clips: All sound clips were conducted inside the car with the windows up to give an accurate idea of what the sound would be like.

Reviews:

Reviews
Forge VTA BOV	We experienced very few issues when running the Forge VTA BOV.  We were expecting heavy idle issues, etc, but this was barely present. We did still find some issues when coming off the throttle abrubtly. This would send the rpms skyrocketing down below idle and almost caused the car to stall. The sound from the BOV was very clear with a nice whoosh sound once boost was built up and released. Building up boost and lifting off next to a vehicle or pedestrian definitely got heads turning and occasionally a few people jumped In the end, we believe some idle and  drivability characteristics will be sacrificed in order to get that loud “whoosh” sound.
Forge Recirculating BOV	The Forge Recirculating Blow Off Valve is a great replacement for the stock BOV if you are experiencing leaks, etc. There is a little but more of a whoosh sound then before, but it’s very hard to head unless the windows are down and you really build up some boost. Unlike the VTA version, we did not experience any idle or drivability issues with this BOV. If you are looking for a louder whoosh sound, you can purchase an open element intake system to increase sound, but with the stock airbox in place, it just won’t come close to the VTA version.

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