From Stock WRX to Daily-Driven Track Terror – Part One

By: Chris Neprasch

Our latest mission is to turn a stock 2004 Subaru WRX into a car that can handle its own during local track days and on the autocross course while still maintaining enough civility to be a reliable daily driver. This means no huge turbo setup that is useless below 5,000 rpm, no super soft compound race tires or anything else that would affect important creatures of comfort like AC.

We aren’t going to be getting too crazy with the WRX. The main purpose isn’t to build the fastest car at the track; our pockets aren’t that deep. It’s also not going to follow the guidelines for a specific class because we want to do things our way and not be limited by certain rules. We’ll see what it fits into when it’s done. What we are going to do is build an affordable, well-balanced car that will be a blast to drive on the track and fun to cruise around the streets. It will look fast, be able to back it up and everything we bolt on to it will be because it’s functional and isn’t going to break the bank in the process.

One thing most owners of turbocharged vehicles eventually do is installing a blowoff valve. The factory Subaru blowoff valve is one of the better ones we have seen from OEMs. The construction and materials used are solid, but we’re installing the Blitz Dual-Drive blowoff valve because it is adjustable, offers a tight seal to prevent any boost leakage and will be put to good use with the future planned upgrades. That and we don’t mind that everybody at the track will know when we’re shifting gears. It also flows 20 percent more air than their previous design and has a small port for low boost as well as a large one for high boost. It is built to handle 18 psi and can tolerate more with an upgraded spring kit.


The first step to installing the Blitz unit is removing the three bolts that hold the hard vacuum line to the top-mount intercooler. Once the bolts are removed the vacuum hose that connects to the hard line at each end can be pulled off. The hard line can now be easily removed from the engine compartment and set safely aside for now.

There is a vacuum hose on the top of the factory blowoff valve that needs to be pulled off. After the hose is disconnected there are two bolts that hold the Subaru blowoff valve to the intercooler that need to be removed. When the bolts are out there is a clamp that holds on a large vacuum hose to the bottom of the blowoff valve. When the clamp is opened the blowoff valve can be pulled lose and removed from the car. Be careful not to damage the gasket since it will need to be reused.


The Blitz unit we chose is a direct-fit application. The body is separate from the flange, but Blitz supplies both along with a gasket to prevent air leakage. Two bolts are also included to mount the body to the WRX-specific flange.

There are two options to choose from to determine how the air is vented from the Blitz blowoff valve. The first (pictured above on the right) attaches a SUS filter at the end of the valve which is quieter than the completely open design. Don’t put either on yet because it will block access to the bolt hole on one side of the flange.

The factory blowoff valve circulates excess pressure back into the system while the Blitz piece vents it into the atmosphere. Blitz supplies a plug to block off the large vacuum hose that originally connected to the bottom of the factory blowoff valve. Install the plug and reuse the factory clamp to hold it in place.


Use the two supplied bolts to mount the blowoff valve to the intercooler. Once it’s secure then slide the included hose clamp over the smaller vacuum hose then on to the Blitz unit. When the flange bolts are torqued down then install either the SUS filter or the open fitting.

The reason why the hard vacuum line was removed at the beginning is because it needs to be modified to provide clearance for the larger Blitz blowoff valve. The opening on the hole nearest to the driver’s side of the car needs to be enlarged about a quarter of an inch on the bottom with a file. Reinstall the hard line with the three bolts and reattach the vacuum hoses on each end. Start the car, double check to make sure nothing is leaking and minus some small adjusting the job is done. Be sure to check back next Friday as the series continues because there is a lot more planned for this little WRX.


Blitz North America
Address: 18050 Newhope St.
Fountain Valley, California, 92708
Phone: (714)-515-4001

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