Porting WRX TGVs at Home

It's old-fashioned tuning, hammer and chisel stuff akin to hacking off the mufflers and running around uncorked for every horse it could provide. It's new tech, counting on the computer to accommodate the details of modded hardware and not seeing the subterfuge of emissions alterations and missing parts. It's trial and error, chasing one part with another and another to keep ahead of the OEM's prescription.

The Nonsensical
The Subaru WRX, for all its beautiful freakish offshore performance and night stalker sleeper demeanor, is not without its flaws. There are suspension bits that weren't thought out, the transmission and clutch package is an obsolete bandage Subaru hoped would last until the STi six-speed was available, body panels are so thin you'd better dodge the big bugs, and there are a few concessions in the engine to help the dirty little flat-four pass stringent American smog standards. Those emissions requirements were actually the principal reason the turbo'd WRX didn't show up years earlier, and Subaru had to commit to dramatic changes to make the car U.S.-legal—changes which flew in the face of performance sense.


So as you spend time poking around within the engine bay of your WRX installing go-fasts and zip-tying blasted undertray parts to each other, you begin to notice those nonsensical items. Give it a few months and they begin to gnaw at you; so, depending upon your hands-on wrenching competence, it's possible you'll wind up yanking off parts and grinding the noodles out of 'em at midnight just like us.


Speaking of flying in the face of performance, here's a part with wings for cross-sense purpose: tumble generator valves, the TGVs. With the exception of the catalytic converter Subaru parked within the exhaust manifold IN FRONT OF the turbocharger (the things we do for emissions; what about the harm done to mileage and efficiency—), the TGVs are likely the single most performance-detrimental part on the engine.


It's not a complicated effort to divine the function of the TGVs. One large butterfly valve in each intake stack just prior to the heads (four total) flaps shut at partial and no-throttle operation to force the intake charge (coming off the turbocharger, already chilled by the factory aftercooler and moving at high speed) to divert into a narrow inlet to compress the air and induce a leaner mixture and promote a cleaner burn. OK in theory (well, not even then), but not only does that butterfly flap (a butterflap!) not open completely at wide open throttle, but the pivot shaft and diversion channel wall still sit there obstructing flow. You need to fix that.