Porting WRX TGVs at Home

An American Thing
Subaru doesn't use the TGVs in Japan or European WRXs (and the USDM '05 STi won't have them either, controlling off-throttle airflow with its electronic throttle-body), but as our American-spec CPU expected to see TGV butterflap motor operation and register response from the angle sensor on the opposite end of the actuator, we couldn't swap in the offshore risers everyone else gets to use. Also available were the APS TGV Eliminators, nifty cast aluminum units that install in place of the stock TGVs, but have nothing of the butterflap sort within them. That kit also comes with a neato bit of billet that bridges the OEM sensors to fake the computer into seeing nothing amiss, and a second set of ports for you auxiliary-injector types, but it's a $600 that we'd rather spend on beer. Preferably expensive Stone Brewing products we'd drink AFTER grinding the sillies out of our TGVs.


Instead, we did the used-part dance and came up with a set of TGVs from an '04 WRX STi attached to a host of other STi parts, priced to move at $150. After parting the whole conglomeration we were $150 in the black and still had the TGVs, STi charge tube, wiring harness, fuel rails (should've kept those injectors) and electronic throttle body. Anyone want the throttle body? Stupid electronic throttle-body—cable-drive or die.


You can save yourself a good deal of consternation by experimenting on spare parts. We could have pulled our stock TGVs, done a rush job and ported them in a hurry, so we could put the car back together. We're not big fans of stress, though, so we planned instead to slowly dissect our spare pair and do the job right. As self-doubt is the malaise of all by-the-gut wrenchers, we wanted confirmation of what seemed a relatively Stone Age idea. Our buddy Beto Campa is a high school teacher by day and hi-po domestic race-head builder in the off-hours (Maximum Power Technologies, maxpowertechnologies.com), and a friend of the house. We figured if his considerable porting instinct were available to underwrite our theories, we'd feel all sorts of better about taking a hatchet to things.

Clean 'Em Out
Stopping by his home on Saturday with the TGVs in hand, we anted up the going rate for advice (one bottle of tequila, with worm) and gave him a look-see. It took but seven seconds (perhaps not that) for Beto to size things up in the TGVs and deem their layout "silly." "Clean 'em out." He suggested we also make sure the TGV-to-head transition was smooth. When confronted with sensor placement on the TGVs, Beto figured that after we remove the butterflap we could leave the pivot shaft, grinding it down for reduced profile at W.O.T. Beto also told us the USDM 2.0-liter upper manifold was not worth porting (we'd brought one with us), and knife-edging and flowing the cable-driven (Yay!) throttle body would yield minimalist flow gains at best (we're going to anyway). OK, TGV all-go.

Butterflapectomy
We first had to grind off a set of pressed-in fittings—Phillips-style screw heads that had been fixed at the factory so as not to back out—that secured the butterflaps to their pivot shaft. Not much of a process; we selected a little piece of scrap wood to hold the flaps open against motor tension and went to work. With the pressed portion of the machine screw gone, backing the other end out of the shaft and TGV flapper was much easier. We'd used a Dremel motor tool with a tungsten steel bit (worth every penny) and, while it was perfect for close-in work, the immediate fear we tripped into was that the short, high-RPM bits would not properly reach into the narrow TGV opening. With the butterflaps out, this was now obvious. Not good.