Subiesport Magazine - April/May 2008 - (Page 45)

TUNING THE 2008 STI room in the wheel wells. Previous stock Subarus maxed out at 8.0 inches (without fender modifications), but the new 2008 STI comes with 55 offset 18x8.5-inch rims. For those who autocross in stock classes, this allows a great selection of wide rubber. Suspension parts are just now coming to market for the 2008, but a set of H&R lowering springs were acquired and fitted, as well as a set of JIC Magic 9.5-inch wide, 45 offset 18-inch wheels shod in 275/35R18 BFG KDW2 rubber. To help pull in some of the factory understeer, a Perrin 19mm rear sway bay was installed in favor of the stock 17mm bar. The addition of the Perrin Positive Steering Response System (PSRS) added three degrees of front caster (totaling to 6.8 degrees!), while the Perrin subframe brace tightened up the lower control arms. Interior Instead of going the usual tuner route of having five or six of the most critical gauges, Jeff decided to go with the latest technology from PLX Devices — a pair of beautiful 60mm OLED full color gauges that can read from a variety of sensors — installed within a Perrin Gauge Pod. Since the 2008 STI has A-pillar airbags, you can’t add a pillar-mount gauge pod, so the two-gauge approach maximizes the return on real estate. For sensors, Jeff chose the PLX AFR, boost, oil temperature, water temperature, air temperature, and oil pressure data collectors. These sensors then feed the PLX brain box with data that can be shown on the two color displays. With the touch of a single remote any parameter can be seen or recorded. The further addition of the PLX iMFD Datalogger allows complete data collection with offline viewing via your laptop. Since all the sensor modules daisy-chain, you can add more sensors as needed without more gauge clutter. The clarity of the PLX gauges is uncanny, and it is clear that this kind of display is the wave of the future. Three turbos all in a row (L-R): Stock 2008 WRX TD04, Stock 2008 STI VF48 and a Garrett GT3076R “GT30R” turbo upgrade. The latter is good for up to 400 wheel-horse power PHOTO: TRAVIS GENY MODIFYING THE AVCS TO ELIMINATE LAG LAG. DESPITE ONLY containing three letters, it really is a four-letter word in the world of turbocharged engine tuning. Lag is basically the time delay from when you hit the loud pedal to when the turbocharger begins making useable boost. Lag is not a fixed time delay; how much lag a given car has depends on a few variables, like displacement of the engine, size of the turbo and even the cam timing. While the first two variables tend to be fixed, Subaru has developed a system to vary cam timing, known as Active Valve Control System, or AVCS. But first we need a quick primer on how a cam works. Basically, a cam is a rod with bumps on it. As the cam rotates, the bumps, or cam profiles, act on the valves in your engine to open and close them. Normally, the order in which the valves open and close, also known as cam timing, is fixed. The timing belt rotates the cam, which spins and opens and closes the valves as determined by the position of the cam lobes on the cam shaft. This system works very well, but it presents the tuner with an absolutely fixed variable in cam timing. AVCS changes this. AVCS allows the cam shaft to advance or retard cam timing, on the fly. It does this through a series of oil pressure switches and solenoids. Essentially, instead of rotating around a fixed axis, the cam lobes can be made to open valves earlier or later in the combustion cycle. But why would we want to do this? The simple reason is that your cams determine where your engine makes power. They determine where and when the valves open to let fuel and air in, and exhaust gasses out. In a turbocharged car, power is made when exhaust gasses spin a SUBIESPORT MAGAZINE 45

Table of Contents Feed for the Digital Edition of Subiesport Magazine - April/May 2008

Subiesport Magazine - April/May 2008 Contents Travis Geny Letters Readers' Rides Subaru News Wicked in White Pink Rules Harman Motive Nouveau Tuning the 2008 STI 2008 Rally Guide Alcan 5000 Rally Alcan Unleashed WRC Rally Monte Carlo WRC Rally Sweden WRC Rally Mexico 100 Acre Wood Kumakubo! D1 Drifting Where to Buy Subiesport 2008 Impreza WRX 2007 Legacy GT 1993 Impreza Wagon Fueled Up Ad Directory Spotted!

Subiesport Magazine - April/May 2008

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