Nerd's Eye View- Inside Evasive Motorsports Scion FR-S!
by Mike Kojima
You have probably seen photo spreads of this car in Speedhunters and the magazines. You might have ogled it at the SEMA show. In our opinion the Evasive Motorsports Scion FR-S is the most beautiful FR-S built so far. It's mean looking bodywork looks like it was taken right from a JGTC GT300 car. Although the car, like so many other FR-S projects rushed to completion for last year's SEMA show, certainly looks the part, many of you might dismiss it as being simply a show car.
Well the Evasive FR-S is much more than that. It is fast. It is currently the fastest FR-S around Buttonwillow configuration 13 and has competed at Pikes Peak. This spring we were lucky enough to get to work on the Evasive car while helping to develop its chassis set up. This enabled us to get a look at the side of the car no other publication has touched on from an insider's view.
If you are curious to see just what is inside the car beyond the pretty pictures you have probably already seen, read on!
The Scion's F20B engine has been rebuilt and fortified with HKS forged pistons with an 11.5:1 compression ratio. This is lower than the stock 12.5:1 compression and more suitable for forced induction. The compression ratio is a little higher than the factory turbo variants of the motor found in the Japanese Legacy. Legacy turbo connecting rods are used as well. The factory rods were retained because of the F20's odd offset bolt design which facilitates tightening in a flat motor. At the time the engine was built, there were no rods like this on the market. The heads are sealed with HKS MLS head gaskets. Cusco chassis bracing stiffens the forward part of the chassis.
A modified HKS supercharger kit is used to provide boost to the engine. The unique thing about the HKS supercharger is the traction drive transmission. Traction drive use smooth toothless steel rollers with a special traction oil to transmit drive force from the crank driven pulley to the compressor shaft. The first most notable advantage of the traction drive is that it is practically silent. The second advantage is that a traction drive has less parasitic power loss than gears or belts and pulleys. The final cool feature is that you can have a higher gear ratio to spin the compressor up faster for less lag while the traction drive will still allow for some engineered slip to take place before the compressor wheel overspeeds or goes into surge at high RPM's. This gives the HKS supercharger a wider operational range than what is typical for a centrifugal supercharger.
A large HKS Blow off valve functions as a part throttle bypass valve. This reduces the supercharger's drag at part throttle. Cusco hard motor mounts help keep engine movement at bay.
Evasive modified the kit with larger charge pipe plumbing and this large HKS EVO X intercooler as well. A smaller supercharger pulley increases the boost over the standard kit. The engine is tuned with ECUTek software. In its current level of development the engine produces 405 hp to the wheels. Not bad considering the current very mild level of tune.