Generating turbo power is about more than hard parts. "The fuel system had to be reengineered, making it a return system," adds Stevens. "To make things worse, the lay out of the fuel tank is like a saddle tank, so fuel had to be transferred from the passenger side to the driver side via a jet valve."
Stevens says this jet valve works with the regulated pressure passing through an orifice to create a vacuum. "The vacuum side is connected to the passenger side of the fuel tank and sucks fuel over to the driver's side where the fuel pump is located."
"There is a problem associated with this decision," says Stevens. The jet valve is too restrictive. "We had to make calculations to modify the jet valve based on the amount of fuel we were returning at idle, part, and full throttle. We were able to get it just right, and attain a balance between both sides, which eliminated any chance of long-term fuel level problems."
"We were also able to increase the return flow, so we could maintain precise fuel rail pressure, which was crucial with the IS300," adds Stevens. "The injector duty cycle cannot be altered directly because doing so makes the ECU's logic think the engine is misfiring. Therefore a consistent pressure is critical. A lack of consistency results in a surge at idle and hiccups during initial throttle."
To increase flow volume, a Walbro high-flow, high-pressure pump, Aeromotive regulator and a Cartech billet FMU were installed. The car was ready for test runs and Stevens experimented with different line pressures in the transmission until he attained good response and proper shifting.
Engine tuning is executed with a TBKO piggyback ECU computer while a TBKO shift computer keeps the gears changing. With a few road trips under its belt, the IS300 was scheduled for a dyno tuning session. After only a few fine tuning runs, the 2JZ-GE pumped out 321 whp and 300 lb-ft of torque at 7 psi. Our own long-term IS300 laid 174.6 whp in stock trim, so Stevens is up 147 hp at the wheels. It should be noted that the engine runs a factory bottom-end and the stock 10.5:1 compression.
At this point in the car's evolution, the suspension had some catching-up to do. Yuen wanted to maximize the sporty suspension Lexus delivered from the factory so he elected to go with coil-overs. The weapon of choice was Tein's CS system.
The CS or Comfort Spec system featured ride adjustable coil-overs with 448 lb-in. springs in front and 336 lb-in. springs in the rear. The system uses rubber upper mounts but pillow ball mounts are available as an option.
Bracing can give a vehicle extra stability that makes all the difference on the road. In the realm of VIP-style sedans, bracing is more critical because the cars are usually bigger, heavier and much more commuting oriented than traditional sports cars. Yuen fortified the chassis of his IS300 with a Do Luck rear cross member bar, Cusco triangle brace and Cusco front and rear strut tower bars. Yuen has taken his lust for J-spec gear and opened SKR Performance, a comapny that imports exotic JDM stuff to the U.S.
There's no doubt Yuen is living large in his VIP-inspired IS300. However, large does not always mean satisfied. Yuen has some more tricks up his sleeve including a move from the current TBKO Stage I kit to Stage II status. That's the thing about fevers: Just when you think it's all under control, there's a flare up.