Simple is better in this case, so we selected a GReddy PRofec-B. The PRofec B was selected because of its ability to not only control boost easily from the driver's seat, but to improve throttle response and to reduce turbo lag as well. A properly set up electronic boost control can do this because it can pinch off the air reference signal to the wastegate with a duty cycle stepper motor valve.
When the driver's set boost level is reached, the boost controller will send all of the pressure signal to the wastegate, blowing it open quickly. Normally, when the wastegate boost reference line is merely attached to the manifold, the wastegate opens slowly, well before the set boost point to prevent boost overshoot or overboosting. Overshoot is prevented, but because the wastegate valve is opening slowly before the actual set point, boost builds more slowly as well. Manual bleed type valves like the infamous aquarium valve can raise the boost level but also make boost response sluggish for the same reasons.
The PRofec also can be set to control the boost control pressure to both sides of an external wastegate's diaphragm. This allows the use of a lightweight spring in the wastegate, allowing a large latitude of boost adjustment. We have a 6-psi spring in our wastegate, but due to the PRofec's ability to put control pressure to both sides of the diaphragm, we can adjust our boost from 6 psi all the way to 22 psi from the cockpit. The PRofec-B also has the unique feature of being able to adjust its response speed to the wastegate's response time. This feature allows the user to tune the Profec for maximum boost response speed without boost overshoot. Because the Turbonetics Racegate is a responsive external wastegate with a big poppet valve, we set the PRofec for its quickest response level for the most aggressive possible boost curve.
The PRofec-B also has a cool remote trigger feature. This is a radio frequency controller you can attach to your steering wheel for easy reach and allows you to remotely toggle between high and low boost. This is very handy with a high-powered FWD car; you can launch at low boost and when in higher gears, easily switch to high boost at the touch of a handy button. With the radio frequency controller, there are no complicated wires to install. Just strap it on and it's ready to go.
To monitor the boost pressure, we installed a JWT boost gauge using the gauge pod for a Twin Turbo Z. Surprisingly, the pod almost fit. We heated it with a heat gun to soften the plastic slightly so we could mold it into shape to fit our Sentra a little better. The JWT gauge can read up to 30 psi, which is more than we ever anticipate running.
California's new 91-octane gas is bad news for turbo lovers. The 91-octane fuel is like light beer, and turbos don't seem to like it much. With the poor quality gas, most of us in this state have had to lower our boost pressures by several pounds or retune our engine management systems to tolerate the fuel at the cost of much lower performance.
To help us with our fuel dilemma, especially since we are running a higher compression stock engine, we looked for new ways to suppress detonation without compromise.
Our savior in this case was an Aquamist competition water injection system. Aquamist water injection systems have been used in FIA rally cars for years, enabling lots of boost pressure and advanced spark with reliability.
The Aquamist system uses a sophisticated solid-state piston-type pump that pumps the water at 130 psi. At this high pressure, there is little likelihood boost pressure can reduce water flow significantly, a problem that plagues other water injection systems which only run a typical 10 to 20 psi. If you only have a 10 psi water pump and are running 15 psi of boost pressure, the resulting positive pressure differential ensures you won't get much water out of the system!