.02---
The 335 is an inch and a half longer. I do have to wonder if the stock throttle body will become a restriction when trying to chase 500hp. With the turbos, you are forcing air through it. With a draw-through blower, it acts more like a throttlebody. You would have 500hp worth of air trying to be inhaled through it instead of shoved through it.
To touch on Mines13's good point---my Goal is 15psi or simply one atmosphere of pressure. With 7.5psi, you are adding 1/2 the displacement worth of air (The "box 6 feeling" that has been associated with the Sprintex.) With 14psi, you are doubling the airflow of the existing engine. That would feel like a "Boxer 8", basically. 21psi would be a "Boxer 10". 29psi would be a "Boxer 12".
Goals are important. The versatility among the boosted options are a healthy thing. These are like different masks or characters for the same car
.
A "hit" of power or "yank" (torque)---Roots, twin screw, n/a--good for autocross or tight road course, drift (IMO...).
A "rush" of power, or "horsepower"---Turbo, centrifugal, nitrous---good for drag, standing mile, fast road course.
14psi making 400hp or thereabouts would tickle my fancy. I don't know if the valve springs could do it, though. These are supposedly weaker than the WRX. Anyone know for sure?