STi2EvoX

Going with a thicker viscosity shouldn't have anything to do with displacement, it's more based on how the motor is designed and how much hp the car is making. With masive power levels comes massive cylinder pressures and this the need for a thicker oil to provide adaquete protection. I'm guessing that with your 2.3 L stroker kit that you are running a big turbo? Perhaps that's why your mechanic recommended the thicker oil. Even still, a 30 viscosity oil is still suitable for very high hp levels.