Originally Posted by Kingtal0n

And because you are so specific, I will be also

For math involving rough horsepower estimates, use these rough equations:
(CID * RPM / 3456) = CFM
CFM * .069 = lb/min airflow

So, for an SR20DE engine,
(122 * 7000 / 3456) = 247CFM
247 * .069 = 17 lb/min (170 horsepower)

that equation simply says that an OEM sr20de engine with 100% volumetric efficiency should produce 170 horsepower at the flywheel on a BAD DAY. Since .069 takes into account the air temp rise of a turbocharger, this estimate is LOW. But since we are neglecting the fact that an OEM sr20de engine is not at 100% VE around 7,000rpm we are actually HIGH in our estimate. That is why this equation is very ROUGH.

So lets turn up the boost some, SR20DET engine @ 14.5PSI:
(122 * 7000 / 3456) = 247CFM * 2 (double the atmosphere) = 494CFM
494 * .069 = 34lb/min (340 horsepower at the flywheel)
Now subtract drivetrain loss, about 13%, (340 * .87) = 295 RW Horsepower.

Most SR20DET engines with sufficient compressor flow will product approx 300 RWHP at 15psi so this is very accurate estimate.

Notice if we bump displacement slightly (due to overbore) there barely any increase to the overall flow capacity of the engine. If you want a larger displacement then you need a bigger engine, dont expect an overbore to give you back any spectacular results.