.48/.60 IS too big for street use for a 1.6L-1.8L engine, regardless of what you may have been told, a .42/.48 would be much better sized for your engine, providing much better response, as far as getting 20psi...no a t25 will not produce 20psi...but you yourself said this is for street driving...15psi is easily attainable on it, good throttle response...as far as centrufigal superchargers, it takes time to build RPM just as much as it does to build load, unless your launching at 5k RPMs and staying above that the whole time you will have lag with a centrufigal sc anyway, if you look at the cars they used .48/.60 turbos on stock you'll notice one thing...they are all larger than 2.0L, why? they didnt want turbo lag, I personally drive in the 4k-6k RPM range most of the time when driving agressively...therefore...no turbo lag, if I'm out of that range I do a little thing called downshifting....bam, instant boost