R18 to R20

I may be a little late on this, but I think that it's better to turbo charge the r18 vs the r20. Turbo chargers increase oil compression and so does vtec. Turbo charging an si makes it harder to use the full potential of vtec and the turbo charger and you have crazy oil compression, which will cause the engine to blow. While the r18 doesn't have vtec, you can have higher psi and take full advantage of turbo. But as you said earlier, replacing certain parts of the engine with r20 parts, I believe its doable, if you know what you're doing.

Okay, first off, I own a 07 Civic Si. I never said the r18 is stronger than the Si, I only said that turbo is more suitable for the r18.

Supercharging the r20, in my opinion, is a much better option for the si, only because it can only handle so much psi ( again, due to vtec). You'll blow your engine if you have too much pressure with turbo ( and also superchargers, but it's much safer with superchargers).

There's a reason why evos and imprezas can handle 20+ psi and our engines can't. Do not get me wrong, I love my car and engine in every way, but I am no bias to only my 07 Civic Si sedan.

I have spent a year debating on whether I should go turbo or sc, so don't think that I haven't done research on this. Turbo is doable on a r20, yes, I have never denied that.