The 4A black top version will come out the door with more power, but it also has a compression ratio of 11:1 vs a 9.4:1 or 10.3:1 depending on what generation of 16v you're going with.
I'd probably stick to a 16v since it's much easier to mod, plus if you wanted to lower the compression a bit to play safer with forced induction you can do so by putting a thicker metal head gasket on it, and HKS still has those in stock. The biggest problem I'd find with a 20v black top is that the motor itself is mostly seen in Japan, and if you're looking to modify that motor your best bet is to know some Japanese. While there still is support for older motors in Japan, there isn't as much as there used to be as everyone has been moving onto newer/better things.
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