1.6 liters
the VE is good at the low end rpms, on this motor (you not going to help it there)
so where do need this power, at 5000 rpm?
and if yes, then you can move that low end power to the upper end with radical CAM and custom tuned exhaust.
tell us , exactly what you are trying do , RPM wise.?
at what speeds, , racing, off road. or what?
that 1.6L (naturally aspirated) is very limited by its very displacement, and is fully developed for good power with the 1.6L 16v head.
so where do you want that power and are you willing to loose low end power.
i know every header maker and exh maker all promise, fast,easy , pure power. but most lie.
Ask them for dyno proof or track times.