Is the difference between these two engines purely the throttle body at a guess? Am assuming the Twinport engine has a TB with a second intake port for when you're 'giving it some'?
There's 15bhp OEM difference between the two engines, what's the odds of (if the engines are similar) fitting the Twinport TB and perhaps intake manifold to the Z16XE? Would it let you access these extra little ponies?
Or am I guessing completely wrong and I need a good slap for being silly?