Technical Differences Between Opel 1.6 and 1.8

I've been thinking about this lately given how similar these engines are from what I have gathered so far and I wanted to see what people may know on here.

GM tends to run similar designs in terms of engines I've noticed, take the 3100 and 3400 series V6. The 3100 makes 160hp and 180tq and the 3400 makes 180hp and 200tq. Now these basically are the same engine minus the displacement and a few key points. Those key points are the better flowing heads, intake manifolds and a slightly larger throttle body. GM in 2000 decided/discovered that if you put those better parts on a 3100 you can bump the power to 175hp and 195tq. So you can basically do a top swap to add 15hp and 15tq.

So my question is why is there roughly a 28hp and 18tq gap between two very similar engines as far as I have read? Or is there something different mechanically I have missed? Or is it tuning. Any thoughts?

I apologize, in advance, for creating a zombie.

They must have all different blocks, crankshafts, pistons, etc. All of the lower parts would have to be different because the 1.6 cannot be bored or stroked to those dimensions safely.
If you look at the engine of the Chevy Cruze 1.6, it is the exact same engine as in the Aveo, but has nearly 10 HP more output. The only difference that is visually noticeable is the airbox assembly.

It has to be the tuning, in combination with less restriction in the intake system. Most likely for emissions reduction for the American market. The 1.8 is producing more power per liter of displacement than the 1.6 , it would have to come from that.

the cruze is the 1.8?

the 1.4 -1.8 use the same block from my research. in both generations.

if a 1.4 is "standard" the 1.6 is a "stroked" 1.4, the 1.8 is a "stroked" and "bored" 1.4, or a "bored" 1.6
you cold essentially put the 1.8 in the aveo just as a long block if everything match up like i suspect. And then plug in the computer. I have yet to find the specs on on the american built 1.8, but the 1.8 korean/holden/opel/vauxhall is that way.