What Quick says! 
Thought you wanted to tune the standard engine. Ofcourse when looking at most bhp another engine is always better. But where does that end.. I mean, get a 1.3 or 1.4.. or why not take a 1.6 or a 2 liter!
And every mod that you are gonna do have some positive and negative things to it.
When you go for lets say a CG13 it needs some electrics as well and perhaps some fiddling with fuel pumps etc and the allmighty driveshafts. Although driveshafts should not be a problem if you make those at a place specialized in driveshafts. Only expensive
It's not like you can just weld them together, they have to be balanced etc.
It's just the question what you want to accomplish. And fuel consumption? Did I hear you say something about fuel consumption?! :laugh:
