Hi Rodrigo, nice bit of machining, but....
I don't know you background, skills , experience, tooling, etc. So I stand to be corrected by experts, and will learn on the way.
I am an engineer, not a fully trained machinist so may have a different perspective from machinists, but not necessarily wrong.
My ideas, based on a teenage apprenticeship in a machine shop, 43 years as an engineer in industry, including some in engine manufacture.
All machines have some mis-alignment, no matter how small, and we aim to overcome this with the "correct" set-up , wherever possible. I see you have the workpiece in the chuck, boring from the main slide. Any mis-alignment between the slide and headstock will cause a tapered bore when set-up this way. With a very accurate lathe this should not be a problem, as the taper over a short length of bore should be well within tolerance limits for the part.
But the theoretical best set-up is to describe a circle with the tool, and progress this circle through the bore. This gives better parallelism of the bore. So when proceeding to your next engine, make a cylinder mount to clamp the cylinder to a datum face, clock this from the chuck to ensure the datum face is truly perpendicular to the axis of the chuck, affix the pre-machined cylinder - which should have allowance for finish boring. Then use a boring tool (mounted in the Mainshaft taper) and progress the tool through the cylinder. This then replicates industrial Boring machines, to give a true circular bore that is parallel and only needs honing to finish.
If anyone wants to teach me the errors of my ways, I'm ready to learn some more!