Search:

There are engineering "rules of thumb" for efficiency loss percentages for turns, transitions, length, diameter, etc... No need to guess.

For the first question: probably not.

For the second question, you are correct. The reason for the 1 larger size is bends...slow the air down for turns.

Before the turbo you want as little restriction as possible while maintaining smooth flow. Larger pipe helps (to a point as has been mentioned). The smooth, cool flow will yield more power than...