I've heard that a newly rebuilt engine will use more oil during break in than once it is well broken in.

What are your experiences with this? What level of consumption is considered normal and when should it improve?

Northern,

This is my opinion / experience on rebuilt motors. It all seems to depend on what rings you use and if it's rebuilt correctly. Assuming that it's rebuilt correctly, then it seems to depend on how hard you run it. Engines that are run real hard may use a little more than a engine that is babied, but not much more. (If the engine is not getting beat on real hard) chrome rings seem to use around a 1/2 quart in about the first 500 miles. Moly faced rings will use around a 1/8 quart or maybe a little more in around the first 500 miles. Chrome rings do seem to take a few miles to seat. Moly faced rings seem to seat within a 100 to 200 miles. Anyway, once you hit the seating point, oil comsumption will drop right off to the point where it's not a concern.
I never done a re-ring job, so I have no input on that type of rebuild.
Having said that, I should add that I have never built a race engine, only street / fast street engines.

Fred.

After a very short break in , with moly or cast rings you should not see any oil usage that you could measure ....... the key will be the quality of the hone job,and matching the hone crosshatch to the rings and the roundness of the cylinders ..... so the better the machine work the tighter the seal If we are talking a BB then ensure you guides are perfect cause that can be a source of oil consumption too

Mine didn't use any and I used Mobil 1 from the beginning. 10W30.