You can use this chart as a general guideline for engine operation.

This one will give you specific range information based on weight, altitude, and power settings.
NOTE: This chart is for weights between 60,000 - 55,000 pounds, out side that range there are other charts.

Here's a link to a larger version of the above chart that's more readable.
http://332nd.org/dogs/baumer/Stuff/B-17G2.jpg 
Baumer