You can perform a leakdown test by putting compressed air into the cylinders,using an air hose fitting in place of the spark plugs.You need to put the piston at TDC on the compession stroke(both valves closed)and you might have to keep the crank from moving when you apply the air pressure,put it in gear if its a manual tranny,and block the wheels-an automatic is a little more difficult,you can use a breaker bar on the harmonic balancer bolt,or wedge something in the fan belts.Once the air is applied,you can listen to hear where its escaping from--bad rings or pistons or scored cylinders will allow the air into the crankcase,that can be heard at the oil filler tube or valve covers.Bad valves will leak air out of the intake or carb(intake valve)or the exhaust pipe(exhaust valve).Bad valve guides can consume quite a bit of oil,when coasting down hill a lot of oil can be sucked into the combustion chamber and burned,sometimes without that much smoke.Usually a plug will foul if its drinking a lot of oil.
Some rings take a long time to wear in--some never do--might be wise to wait a little longer,see if it gets better.Make sure the PCV valve is working,and if you have any fancy valve covers,make sure they have a breather--many aftermarket ones dont,and that will make the PCV valve pull air from the crankcase,and pull oil past the rings.
All the big blocks I had only got about 500-800 miles to a quart of oil,they were high mileage motors though.Dont forget cheap oil can boil away without any smoke--use a good brand name oil--I've had old motors drink a quart every 150 miles,just by switching to Castrol 20w50 instead of "dime store"10w30,I was able to get 400+ miles out of a quart. /forums/images/graemlins/crazy.gif
