My 68 390 is still using oil. A qt. every 100-120 mi. Bad re-build from the start. 1. Stretched head bolts-replaced. 2. Valve job complete- stopped the smoking. Everything is new. No smoke, no oil underneath or on the floor. Still uses oil. NOW WHAT?

 

If it is using that much oil you are just missing it somewhere. If it is not marking it's territory then it almost has to be burning it. I guess it could be going into the water but I would think that easy to find. It may not be burning enough at idle to see. Have somebody follow you while driving & just drive normal at first then a time or 2 nail it like you are going to pass someone. Whoever is following will let you know. What does your tailgate look like? Little oil spots?

 

is it using much less oil?
is it possible it still "running in?"

 

Torque-to-yield headbolts? That's a new one on me for this era of engines.

Blip the throttle. Got smoke?
2x with above... sooty exhaust with small flecks?
Is there a light haze behind ya while on the road?
PCV in working order? Is the splash shield under valve cover intact?

 

1qt every 120miles is a lot , it's going somewhere . pull plugs how do they look ? I am guessing wet .

 

I will mention those things. Thinking now that the rings haven't seated. Maybe?

 

Thinking now that the rings have not seated. Maybe? Less than 3,000 mi. on this motor.

 

Rings should have seated by now , something is not right !

 

Out of curiousity, did your engine builder bore it out and then match pistons and rings to that spec? Not trying to insult anyone I just think outside the box.

 

jefffafa ,, that would do it

 

have you done a compression check ? if so what was the numbers?