I have a rebuilt 283ci. in my 66 chevy pickup. it runs great and has plenty of power but about every 150 miles it uses close to a quart of oil. i would have to believe it is bad rings because there is no smoke coming from tailpipe and I don't have any leaks coming from the oil pan or valve covers. anybody that can help, please do.  

If there is no leaks and the radiator is clean. then it has to be going out the tail pipe. How many quarts are you puting in? run it a quart low and see if it still goes down.  

No, i have no problems with the radiator. I'm running 5 quarts and it does not matter how many quarts i have in it it still uses oil. My question is, if it is burning oil, it is coming by the rings,right?  

YEP EATHER THAT OR THE VALVE GUIDES. Did you give it a velve job on the rebuild?
Maybe go to a auto parts store that has a machine shop like MAPA and see what they have to say?  

Is it a fresh rebuild? Shop built, or reman?  could be the cylinder walls are too smooth, or not crosshatched properly, and the rings aren't seated.  

This is my deal. the guy i bought this truck from rebuilt this motor did so about 10 or 11 years ago. i've had it for 3 of those. as far as i know it was not driven very often with the previous owner. i put the new intake and carb on it because the old carb kept flooding. other than that i have no idea about the internals of this engine. how long would it actually take to seat the rings if it was driven often?  

They should seat in about 1,000 miles. One way to tell is if you can find a adaptor to put air in the cylinder through the spark plug hole. If the air is going out the breather tub,you can put a tusiue over the hole and see if it fluters. If it coming out the intake its the valves. You can also do a compresion check and see how bad it is.  

Well its fixin to turn over 3,000 miles since i've had it so i certainly will do this. thanks for your help. if you have any other suggestions please share.  

Were does the crankcase breath through? does it have the old style breather tub or a pcv valve in the valve cover? Check the valve make sure its not pluged $5.00 get a new one. The crankcase has to breath or it will push oil out. You said you changed intakes I thought you night have blocked of the breather?  

It had the old style breather but i just changed valve covers with the breather in the cover but it has the PCV valve in the back of the motor beside the distributor. I took the cannister out of the lifter valley so the intake would fit. i do have the PCV valve hooked to the front of the carburetor though. am i wrong with doing this?  

I did the test you described above and there is air coming out of the breather hole in the valve cover. I did this on cylinders 1 and 3 and both had the same results. Do I do this on all of the cylinders to check or will this do? Also is there any way other way to get the rings to seat properly before tearing the block down to replace them?  

The pcv valve should be hoked to the bottom of air cleaner just inside the filter so it don't clog the filter.

Find someone with a compression tester and do a compresion check on all cylinder. Or you can buy one about $30.00. MAPA can tell you what the reading are supose to be,or they can do the check for you. Sounds like you got a poor rebuild when you bought the truck. Do you know if it was using oil before you changed the carb  

Correct me if I'm wrong, but the pcv valve connects to a vacuum source(carb or intake).  The crankcase breather hose connects inboard of the air cleaner, unless it is a breather/filter.  

Yeah thats what it sounds like. Unfortunately no I don't know if was using oil before I changed the intake and carb because I was not able to drive it because the old carb kept flooding almost every time i wanted to. So is there anything I can do to help seat the rings, or no?  

I'm with Curtis on doing a compression test. Plus, it gives you a chance to look at the plugs, to see if oil usage is limited to one cylinder, or up to all 8.

If the old carb was overfueling, it might be washed out rings, instead of unseated rings.  If so, then you will not fix the problem without new ones.