I have a bit of a mystery to solve, and haven't been able to come up with the right solution. Here is what I know so far. I rebuilt a 400 small block with new vortec heads and an Edelbrock 2116 vortec manifold. The engine runs well, but uses an incredible amount of oil, to the tune of 1 qt in 50 - 80 miles of city driving. There is certainly some oil smoke, but not as much as you might think. I pulled the engine to inspect the piston assemblies, and found them to be excellent, rings were installed correctly and they seemed to be seating well all around. I have done a leakdown test, and all cylinders are within 3%-6%. Next, I measured the clearance of the valve retainer to the guide seal and found it to be very close at maximum valve lift. The cam is very mild comp cam 260, with .440 lift on both intake and exhaust. I removed the heads and cut down the guides to provide more clearance, installed new guide seals, but there was no improvement in oil consumption. As I was working on the heads, it was obvious where the oil was entering the combustion chamber. The intake valves were coated with a hard oil residue on the underside of the valve, and up the stem. I was sure that the seal interference (about .010") was the culprit and that the oil was being forced from the top of the heads through the seals and into the combustion chamber. No such luck. I cleaned it all up and re-assembled, but no improvement. Yesterday, I pulled the carburetor and swabbed a clean cloth through the intake manifold runners, and there was a lot of oil on the rag, even before getting to the head. The oil seems to be coming through the intake. The obvious thing is the PCV valve, but the valve covers are baffled at the PCV valve and the vacuum line is completely clean and dry. Also, the intake manifold is not leaking. There is no vacuum at all when I block the PCV valve and the air intake on the valve covers. I'm using the GM manifold gaskets and when I've disassembled it, it appeared to have sealed well. There are no external leaks at all on the engine. I'm really baffled, and although I'm getting better at pulling the
engine apart, I'd like to figure this one out. Any suggestions on where to look next?

Thanks, and sorry so long!