[66Submarine]

But to gain 6MPG from 12MPG would mean the engine was running really, really poorly before. Since the PCV valve obviously doesn't effect power from timing or anything else like that, the only way I can see you burning more fuel is to just somehow dump it in there in the form of a super-rich mixture, which should also be pretty obvious, IMO.

You keep saying that it doesn't work because your engine isn't absolutely factory spec for a lame truck 283, but how radical is it? GM made stuff like the 283HP 283, DZ 302, 350HP 327, etc. and put those into cars with no issue, and there are thousands of user-made hot rod SBC's being driven every day without issue with the factory PCV setup. I just don't understand why a mild hot rod 283 should have any issue.

That's not to say the magick PCV isn't a better PCV valve, but there's a difference between a PCV valve not being optimal and the truck burning 50% more fuel...