oil leak from exhaust???

just bought an 89 gmc vandura sl series with a 350. van runs great, has very good power for 170k on her. she has no leaks what so ever from anywhere. except the black residue/oil spilling from the exhaust when given alot of pedal. also, goes through about 2-4 quarts of oil a week depending how hard it's been driven. again, no oil leaks from engine. thanks in advance.......tim

Two to four quarts a week ?????!!!!!!!!!!!!!!!!!!!!!!!!
Thats not a real engine, its a very large oil pump !! Can you sell it back ? Because its smoked, the rings are gone big time, maybe replacing oil seals will slow it down, as will putting in thicker oil, but honestly I would dump it.Good luck.

wouldn't i lose comprssion if i had bad rings?

Have you done a compression test ? Its likely leaking past the oil control rings not the compression rings.
It could be sucking lots past the valve seals too.
The compression doesn't have to be way down there for it to pump oil.