I took my whole exhaust off today from the "header". I never got blue smoke at high rpms with my exhaust (cats included) in tact. As soon as I reved it up without the exhaust (at around 6k) a plume of blue smoke surrounded my car. When I put everything back together and reved it, the smoke disappeared. Any possible causes besides burning oil?

 

Ya..No Back pressure on the exhaust..so it is getting More Fuel.