what causes engine smoke to come out defroster vents?

[R72K5]

got HEI swapped on to the 250 engine in the ventura and after i warme dit up and revved it up a bunch to clear it out and stuff it started poutting engine smoke out the windshield defroster vents and fogging up the windshield just above the vents,

what causes that ?

engine is old original to the car and tired but runs billions of times stronger now though, before with the old points setup it could barely run at all was so weak



thanks

 

[Z3PR]

Are you sure it's exhaust ??? Only thing I'm thinking it could be is a bad heater core. Sure it's not coolent mist instead of exhaust smoke ???

 

[bablazer73]

I was say the same thing about heater core. But, if the engine was smoking externally, like an oil leak. It could have gotton picked up by the heater through the cowl panel and sucked into the heater.