Is it a big deal if the vtec smokes?

My buddie has a 97 Honda Prelude with a vtec engine swap. He told me the old engine (which was also vtec) was fine but there was something wrong with the compression. So he sent off the old one, had it fixed, and meanwhile put in a new vtec engine. But now with this engine, he says when the vtec kicks in the vtec smokes. When it idols the car is fine. The car could set there til the battery died idoling and it wouldn't smoke but when you rev the car up and the vtec hits that when it smokes. I'm not sure what that means but he wants to sell me the car and he says I get both engines. So my question is is it a big deal if the vtec smokes. Is it an easy fix. I'm thinking it could be the gasket. Maybe it needs a new head. I'm not sure. Ideas on how to fix it, or is it worth the buy.