Start Your Engines

• WWizards of the Coast2016-09-20
  Official Ruling
  The set of Vehicles and creatures affected by Start Your Engines is determined as the spell resolves. Creatures you begin to control later in the turn won't get +2/+0, and Vehicles you begin to control later in the turn won't automatically become creatures and won't get +2/+0.
• WWizards of the Coast2016-09-20
  Official Ruling
  Vehicles you control become artifact creatures and then also get +2/+0.

Rulings via Scryfall