1. Prepare a grill for 2-zone cooking. On a charcoal grill, place a chimney full of preheated charcoal briquets on one side of the grill’s charcoal grate in order to create direct and indirect cooking zones. Adjust the grill vents to bring the temperature to about 325°F. Add 2 to 3 chunks of your favorite smoking wood to the charcoal for flavor. On a gas grill, adjust the temperature knobs so that one half of the grill is off and the other half is heated enough to maintain a temperature of approximately 325°F on the indirect side.
2. As the grill comes to temperature, pat the pork sirloin dry with paper towels. Using a sharp paring knife, make a ¾-inch deep incision in the sirloin for each garlic clove. Use your fingers to insert the cloves as deeply as possible in the incisions.
3. Once the grill is ready, place the pork sirloin on the cooler side of the grill as far away from the heat source as possible. Set the lid on the grill with the fully opened top vent positioned directly above the pork sirloin in order to force the smoke over and around the meat. Allow the roast to smoke for approximately 1 hour until it reaches an internal temperature of 145°F.
Clint Cantwell, Grillocracy