From a "Cooks Illustrated" email. Haven't tried it.
If only "enhanced" pork is available (it will be stated on the label), do not brine the roast. Instead, simply add 2 tablespoons kosher salt to the black pepper seasoning. With minor adjustments, a roast larger than the one called for can be cooked using the same method. For each additional pound of meat over 3 pounds (do not use a roast larger than 6 pounds), increase the salt in the brine by 1/4 cup and the water by 1 quart; also increase the oil and pepper by 1 teaspoon each (if using a spice rub, increase the recipe by one-third). Because the cooking time depends more on the diameter of the loin than its length, the cooking time for a larger roast will not increase significantly. After rotating the roast in step 5, begin checking the internal temperature after 30 minutes of cooking.
Serves 4 to 6
3/4 cup table salt
1 boneless pork loin roast (blade-end), 2 1/2 to 3 pounds, tied with kitchen twine at 1 1/2-inch intervals (see illustration below)
2 tablespoons olive oil
1 tablespoon coarsely ground black pepper , or 1 recipe spice rub (see associated recipes)
1. Dissolve salt in 3 quarts water in large container; submerge roast, cover with plastic wrap, and refrigerate until fully seasoned, 3 to 4 hours. Rinse roast under cold water and dry thoroughly with paper towels.
2. Rub roast with oil; sprinkle with pepper or spice rub and press into meat. Let roast stand at room temperature 1 hour.
3. Meanwhile, soak two 3-inch wood chunks in water to cover for 1 hour; drain. About 25 minutes before grilling, open bottom grill vents. Using large chimney starter, ignite about 5 quarts charcoal, or about 90 individual briquettes, and burn until fully ignited, about 15 minutes. Empty coals into grill; build modified two-level fire by arranging coals to cover one-half of grill, piling them about 3 briquettes high. Place soaked wood chunks on coals. Position grill grate over coals, cover grill, and heat until hot, about 5 minutes; scrape grill grate clean with grill brush.
4. Grill pork directly over fire until browned, about 2 minutes; using tongs, rotate one-quarter turn and repeat until all sides are well browned, about 8 minutes total. Move loin to cool side of grill, positioning roast parallel with and as close as possible to fire. Open grill lid vents halfway; cover grill so vents are opposite fire and draw smoke through grill. (Internal grill temperature should be about 425 degrees.) Cook 20 minutes.
5. Remove cover; using tongs, rotate roast 180 degrees so side facing fire now faces away. Replace cover and continue cooking until instant-read thermometer inserted into thickest part of roast registers 140 degrees, 10 to 30 minutes longer, depending on thickness.
6. Transfer roast to cutting board; tent loosely with foil and let rest 15 minutes. Internal temperature should rise to 150 degrees. Remove twine; cut roast into 1/2-inch-thick slices and serve.
Tying Pork Loin
No fancy knots needed -- just use double knots to secure pieces of kitchen twine
at 1 1/2-inch intervals.