Preheat the Smoker: Set your smoker to 225°F (107°C). Use wood chips like apple, cherry, or hickory for rich flavor.
Prepare the Pork: Pat the pork sirloin dry with paper towels. Rub all over with olive oil. In a bowl, mix the brown sugar, smoked paprika, garlic powder, onion powder, salt, pepper, and chili powder. Coat the pork evenly with the dry rub.
Smoke the Pork: Place the pork sirloin directly on the smoker grates. Close the lid and smoke until the internal temperature reaches 145–150°F (about 2.5 hours).
Optional Glaze: In the last 15 minutes, brush the outside with BBQ sauce if desired for a sweet and smoky glaze.
Rest: Remove pork from the smoker and tent loosely with foil. Let rest 10 minutes before slicing.
Serve: Slice thinly across the grain and serve with your favorite sides!