If using charcoal grill, place drip pan with ½ inch water directly under grilling area, and arrange coals around edge of firebox. Heat coals or gas grill for indirect heat.
In small bowl, mix all ingredients except turkey and butter. Loosen skin on turkey breast in 4 or 5 places. Cut butter into small slices; place randomly under skin of turkey. Rub chili powder mixture over entire outside of turkey.
Insert barbecue meat thermometer so tip is in thickest part of turkey and does not touch bone. Place turkey, skin side down, on grill over drip pan or over unheated side of gas grill.
Cover and grill over medium heat 30 minutes; turn turkey
Cover and grill 1 hour 30 minutes to 2 hours longer or until thermometer reads 170°F and juice of turkey is no longer pink when center is cut.
Remove turkey from grill; cover with foil.
Let stand 10 minutes before slicing.