Take the roast out of the refrigerator and let it come to room temperature about 45 minutes before roasting. Heat oven to 325° F. Place the roast on a metal rack in a roasting pan, fat-side up, and rub with the chili and salt. Toss the sweet potatoes with the olive oil and place around the roast. Cook until an instant-read thermometer inserted in the center registers at least 120° F (for rare), about 1 hour and 15 minutes (15 to 20 minutes per pound). The potatoes should be fork-tender. Remove from oven. Loosely cover the roast with foil and let stand 10 to 15 minutes. (The temperature will rise to 125° F.) Slice half the roast. Serve with the sweet potatoes. Wrap and refrigerate the remaining meat for another meal.