The original "Santa Maria Style" BBQ was top sirloin. The roast is cut into 3 or sometimes 4 chunks--cut in the same direction as if cutting top sirloin steaks. Slang for this cut of meat is "Top Block." The "Top Block" chunks are grilled over oak coals with Santa Maria style spices, then sliced thin and served. There is really no need to cook top sirloin "low and slow" as it is already tender. When tri-tip first came about it replaced "Top Block" as the main cut of meat for Santa Maria style dur to the cost of the meat. Tri-tip was very inexpensive when it first came out. Today tri-tip and top sirloin run neck and neck in price.