I retired my Rover's original 10.5:1 engine in 2007 with 203,000 miles (327,000km) covered. Primary reason was the cost of rebuilding the original verses a cross bolted, top hat lined 4.6 litre Range Rover engine, running a custom ground camshaft. The choice wasn't difficult to make I can tell you. The big engine returned over 30mpg on more than one occasion, with the original engine delivering a best of 27mpg. One of my best decisions involving my Rover!