The Lotus 31 was a purpose-built driver training car for the Jim Russell school. Russell wanted contemporary cars, but the Lotus 22 usually came with the lay-over Cosworth Mk11/MAE engine that had a rather expensive dry sump oiling system, Russell bought the chassis and with minor changes, had them fitted with upright Holbay 1000cc engines and Renault transmissions. The Lotus 31 eventually morphed into the Lotus 51 FF, which begat the Lotus 61, the usual chassis fitted with the "wedge" bodywork that Lotus was experimenting with during the mid '60s.