Power Engineering made these in fairly large batches around 1990. The aluminium does a slightly better job of damping the valve train noise than the thin steel of the standard cover. Unfortunately for PE jsut as they started selling them Ford sold off all their RS 16i covers at half the price PE were asking for their's so not may were sold which led PE to put them on offer to Performance Ford readers - if anyone can remember that far back. The old school PE lot like Mervyn had to spend hours machining the fins flat on those things.