Clintonville, Wis.-based Performance Conversions has received an STC for installing 751-shp Czech-built Walter M601E-11 turboprop engines and five-blade Avia propellers on the King Air C90-1, C90A, C90B, C90SE and E90. The conversion, approved last April on the basic C90, also decreases cabin noise, takeoff distance, routine maintenance costs and downtime for engine maintenance, according to the company. Cost of the conversion is $530,000, a figure that customers can reduce by selling the removed Pratt & Whitney Canada PT6s and propellers themselves. Downtime is about eight weeks. At press time the company was nearing completion of its second and third conversions. A converted airplane will be on display at the NBAA Convention later this month, and Performance Conversions will be exhibiting at Booth No. 6653.