 It was powered by a 5.7-litre Callaway-tuned C4B engine, based on the Chevrolet LS1 V8.Until recently, it was the most powerful Australian made production car and a true collectors item.The GTS came with a Tremec T56 six-speed manual transmission only when it was released in 1999 and was one of the fastest sedans in the world, if not the outright fastest.