out, called it the best 1/18 model ever, then came the GT40, OMG! But to your question, the Grand Sports were fitted with a variety of engines during their short production run, only five were built before GM shut the program down. The most powerful and well known engine was the 377 CID aluminum small block with four weber side draft carburetors with a cross over intake manifold rated at around 550hp. Zora Arkus Duntov never produced a big block car but it seems a 427 was added to a roadster version, pure independent from GM.