That intrigues me that all things being the same the 383 only produced 20 more hp. There was a guy here in town with a Monte SS that had a 383 in it. I don't know about his top end but his car was wickedly fast. I think he said it dynoed aroud 700 hp. maybe he was lying maybe he wasn't. Couldn't drive across town without him wanting to race. I heard he ended up blowing it up, but one thing for sure it was fast