I've searched all ove the internet for expected hp gain for this. I'm going to put a set of 4.3 vortec heads on a non vortec block with flat top pistons and carb. I currently am running the non vortec heads but know that the combustion chamber is a lot smaller on the vortec heads. Looking for some information of HP gain. I know this seems to be more of a v8 site but maybe someone here can give me some guidance. thanks