They do reduce the amount of air that travels around the engine in the summer and make it a little hotter. If nothing else,.. get them and give it a shot and find out. Some guys say that vented blocks to much and take them off in the summer. I leave mine on year round,.. and have used non vented and they stayed on year round.
Its one of those things that might work for you,.. might not... kinda like windshields.
For a wounded man shall say to his assailant,
'If I live, I will kill you. If I die, You are forgiven.'
Such is the rule of honor.