good mention about the springs, it gets where you are modding a 318 why not just start out with the good 340 360 heads with spring dampers etc. this is what gets me people say "there the same..." 318 and 340 arent the same.its in the details. The blcok isnt even the same there reinforcement near the drivers side motor mount ears...i get tired of the argument myself and hearing that they are the same...or "what difference does the bore make..." the bore doesnt make the 340 its a small part of it though. i beleive its more in the ability of the 340 to rev and the stout bottom end and the flow of the heads which allows for a bigger cam ...thats all the things the 318 doesnt have going for it. again this brings me back to my point why put a big cam in a 318 when the heads cant fully support it. OR I'd say do it but eventually youll add heads...porting a 318 head isnt going to make it a 340 360 flowing head.