Originally Posted by zetaboostboy522bhp

hi mate the silvertop head needs cnc port matching (mild porting) by cnc heads which are the best in the business , 1mm oversized valves uprated guides etc , standard exhaust cam , custom inlet cam . if you use standard cam followers you are very limited in which cams you can use in terms of how aggresive the profile is if i remember right as it was a few years ago now lol. you would need to speak to ian howell or a cam company to make you one but i know ian used piper cams to make his custom cams and they would not remake them for anyone else. kent cams and cat cams said they couldnt make it if i remember right for my engine which is why ian got cnc heads to machine the followers to a larger hole so he could fit larger hydraulic followers from the ecotec engine which then opened up the choice of cams profiles to use , this cost around another £400 on top of the £1300 cnc big valve head. i chose not to have this done and stuck with the standard size followers and it still make great power 522bhp @30 psi. my head did not reach choke point either it was still making 38 bhp per 1 psi of boost but we decided to stop at 30 psi because of the headgasket etc.
the st170 head is by far the best head in terms of flow to use and already comes with 1mm oversized valves as standard or the silver and blacktop heads so you could gave 2mm oversized in a modded head. but you would need to mod the cam belt system if your on a silver top block which again causes headaches then theres the warping issues that surround the st170 head so the choice is yours really. also the focus rs is a blacktop head so again you would need to mod the cam belt system.

iam also finding it hard to believe that a zvh has made 480 bhp knowing how hard it was to get the power from the zetec engine. as i am also very good mates with ian howell (the man who invented the zvh engine ) he has a customer called sid who chucks money at his car like its going out of fashion , that has the best of everything and that has only ever seen around 380bhp at a sensible boost say around 26psi and that is always breaking , rockers smashed , pulling studs from the rockers etc and i know it one of those projects ian wants to get over 400 bhp from and he even has trouble. it been on the engine dyno about 5 times lol
i know the karl morris red s2 ran 400 bhp on a 1.6 cvh but i also heard that it was running 40 psi which is why it always broke.

hope this helps

cheers paul