Karl

I have seen lots of cracked zetec heads! They suffer with cracks around the exhaust valve seats, that can spread through to the water jacket. (and spark plug hole, machined for flat washer plugs or not) If I can be bothered (or remember) I'll take a few pics of one to show you what happens. I've even sectioned one where they crack so you can see the crack running through to the water jacket! It only seems to effect turbocharged zetecs.

Flow bench figures are meaningless but I am not going to argue about it on the internet. They show nothing that correlates to what actually happens in an engine. I have, many years ago, spent a lot of time on flowbenches and created heads that on paper should create more power, but in practice do not deliver. The reason is because the flow test conditions do not replicate what is dynamically happening in an engine at all! The only way to design the best head is to port, test, port, test and keep on going until you have the best head. I've been doing this for 20 years with the CVH and probably ported at least a couple hundred in that time! I know what works and what doesnt!

My ultimate CVH head is nothing like a head you'd get from CNC heads! It has totally different ports (the head is extensively welded to achieve this) they have huge valve seat inserts fitted, and 40mm exhaust valves! The exhaust port at its narrowest is 36mm just inside the valve seat opening out to 42mm! Turbo engines are completly differnet to N/A's in terms of extracting power. The exhaust ports are the single most critical item! The zetec has absolutley terrible exhaust ports that with the best porting can just match an average cosworth head. Yes, the CVH may only have a single exhaust valve, but in my top spec heads, the exhaust port area is FAR bigger than the zetec and thats why we can make 500bhp CVH heads!

P.S. Let's not turn this into an argument, I'm trying to give a little insight into the strength and weaknesses of both engine types. The honest truth is both heads are terrible in terms of design. Both have advantages and disadvantages, the CVH requires SERIOUS work to make flow, whilst the zetec is more reliable for high revs but suffers from poor exhaust flow, but neither are a patch on the mighty YB!