is the focus rs head different to the st170 one in terms of ports and valve sizes?

 

I think st170 has bigger valves, not sure on porting. Does'nt st have variable cam timing?

Best head for the money imho for zetec is Ford Racing one from states.

 

Completely different heads. The only thing remotely similar is the size and shape of the exhaust ports.

 

St has variable cam timing,totally differnt units.
FRS has sodium filled valves though lol

 

so the st170 head is better flowing?or just has larger inlet ports

 

If that was true then you wouldn't be able to easily swap a ST170 head onto a 'blacktop' engine.

The detail of the valves, cams, etc. are different as it has high lift cams and, as mentioned, the VVT on the inlet cam. The inlet port is bigger and flows a lot better than the shape of the standard/RS head, but the valve sizes (but not stem lengths), angles, cam centre lines, etc, etc. are the same as the standard/RS blacktop.



Oh, and even the head chamber volume is the same......

Martin

 

Okay, to clarify my comment to fight off the pedants.. I was referring to the flow characteristics of the head as that is what is important in head related discussions.. I think you'll find the inlet valves are a different size too.. Try putting both heads side by side and doing a proper comparison

 

Which is exactly what I did over 3 years ago.....

Your forgetting that the valve sizes were increased from the Silver top in the Black top engine. I apologise, the ST170 inlet valve is 0.5mm bigger diameter.

As for being pedantic, not being remotely similar, I think is applicable to a comparison of CVH to Zetec head, not the subtle differences of the St170 one. Which as I said is a not too difficult swap. Many of the parts can also be used in a standard head. As an example, the solid top cam followers are a far cheaper way to go with high lift valves, than after market ones. Making it all work properly, as with anything, is another matter.

Martin

 

here's a little comparison for you . the first pic is a black top head with a deep reach 19mm socket in the inlet port and the second pic is a st170 head with the same 19mm socket in the inlet port . hope this helps clear things up a bit

 

Details, details. Its hardly "completely different".

The main reason you can do that is because the dividing wall between the valve throats is much shorter on the ST170, not the extra 5mm height of the port at the manifold face.

Martin