Originally Posted by Rick
Good work so far
Just had a look at those figures from CNC heads. According to them, a Zetec head flows more than a YB in std form - which as you will know - is total garbage.....
Rick.
The peak lift flow from a YBT head is very similar to that of a Silver-top zetec - I've tested them on my bench. In the lower lift areas the YBT out performs a Zetec due to it's better port shape and larger valves.
Also, when we produce a 500+ Zetec we only work the last inch of the port and fit slightly oversize valves. With a YBT you need to enlarge the throat to 25mm per port to get similar HP figures.
With regard to maximum achievable flow through the heads, whether Zetec silver top, YBT or St170, the figures will be something like this at 10" H2O.
Zetec silvertop 145CFM
YBT 195CFM
ST170 182CFM.
Yes, the YBT will achieve a huge flow figure, but in order to do this you need 29mm runners, and this causes low velocity and a very soggy feel (compared to Std). The ST doesn't need a huge port, and as such the velocities are still good and the engine will feel sharper.
Hope this helps provide an alternative perspective on potential.