Originally Posted by Paul J
Pumaracing,
You say that 'A 2.1 ZVH will never rev very high because it doesn't have enough base flow for the big bottom end the head has been fitted to.'
As Matt asked how does the 8v CVH compare to the 16v Zetec head and what can be expected of both in BV versions?
Glad you've come on here and hope you stay.
As a rough guide, and std flow varies quite a bit from head to head (as of course does flow after modification depending on the skill of the modifier) they flow (or can be made to flow) as follows.
Std CVH - 140/145 cfm
Ported std valve CVH - 160/170 cfm
Std Zetec - 170/175 cfm
Ultimate Ported 45mm BV CVH - 180/190 cfm
Ported std valve Zetec - 190/200 cfm
Ported 33.5mm BV Zetec 210/220 cfm
By ported I mean by an expert with a flowbench who's put a lot of R&D time into it and not by someone with a flapwheel and more optimism than expertise.
As you can see a well ported CVH, especially BV CVH will match a std Zetec and get close to a fairly well ported std valve Zetec. However even a BV Zetec isn't going to turn a 2.1 bottom end into any sort of rev monster without using cams and turbos that are just not going to be very road driveable.
According to Ford my 2.0 Focus ESP produces peak power at only 5750 rpm and I have no reason to doubt that from how it drives. Increase the size of the bottom end a bit, drop the CR to 8:1, make the air go through an intercooler and several feet of plumbing before it even reaches the inlet manifold and that rpm would drop a lot further still. Adding the turbo won't alter any of this.
If high rpm for its own sake is a specific target for someone then tune a N/A engine with throttle bodies and cams or build a turbo one with a smaller bottom end. Personally I'm not sure what the big deal with high rpm is provided the car is geared correctly for its power output.
As for staying on here I'd never actually heard of this forum until yesterday when I was told that a thread apparently involved me in some way so I popped in to have a look. I doubt that time constraints will allow me to spend an awful lot of time in here but I'll have a look as and when I can.