Porting the
Zetec is a straightforward operation, on the inlet side there is a lot to do
around the valve throat areas where there are many ridges at intersections
between the casting and the machining on the valve throats, the throat sizes
also need enlarging by 1-2mm o 16516k1024q r so, the inlet ports require enlarging by about
2mm (to 26mm on 1.8/2litre heads, to 24mm in 1.6 litre) all the way through to
the valve throat with a little taken away from the valve guide, the short turn
(bottom turn of the port) requires a lot of work to give a smooth radius into
the valve seat area. A 60 degree cut before the valve seat is useful, although
I generally blend this to a radius. The valve seat should be around 1.5mm wide.
The exhaust ports require some enlargement (2mm or so) but more importantly
they require a lot of straightening out immediately after the valve seat. There
is a large lump in the port in the bifurcation between the valves, this needs
reshaping to remove as much as possible of the turn whicxh effectively
straightens the port. To achieve this the bifurcation requires some
considerable thinning down at this point, be careful here since there is a
waterway within the bifurcation, the throats of the exhaust also require much
work just like the inlets in removing steps and ridges, the short turns require
radiusing and blending in. The throats should be enlarged by 2mm or so and a 60
degree cut/radius applied with the valve seat width left at around 1.5mm. The
throat shape should approach the shape of the inside of an egg-cup.
The chambers require very little work other than removal of sharp edges or
protrusions of the valve seat inserts. The backs of the valves require a 30
degree cut blending into the valve seat which should be about 1.5mm wide on
both inlet and exhaust. The leading edge face of the exhaust valves should be
radiused. Make sure the valve seats in the head are cut wide enough, often they
are not cut correctly to fit the valve especially on the exhaust side and that
limits the ultimate size of the valve throat.
The cams used are the 775/622 profiles from Piper, these are in the Piper catalogues as BP285H cams, they work with the stock springs and followers, with the cam set to 120thou lift at TDC on the inlet and 100thou lift at TDC on the exhaust, a 2litre with head as modified in the above instructions (and as shown in the pictures) will, with appropriate induction (45 DCOEs or Throttle bodies) and a decent 4-2-1 manifold should make around 200BHP and 170ft/lb+ of torque.
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