Its been a while since doing any head work as I have been really busy building a Fisher Fury and working on my Ginetta G15 - the G27 V8 really has taken a back seat and absolutely no engine work.
However the recent posts and digging out the bench to test a head has encouraged me to complete what I started.
Shrouding.
Pictures below show the level of shrouding when the valve is at .4" lift which is the 0.25 dia figure - the white stick is on the edge of the valve at right angles and is 8mm long providing the 0.2 dia figure
The 0.25 D curtain and the 0.2 D annular being the figures that indicate full valve flow area.
This is a 3.5 deep chamber head - the shallower 4.6 heads have a different chamber shape not only due to the depth of the chamber but it also has less "shape" The shallow chamber reduces the chamber shrouding and gives an increase in available flow.
As can be seen above over 90 degree of the valve area is compromised by the chamber and the bore wall and there are good improvements to be made with careful reshaping of the chamber.
The bigger valves the restriction to the curtain area is enlarged and further work is required in the chamber to reduce the shrouding.
If you carry out the work to remove and shape the chamber to reduce the shrouding as much as possible on the higher lifts you also make greater gains at the intermediate lifts.
