Hello Florian,
This head will likely take VERY large valves. My guess is perhaps 32 and 29mm. As such, the amount of material between the two seats will be minimal. This is the only area that might be a risk.
Further, the designer has chosen to remove material from the "squish" area opposite the spark plug and put a large relief area around the forward side of the intake valve (similar to the smaller relief of the standard A112 head). All of this will do two things. 1) Lower the overall compression ratio 2) Reduce the effectiveness of the squish effect, thus hampering full combustion.
Squish effect relies on the two surfaces (head and piston) being in close proximity (1mm or less) when the piston is at TDC. This forces the charge towards the spark plug and promotes better combustion, allows less overall ignition advance (because less time is required to burn the intake charge at high RPM) and reduces the occurence of pre-ignition and detonation. I would think that all of these attributes are desirable in a competition motor, so I do not understand the reworking of the combustion chamber, UNLESS it was intended to be used with some special pistons where the dome of the piston closely matched the new combustion chamber shape.
Lastly, as these heads are made by welding up the original intake passage and then drilling new passages for the four intake ports, two things will have occurred. Water cooling flow around the intake valve will have been disrupted and changed to some extent. I am unsure as to whether this might have any detrimental effect. Likewise, the effect of welding (application of heat) will have had an annealing effect on the head material and the welded areas are going to be a different metallurgy. Only if the head was annealed and re-heat treated, after the welding process was completed, might the material hardness be restored to that of the original casting.
Good luck with it.
Regards,
Paul Vanderheyden
Scuderia Topolino
