Originally Posted by Checkers
The EJ205 heads have a smaller bore than the EJ257/EJ255 shortblock. That means that the 'dome' of the combustion chamber doesn't fit perfectly on top of the piston. So rather than the combustion chamber being a smooth dome, there's a sharp edge that is a detonation hotspot and screws up the combustion.
$300 gets you machining to match the dome of the head with the larger bore of the shortblock, making the engine far less prone to detonation per Maxwell Power.
$3000 gets you lots of machining of the intake and exhaust ports (what people usually refer to as 'headwork'). That's not what Maxwell is talking about. He's referring to a much simpler, much cheaper procedure specific to the hybrid engine rather than generic expensive head work.
checkers is right.
Optimizing your combustion chamber is 350. Optimizing your ports is 1300.
the chamber is the most important for reliability and makes better power.
Ports are important for making even more power.