Hi Richard,
I fear you may be thinking in the wrong direction!!
Firstly, unless there is a compression leak, in simple terms, the cylinder head as such cannot significantly alter the compression of your engine of its own accord. Also, I do not understand your terminology of a “squished” head, as a squish-band profile as such is impossible to obtain by virtue of the design of the piston deflector profile.
I also think that you are measuring the combustion volume of the head incorrectly – i.e. the combustion space with the head removed, as a volume of 74cc would provide only a compression ratio of 5.0:1 and 86cc only 4.4:1. whereas the standard compression ratio (allowing for slight variations) of a DPY engine is 7.2:1.
As the resolution of your problem may be more complex than can be encapsulated by postings on this forum, If you care to let me have a contact number, I’ll gladly discuss further if that would be of assistance.
Alternatively, I suggest you make contact with someone who really knows cylinder heads – for whom I refer to Alan Noakes, as he resolved my cylinder head problem by machining and fitting new combustion chamber “skulls” with a ten day turn-round and at very modest cost.
