Means are provided for adjusting the relative timing of the two pistons so as to vary {HEAD ~ the compression ratio} of {TAIL ~ the engine} 
of
Means are provided for adjusting the relative timing of the two pistons so as to vary { HEAD ~ the compression ratio } of { TAIL ~ the engine }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL