Compression ratio cannot be increased without installing new pistons, crank, or shaving heads. He increases the timing, which puts more pressure on the fuel mixture before ignition so it can get more power out of it.
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'13 Mustang 3.7V6 - MT82
'00 GP SE (L67 Swap, XP, Headers, 3.25")
'98 GTP, '01 Bonne