Pump gas compression ratio..............
 to the Forums.
Widely discussed subject in the Steet Topic; search, and you will find a lot to read on the subject.
If you wish to reuse the 670 heads, dished pistons will be necessary to lower the compression for pump gas. Other larger chamber Pontiac heads can be obtained from Forums members or Ebay to lower compression as well. Since you don't list your location or what octane you have available in your area, it's diffucult to determine your maximum compression limit.
Les
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Les Iden
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'65 Buick Sport Wagon Custom, 340, T350, 3:23
'66 GTO Post/468, 700R4, 3.31 (Mike's as of 9-16)
'68 Grand Prix/455, dual AFBs, T400, 2:93 posi (sold)
'72 TA tribute/461, T400, 3.08, (Russ's as of 9-16)
'97 Mitsubishi Eclipse Spyder Turbo, Konis, 5 speed
'09 Torrent GXP, nav, Sun & Sound pkg., Bilsteins
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