Static vs. dynamic CRs . . . my recent build-up
Calculated, static compression ratio does not take into account the closing point of the intake cam lobe or other variables that affect the compression that the motor "sees" when it is actually running. That is why Dave ("Nobody") has been able to utilise a CR of near 11:1 on pump gas by installing a suitable, long duration cam (As RallyBob so rightly said could be done!).
Have a look at www.kb-silvolite.com
and see their Tech articles on "Dynamic Effective Compression Ratio" and also the compression calculators that are on that site. All extremely interesting and puts a whole new light on CR's
Taking cam profile into consideration when estimating (calculating) dynamic CRs certainly helps explain why my 10.7 CR, domed piston, large valve, stroked engine runs on 87 RON without any pinging or resorting to retarded ignition.
'72 ported head with 45mm Opel intakes, 38mm Opel exhausts, 224°@.050"/.465"/110°LDA cam/solids, matched Opel single springs, 8 Opel intake retainers (lighter) and valve locks, rockers and lock-nuts from my 2.4.
'71 (stationary pump) block bored to 3.701", forged 94mm Venolia pistons with .100" domes, moly top rings, no-gap seconds, 3-piece oils, stock '71 forged rods bored for .912" Ford LW pins, .010"/.010" 2.2 crank, everything "zero balanced".
'73 timing cover with new timing chain and tensioners, OP relief spring tensioned 2mm additional.
'75 distributor with locked, mechanical only advance and Pertronix, advance weights resprung, set at 10° initial, 35° total all in at 3000RPM, 6500RPM rev-limiting Bosch rotor, MSD5 multispark, Bosch "red" coil, Bosch WR7BP plugs at .040" (1mm).
Steinmetz SSD welded and ported (48mm) intake, single DHLA48 carb with 15mm trumpets inside fabricated cold-air plenum, filtered by K&N 78mm filter.
Old style, 4 into 1, HT coated header into 2.25" exhaust, turbo muffler and gutted "stock", twin-pipe resonator.
Remote oil filter and T-stat controlled "Volvo turbo" oil cooler.
Result: Street sweeping TORQUE MONSTER!