My EQ headed 408 Magnum came out at 10.3, runs fine on the pump 91 we get around here. I run a dual pattern Hughes 230/234, .52/.57" @.050" (as near as I can recall at the moment anyway). 750DP, air gap, 1 3/4 Super Comps, 2.5" exhaust, 904,2500 stall, 3.55 gears. I'm running 18 initial/36 total mech with a vac advance. Mech advance curve is slow (all in at 3200). I'm still fine tuning the whole package for bullet proof street driving. And I'm at 5K above sea level.
When I get to the track, I'll spike my fuel with race gas. My 9.0:1 Brand X equine with over head cam and aluminum heads will start to knock on your 2nd or third run down the 1/4 on pump 91, even pure gas 91 (or 93 at sea level for that matter). Not that I would do this, but were I to wring out the 408 in all three gears (on a closed course with a professional driver), I am quite confident, it would show no signs of detonation in any gear. Were I to repeat that exercise, I'm pretty sure it would be in my best interest to spike the fuel with race gas or octane boost like I would at the drag strip.
Normal street driving is a traction limited blast.
You can run a higher-than-you-think static compression ratio for a given fuel octane, provided your dynamic compression remains within acceptable limits. Your local density altitude and the altitude range you operate the vehicle in will have an impact on dynamic compression. Cam selection is critical.
http://www.enginebasics.com/Advanced%20Engine%20Tuning/Static%20vs%20Dynamic.htmlhttp://wallaceracing.com/dynamic-cr.phpWe'll see when I get to it, but I'll for sure I'll have to re-jet the carb and probably have to run octane boost or cut with race gas when I get this near sea level.
Now, how much power is that extra 0.8:1 compression getting me vs. if I had kept it around 9.5?? Not much with my setup currently. But I'm a head gasket away from an acceptable forced induction static CR (would still have to open up the rings), or real compression requiring real gas. Durability and flexibility were where I was going here.
