Compression...

My opinion..Static ratio is not what you really should go by. It's what most guys use, but it's misleading. Static doesnt take into account the rod legth or valve timing. Both of which directly effect the way the mixture is compressed in each compression stroke. To generalize, 9.5:1 static is the accepted safe limit for pump fuels and iron heads. Anything over that and you may have detonation/preignition issues on available pump fuels. For around me, I can get 93 or 94, but from november to February they add extra oxigenation, and all year we run 10% methanol. The end result is, the fuel burns hotter and faster than it ever has. That can become an issue in 40 year old engine designs. That being said, I have several street cars running closed iron chamber heads with mid sized hydraulic cams (cams that pull 7-8" of vaccum at idle in gear) that run 10.8:1 static ratio. They run on the 93 or 94 pump unleaded. Why? Well, because the cam's lobe timing is such that the cylinder pressure is not too high at low (under 1500-2000) rpms and because the heads' chambers and ports are designed to keep good atomization and get decent swirl into the cylinder and good tumble as the piston comes up. That all adds up to a mix that is very well suited to burn fast, and is stable in the compressing stage so it wont ignite early or burn uncontrolled. It also means you can run less igition lead. So total timing in those engines is from 28-32° as opposed to 32-38°. It also takes setting the curve so it doesnt come in too fast. The Pump gas dyno monsters you read about in the engine masters use all kinds of trcks, and they end up with static ratios in the 12.5 to 13.5:1 range and run "pump" 93. OK, they arent good for anything other than a few hundred dyno pulls, and that pump gas surely isnt what comes from the ground..but you get the idea. Very generally, you can run up to about 185psi on unleaded pump fuels with open chamber iron heads without running into detonation threshold. Add a closed chamber head and/or a small dish in the piston, and that threshold rises. Add aluminum heads, that rises. Polish the iron to eliminate carbon deposits and hot spots, that rises. Bring the flat of the piston to the flat of the head (quench) that rises. Run a cam that closes the intake valve later, that pressure number will fall, but the threshold of detonation rises...Coat the piston tops, valve heads and chambers, that threshold rises. How much more you can run depends on how well it's all executed. I've done 10.8:1 big blocks with iorn closed chamber heads and flat tops, and 11.2:1 small blocks with dishes and modern aluminum heads that run well on pump fuel. I've also had 9:1 big blocks with large open chambers and no mechanical issues that I couldnt get to stop pinging no matter what the tune up was..lol. The best I've had for open chambers was a true 10.4:1 383 with milled 906s that pumps 185psi and runs like a top on pump fuel. A larger bore 440 or 400 may not run that well on pump gas. The KB-Silvolite.com site has a good dynamic calculator as part of a static calculator. Just make sure you have your cam card handy, and that all your info is inputted the way the thing says to. If you play around with cam timing, rod length, and chamber size, you can see how they relate to the cranking psi/dynamic compression ratio.

PS..never ask opinion...I'm too long winded :)