We have to relearn what Detriot learned very expensively in about 1977 when Ford opted out of doing high compression stratified charge i4 and V8 engines. Today, when we fiddle with our 170, 200 and 250 cubic inch engines, we have to use the knowledge of Dynamic Compression Ratio. Back in the late 70's, the ditched development work Honda and Ford USA did on a variant that became the overhead valve High Swirl Combustion 2300 four cylinder engine was all about how much compression you could generate with an aggressive spark advance curve. A foundational part was that Dynamic Compression Ratio (DCR), using seat to seat specs for Intake timing specifications.
See
http://www.wallaceracing.com/dynamic-cr.php, and put in the stock 240 duration or 256 degree duration Ford Motor Company Inlet Valve Closes After Bottom Dead Center figures with the stock 22 thou thick gasket and stock combustion chamber volume. That is the
minimum amount of Dynamic compression you should have. As you go up in Inlet Valve Closes ABDC, the amount of Static compression goes up. There is a limit to how much compression increase you can tollerate, at that point, if you can't raise the Anti Knock Index of the fuel from 87 to 93 or 95 or 100, then you have to start special engine tune management techniques like knock sensors, strain gages, engine fuel verses ignition mapping "fuzzy logic" like Mitsubishi does on its 2005 3.8 V6 or mixture motion work like the 1980 onwards Raymnond Mays Jag HE, 1981 Porsche 944 TOP, 1984 Ford HSC, 1985 to 1991 3.3 or 4.1 Alloy Head Falcon, 1986 US Fox Mustang GT 5.0 EFI or 1996 on Chevy Generation 3 LS1 style engines. These engines ran very high compression ratios by inducing mixture motion into the cylinders, and then ran a special fuel and igntion management system to look after total ignition advance. Jaguar, Porsche, Ford and GM started down the line of high swirl to avoid going to higher octane fuel, its the same thing Mike W's Classic Inlines head used in its engineering. Extra paddle wheel mixture motion on the intake allows you to run higher compression. Honda and Ford worked on this when they looked at the Stratified Charge Four cylinder engine in 1976, but Ford opted out when it realise how tight the production tollerenaces were going to have to be to build the engines. Honda decided to go it alone with its CVCH 1602 cc Accord and 1335 cc Civic engines, and also did some extra work for the Australians in the late seventies to make the first X-flow alloy Falcon 3.3 and 4.1 cylinder head in 1980.
That dynamic compression figure above from the stock engine, is best based on a 256 degree cams valve closing event. It is the one to preserve. If your cam goes up in duration, the static compression ratio can go up a large amount to preserve the stock dynamic compression ratio. So a 300 degree cam with 40/80 timing can cope with a 10.5 to compression ratio, but still have no more dynamic compression than a stock 200 or 3.3 1981 engine with a 256 cam with 22/54 timing and 8.4:1 compression. That Dynamic compression ratio calculation figure given is very important.
You can do even more than just reading it, you can tune some aggresively timed engines and still run it on pump gas. Like this little 11.04 seconds at 134 mph, 487 hp, 29.3 mpg Civic with 11.2:1 compression, M62 supercharger. The company director who owned it back then was from Endyn, and it shows you what can be done if you raise cam timing only enough to preserve dynamic compression. Not only does it have that 11.2:1 static compression on pump gas...it is supercharged with boost variable from12 pounds to 27 depending on operating conditions.
See
http://www.hotrod.com/featuredvehicles/ ... _civic_si/
The key to working the tollerances on the Ford six is the same with as any engine. Fact is, dynamic compression figures and Knock sensor tuning are what Ford US and Australia have used knock sensors from 1981 and 1986 respectviely. That little 1989 Civic Si above uses a GM knock sensor to retard timing a massive 20 degrees total on what was there anytime it picks up piezo induced knock.
The tuner should know, he got busted for using a knock sensor in NASCAR...
http://www.hotrod.com/featuredvehicles/ ... to_13.html
excellent getting the ignition right will help you get all the power your engine is capable of.