It's not just the internet. I first ran into that myth too back when I was 17. Yeh, couple million years ago. LOL. What got me further advanced was to try next bigger cam after I did what everyone said to do - including engine builders, speed shops (see I told you long time ago) and regional gurus. Bigger cam worked well, tried bigger, that worked well, and so on and so forth. I ran 89 on the street and 92-94 (I miss Sunoco !) on the water, both with relatively low compression and pretty large cams. 9:1 to 9.5:1 was my target, some snuck in at 8.8 or so...lol.

Main thing is just like your original posts asks, get your quench good, aand get your compression good,,,,however, 87 octane may hinder these things performance wise.

I hate to agree, but I have to. So you don't feel bad, On the other side of the mtn of me and Matt, borders ME.

It's an area in NH (there are others of course)where Men are Men, and so aren't the women. Hah !

Ummmm, there's a dock that supports you ? Shipyard access maybe ?

OK so I get quench in line, then set compression. I'd like to run 87 but can go to 89, no moreal unfortunately because that's what's available. Once I nail the cam down I can figure it out, but does low 9s seem within reason? It will be measured not guessed.

imo,a 9 to1 n/a engine can run on 89 oct till the cows come home with the proper tuneup,87 could also work but timing&fuel curve will be real important.also,forget about extended tip plugs.i would also try to run a cooler water temp.

Mike, my plan is to weld a bung in the riser of the Gil exhaust to run an afr gauge so tune can be set as needed. In Maine water/air is relatively cool.
Depending on the cam specs, especially intake closing event is going to determine the compression. I don't want to overthink it but want to be at max safe. Id like to be 9.5 but that seems to be pushing it.

I wish you had said this sooner. now I have to spend the day grinding out epoxy!

If you really want to wring it out, have you given any thought to putting closed cooling on them and going to aluminum heads?

There is alot of factors that play a part of combustion, and what you can get away with. It goes much deeper than a static compression number. Piston style, chamber style and finish, quench area, coolant temperature, air temperature, camshaft, cylinder head material, spark plug design, ignition timing, and so on. .

A poorly designed setup can knock , even with stupid low compression, and a well designed setup, can go trouble free, with a higher than normal static compression.

I had dozens of guys tell me 9:1 compression, .060 quench, 155psi cranking compression, a roots supercharger without an intercooler, simply wont work. But, to the contrary, it has ran for the past 4 years with 6lbs of boost, and have ran as low as 91 octane in them. Being cubic inch limited, building a traditional 8:1 roots setup, would have gave me, well, tradtional power. Most typical supercharged marine 454s are between 600-700hp around here. Because they have been told its a small engine, so use a small blower, small carb, small cam, small heads, etc, and therefore, following that recipe, is a sure way to small power output as well.

I dont think your engine being a little wider than textbook optimal quench the SAE has determined, is going to net you a detonating time bomb. Stock merc engines ran that setup in many bbc marine engines, with poorly designed 1960s GM iron open chamber heads. I think the dart 308 is an excellent cylinder head, and will work nicely on your build. Focus on the assembly itself, valvetrain setup, and proper tune. Being off .010-020 from textbook ideal quench, imo, is nothing compared to being off on the tune, IE, running lean, incorrect timing, incorrect plug heat range, incorrect plug style, too high of coolant temps, poor fuel distribution, and so on.

Is the 308 the ideal head for what youre doing , eh, no. Would you do better witha smaller oval like the dart 275 , afr 265, trick flow 270, etc, im sure. How much, idk.

I do know, the average 489/496 stroker marine build, 89 octane setup, with a decent set of aftermarket heads, roller cam, usually do 575-600hp.