Okay I'll start
11 or 12 to 1 according to Motor Trend
The head design and material are a factor
Piston shape and camshaft profile are factors
For instance I can get away with 87 on my 69 Boss 302 at 5000 feet elevation
The pent roof closed chamber heads ping less than several other designs
Aluminum is also better (better heat dissipation)
I run some Sunoco 110 in it just for the smell (I add a gallon or two, when I want the smell)
Few years later they came out with 205 turbo heads they called them with angled spark plugs
The angled spark plugs helped smooth out flame propagation and lessened the detonation
Generally speaking under 11:1 is going to be something good to shoot for. Good cylinder head, moderate camshaft, and well tuned you should be fine. Just check the plugs when running it initially to get timing right.
Also, an engine that runs at 160* will have a little more detonation resistance as one that runs at 220* so lower coolant temperatures are your friend. As well as having an ACTUAL cold air intake, not one that sucks from right behind the radiator.
If you have a builder, you should get his/her advice. As others have mentioned, CAM selection and many other aspects of hte build can have a say in what gas should be used.
I built my 408w stroker with 10.5:1 because of the way they change the ethanol blends between winter and summer..
Im also running a camshaft that delivers max torque and engines built like mine are pretty prone to popping an upper ringland when powering the engine up from down low and cylinder pressure goes through the roof....If I ran 11:1 Id have to run atleast 97 octane...
The reason why I built it that way is because its pretty fun when you dont rev any higher than 5500 yet your up over 100mph running next to a guy whos screaming 6500-7000 rpm's and it doesnt sound like I'm racing down the highway....
Ive been cited for reckless driving in my 69 Olds442 w/441cuin SBC w/a 350turbo transmission w a 4000 stall converter ,purple hornies attached to longtube headders and a 411 rear quite a few times and paid hefty fines.. When I hit the gas to get the car moving when the light turned green it sounded like I punched the gas off the line...I tried explaining to the cop about the camshaft n converter plus gearing and he said tell it to the judge....LOL
Now I build my performance engines for the street with such brutal lowend torque they get up to speed really quick n effortlessly through the Magnaflow cats n the mufflers and it doesnt even raise an eyebrow of the local fuzz yet Im still having fun plus also saving my valvetrain from heavy high rpm abuse and always having that feeling like its futile to defy gravity by being sunken into the seat with some nice force is a pretty awesome feeling without the diesel smell or the black soot..........LOL
From 3100 - 4400 rpm's my 408w on a carb on the dyno was belting out from 568 down to 535ftlbs of torque yet only putting out somewhere between 327 -350hp...At 5500 the engine is pumping out 509ftlbs torque and 464hp. Not one time does the torque and hp crossover on the graph either.....LOL
Im running it with a QH and EFI also a TKO600 w/.64 overdrive and a 3.55 gearing too....
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We've talked in the past about the relationship between horsepower and torque. They work together, and horsepower needs torque to make you and your car happy. There's one magic number though that doesn't get much ink spilled its way, virtual or otherwise. The number is 5,252, and it's the point...