Octane requirements
If you have an EFI engine with a knock sensor, then you can run whatever gas you want, the computer will dial back the timing to protect the engine. Yes, sometimes it runs like crap, until the computer learns the new gas, or the operator does.
But with a carb, you are the computer.
Octane requirement is highly Load-sensitive, or actually sensitive to combustion chamber heat, which increases with increased load.
An engine that might require hi-octane gas at WOT, pretty much doesn't care what it gets for steady-state cruising.
You may be able to design a timing curve to satisfy both. Or just do what I did; install a dash-mounted dial-back retard module, and adjust the timing on the fly, right from the driver's seat. Mine has a range of 15 degrees which is plenty.
IMO, 9/1 in a Magnum is just about right.......... for now, lol.
There are several tricks that you can do, to save an engine, that has a compression ratio that is considered to be too high for the gas you want to run. The major players are combustion heat, and cylinder pressure; which are often intimately related.. Therefore, the first place to start, is a compression test to see what the actual CCP(Cranking Cylinder Pressure) is. This will point you to a minimum WOT fuel requirement. Throttled, it will often run Part Throttle on something less than at WOT. Sometimes the low rpm timing has issues. There are tricks to get around that.
I didn't vote because the answer is, IMO, impossible to give, with the provided meager information.
>Cranking cylinder pressure is a more accurate indicator of the octane requirement than is SCR(Static Compression Ratio) especially in the lower rpms, say below 3200, or perhaps a lil higher.
>With iron open-chamber heads the empiracle evidence seems to point to the following;
91 supports 160psi
89 supports 155
87 supports 150
tight-squish chambers usually support about 5 psi more.
Some guys have learned to use a lil more pressure.
Some guys have lost engines on less.
>When you run on the edge, your tune has to be sharper, and the chamber temperature carefully controlled.
You can detonate engines even down under 140psi
>The goal of street-timing is NOT to force the engine to take as much timing as possible, rather, the goal is give it just enough to satisfy her. You will not, by seat of the pants testing, on the street, feel, 3degrees short of optimum.
>If the tires are spinning, the engine no longer cares about timing at that throttle/load setting, lol.
>Generally, it is more energy efficient to run the timing up, on better gas, then to retard the timing to suit a lower octane gas;
your cost per mile may be slightly higher, but your engine will be more fun and will probably last longer.
>There are two times that timing should be a concern;1) WOT; at 3500 and up, and at stall. 2)Part Throttle at Stall . Below stall, is basically a throw away, you do what you gotta do to achieve the stall to 3500, detonation-free.
>Without a computer, it is IMPOSSIBLE to give your engine the Idle timing it wants so; IMO, Idle timing is of LEAST concern, within the parameters of; 1) not being so high that it causes the transmission to jack-hammer the driveshaft and ring-gear when you put it into gear, and 2) not being so high that the Transfer slots dry up and this causes a tip-in sag, and 3) there is no such thing as running too retarded at idle. Idle-timing controls your idle-power. The more you give it, the more power she will have at idle. This is NOT necessarily a good thing, especially with a poor starter gear, of say under 8.60, but this is somewhat camshaft dependent.
AS for me, I would rather have to deal with a lil too much pressure, than a lot not enough.
IMO, 9/1 in a Magnum is just about right.......... for now, lol.