My 11/1 360 runs at a tic under 180 psi, with full-timing, full-time, on 87E10 ......... with alloy heads. With a small cam, overdrive, and a modest hiway gear, I think it could make hiway fuel-economy deep into the high 20s and still go 12s. Oh wait, it already did.
The point is, if yur gonna do pistons anyway, you don't have to lower your expectations. I mean you can but, you may be leaving economy in the back-room.
But if you have to run iron heads, for whatever reason, I get it.
However, IMO
running a lower compression and running cheap gas is a kindof loosing battle.
Assuming a price difference of 5% between 87 and 89;
If your car drives just 5% further on hi-compression and 89 gas, than
with low-compression and 87 gas, that is a break-even. 5% is just 10 miles on a 200 mile tank. If i goes 6% further, just 12 miles on that 200 mile tank, it's actually costing you less per mile even tho, more at the pump..
Furthermore; you only need just enough octane to suppress detonation.
If yur going down the highway with an 8/1 engine throttled down to an effective Dynamic cr of 5/1, it will burn any old skunk pee. So 87 is already a luxury gas. So you may as well bump the Dynamic compression ratio up closer to 8/1, which is what 87 will support with iron heads.
You say mild engine. If that means 2bbl, then the engine may never get past 70% Volumetric efficiency anyway, and so you might be able to run the Dynamic cr all the way up to 8/1 or more! still on cheap gas.
Jus tossing it out there
