I live in a pretty small town and all the gas stations that I have checked out only have 86 or 88 octane. If I can't find the Ford recommended 87 what should I use 86 or 88 for the best performance?

Right now I don't feel like getting my computer reflashed.

 

Use 88

 

I'd use the 86 first, if it pings I'd move up.

More power with the lower octane and stock tune.

 

I woudn't even take the chance, go for 88 only. The 86 is going to be lower qualiy anyway. 86 around here used to be "economy" gas. It probably still had some dino poo in it.

 

88 all the way. Why would you even think of going lower than the recommended octane?

 

Sigh. The recommended octane covers all bases right down to 110 degree days in California or Arizona where the engine/air/combustion chamber temperatures and pressures may be high enough to cause detonation.

Regular is 86 up here where I live. Everyone runs it, I run it with advanced timing in my '86. It's cooler up here and nobody has problems.

86 will give you the best performance.

 

 

You don't state what elevation you're at but . . . . as altitude increases the engines octane requirement decreases . . . just my .02

Here's some supporting documentation . . . .

"The effect of increasing altitude may be nonlinear, with one study reporting
a decrease of the octane requirement of 1.4 RON/300m from sea level to 1800m
and 2.5 RON/300m from 1800m to 3600m [27]. Other studies report the octane
number requirement decreased by 1.0 - 1.9 RON/300m without specifying
altitude [38]. Modern engine management systems can accommodate this
adjustment, and in some recent studies, the octane number requirement was
reduced by 0.2 - 0.5 (R+M)/2 per 300m increase in altitude.
The larger reduction on older engines was due to:-
- reduced air density provides lower combustion temperature and pressure.
- fuel is metered according to air volume, consequently as density decreases
the stoichiometry moves to rich, with a lower octane number requirement.
- manifold vacuum controlled spark advance, and reduced manifold vacuum
results in less spark advance."