I uses Amoco for my premium fillups of my van, exclusively. Why?
Because it contains MORE detergents than the government regulates. It
is cheaper than a fuel additive when you take into count that my van's
tank is 37 gallons. All premium gas does not have extra cleaners, but
Amoco does, which is why I use it. I do not get any better mileage in
the van, nor do I see increased power, but it does run smoother for the
next couple months.
Note, you WILL have less power on regular than premium (In a high
compression engine that requires 91 octane). The Knock sensor retards
the timing, which causes the "maximum gas expansion" to happen when the
piston is farthur aling in it's down stroke. This reduces the peak
cylinder pressure. It eliminates the knock, but WILL reduce power and
and give you poorer mileage. Drop the compression level of a engine
from, say 9.5:1 to 8.5:1 to compensate for the lower octane gas, and
you will drop HP.