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My brand preferences (highest to lowest; I have no "tier 3"):
COLO: Conoco, Texaco or Amoco (91 octane)
OTHER: Shell, Chevron, Amoco/Texaco, Philips66 (generally 93 octane)
(after that, either it's a brand I've heard of or it's not; I'll usually
choose the one I've heard of, but not always; it's as Pete said, all the
similar gas sold in stations in a remote location almost certainly came out
of the same distributor's tank. (Each one adds their own fuel additives,
which can be different, but perhaps the most important additive is the dye
they can potentially later use to refute a claim that their gas caused
some kind of damage!)
I prefer gas with good cleaning properties (not just injectors, but intake
tract too); this is what seems to keep my engine happy over the long term.
But I always treat my car's fuel with DurAlt Fuel Conditioner (1 oz per
16 gallons or so), which makes any gas work better (partly by altering fuel
properties, partly by keeping the engine cleanest).
Sunoco 94 sucks; I'll put in up to 8 gallons in my tank, but only to get
their oil change discount coupon before having Mom's car's oil changed
there; otherwise I avoid it.
I cannot recall having heard of Sunoco 93 in recent years, though. But
octane ratings do vary by some regions, and also over time...
I've come to prefer Shell when I'm in the low country, but that was based
upon Shell's inclusion of just "a smidge" of MTBE in their 93-octane blend.
But I only visit there, I don't live there, so I'm not sure Shell is really
that good at keeping intake bits clean long-term, but it's not like Sun94,
where the engine performance can go downhill after 1 tankful, either.
No don't get me wrong, I've been fighting against MTBE in gas for 13 years.
It's a poison. In an odd way, I'm glad it's finally been noticed in
drinking water -- no one but me seemed to mind breathing the poison, but
everyone seems upset if they're forced to drink it! (Congress effectively
shut down a major portion of the govt for a year over a blow job, but has
not found time to rewrite the laws that practically required MTBE; good to
know they always make time for the important things...)
So as MTBE [very] slowly disppears from this nation's fuel supply, maybe
Shell is the same as the others. But "a smidge" of MTBE is really good for
crisp performance, esp. in most turbocharged engines. OTOH, MTBE has a
significantly lower energy content than gasoline (so does ethanol, for that
matter); so-called "oxygenated" ("reformulated", too, I believe) gasolines
have a significant percentage of such oxygenates, leaving each gallon with
less chemical potential energy. (If you put more oxygen in your gas tank,
there's less room for fuel there...)
Fortunately, most oxyfuels are easily detected with one's nose. Especially
MTBE. I generally put a small squirt in my tank and then give the nozzle
a careful whiff (the fuel left in the nozzle from previous use may have
been there so long that the MTBE is long gone even though gas remains).
If it has lots of MTBE in it, I might, depending upon circumstances, move
on rather than fill up there. In winter here, I drive to the next county
to fill up.
Those "unbranded" (3rd tier) stations often compete on price and not with
other brands. One 'good' way for them to do this is (I've seen this in CA,
but it's been a few years...) is to use a lot of ethanol (in place of other
stuff) to raise the octane rating (particularly in their hi-octane blend).
The govt subsidy (tax break?) on the ethanol permits them to sell theirs
for $0.10 or $0.20 less than other brands. But, again, each gallon of
theirs contains less energy. (which means refilling more often, which
means pushing more fumes into the atmosphere if/where pumps have no
fume-sucking capability)
One problem this leads to has to do with fuel injector timing/capacity.
At high rpms, where max power is made, things happen pretty quickly...
There is an ideal window in time during each cylinder's intake stroke to
inject the fuel. But if the fuel is part oxygen, more of it is required
to properly mix with the air being ingested. But the only way to do that
(in most engines) is to leave the the injectors open longer. But then you
have fuel being injected at times that are less than optimal.
Also, even emissions-controlled engines do not burn stoiciometrically at
WOT. They burn a little extra fuel (ie, they burn rich), mainly to help
keep temperatures down (ie, don't want to melt those spark plug electrodes
[or anything else, incl oxygen sensor(s)!] too much/quickly. In this mode,
there is no "closed feedback loop" involving the oxygen sensors, ECU and
fuel injectors. This fuel-burning strategy will be affected somewhat if
the fuel isn't as rich as expected or needed. Hopefully the lower energy
content will result in lower power output and accompanying lower heat
production, but that's not necessarily so; the fuel could burn hotter
(extra oxygen) even as power output is lower. While this is not enough
to melt one's engine, the tendency is there; spark plugs and oxygen sensors
would probably feel it most. This is a case where I definitely feel better
knowing I have an extra margin of safety in the form of DurAlt, which
lowers exhaust port temperatures by helping combustion be more complete
before the exhaust valve opens; this permits more of the fuel's energy to
be put to work pushing down the piston, and less to escape as heat waste.
Oxyfuel is an oxymoron.*
- Dave; '95 854T, 101K mi
* except on rockets, spaceships and submarines
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