The truth about gasoline

[GMMerlin]

A number of myths about octane have grown over the
years. There is a widespread perception that the greater the
octane the better the performance. However, once enough
octane is supplied to prevent engine knock, there is little, if
any, performance improvement. One exception to this would
be in vehicles equipped with knock sensors. In these vehicles,
if octane is insufficient, the computer will retard the timing to
limit engine knock. If the vehicle is operating in the “knock
limiting” mode (retarded timing), using a higher octane fuel will
allow timing to be advanced, resulting in some level of
performance increase. However, even in these vehicles,
tests have shown that there is no perceptible performance
improvement from using a fuel of higher octane than that
recommended by the vehicle manufacturer.
Another myth is that using a higher octane fuel will result
in improved fuel economy (increased miles per gallon). Octane
is nothing more than a measure of anti-knock quality.
Fuel economy is determined by a number of variables including
the energy content of the fuel. Some premium grades of
fuel may contain components which increase energy content.
In those cases, fuel economy may improve slightly as a result
of higher energy content, but not as a result of the higher
octane. Two fuels of identical octane could have different
energy content due to compositional differences.
Consumers need only use a gasoline meeting the
vehicle manufacturer’s recommended octane levels. If engine
knocking occurs on such fuels and mechanical causes
have been eliminated, then the consumer should purchase
the next highest octane gasoline (above the manufacturer's
recommendation in the owners manual) that will provide
knock-free operation.
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[maxwedge]

GMMerlin, every driver everywhere should read/know this, good job, but I hope you didn't have to type all this. Before knock sensors,and with distributors, some performance gains were available by modifying advance curves to gain performance even in a lower compression engine, thats over!! As an " 0ld fart", did this for years.

[ScarabEpic22]

Thanks, now everybody should read this and understand what higher octane is really for!

[balboasdelight]

I agree that higher *octane* per se does not increase performance or otherwise benefit the engine. However, I believe there is more to "premium" grades of gasoline than just the octane. Quoting from the reference cited in this thread:

"Although not specifically included in ASTM standards, a variety of specially formulated additives are added to gasoline to enhance fuel quality and performance, and to maintain fuel standards during distribution. ... Benefits to the consumer are numerous and may include improved performance, increased engine life, lower deposits, driveability improvements, and better fuel economy. A good example of fuel quality improvement with such additives is the increase in usage of detergents and deposit control additives and the positive impact it has had in minimizing the incidence of port fuel injector fouling."

It is the higher level of additives (particularly detergents), not the higher octane level, that motivates me to run an occasional tankful of "premium" gas. I realize additive packages, including detergents, are available for the consumer to add to his own gas. However, I place greater faith in chemical expertise of, e.g., ExxonMobile's engineers than in my own, and it's just plain more convenient to push the expensive button on the fuel dispenser every now and again.

The underlying assumption here is that "premium" gas does indeed contain beneficial additives that "regular" grade gas does not (or contains more of them). The oil companies' advertising certainly implies that to be the case.

.

[Schurkey]

What hasn't been explicity stated--yet--is that there is no such thing as "gasoline".

That is, it's NOT a single chemical compound. What is SOLD as "gasoline" is a more-or-less random mixture of hydrocarbons (and additives--detergent and octane enhancers and "magic") that happened to be available at the refinery at the time. So, yeah, the viscosity is thin, and it's guaranteed to burn. Beyond that, there's no guarantee of heat content, and (VERY IMPORTANT) the octane rating at the pump is the AVERAGE OF TWO MEASURMENT METHODS: RESEARCH METHOD AND MOTOR METHOD. So a gasoline that does outstanding on the Motor octane test, but is weak when tested by the Research method could have the same rating as one that has a strong Research octane rating, but is weak in the Motor rating. They would NOT perform the same in your engine, but they'd have the same label at the pump.

GASOLINE IS A CRAPSHOOT. Good luck. We'll need it. I remember a few years ago there was a gasoline distributor on the east coast somewhere that was mixing "hazardous waste" into the gasoline. Figured that was a great way to get rid of it. (who knows, maybe he was right...)

[balboasdelight]

Originally Posted by Schurkey

What is SOLD as "gasoline" is a more-or-less random mixture of [stuff] that happened to be available at the refinery at the time.

There is certainly some variation in gasoline, but I doubt it's quite that random. From what I understand, the basic gas is the same stuff for everybody, and each distributor/retailer adds its own (proprietary) package of additives. Those, at least, I would expect to be fairly consistent (for the major brands; mom & pop outfits buy additive packages from the distributor (if at all), and those likely experience much greater variation). Unstabalized gasoline also goes "stale." So, while there's no guarantee, your best bet is to buy gas at a busy outlet of one of the major oil companies -- where the gas likely has more consistent additives and doesn't sit around in the tanks for a long time.

.

[Schurkey]

Originally Posted by balboasdelight

There is certainly some variation in gasoline, but I doubt it's quite that random.

I suspect you're right--at least most of the time. The one thing we have in our favor is that they make A LOT of it. Therefore, things tend to be somewhat standardized simply because they don't want to re-invent the process every day.

What I was trying to get across is that there aren't any guarantees of consistancy, there is no single magic formula to "make" gasoline. Because gasoline varies, and the posted octane rating method is less than optimum, I'll stand by my statement that "gasoline" is a crapshoot. Even buying the "correct" octane does not guarantee performance.

[jozuah]

Octane is the rating that describes the rate at which fuel burns.

the higher the octane the "slower" the burn. therefore if you have an"octane Ping" you raise the octane and slow the burn, alowing the piston to reach (X)degrees B.T.D.C. before the fuel/air mixture starts to burn, eliminating the "ping" otherwise known as Pre-ignition of the fuel-air mixture hitting the top of the piston on the upward travel of the compression stroke. If you use a fuel that has a higher octane rating than your owners manual recomends, (providing your vehicle is ECM equipped with a knock sensor)you are forcing your engine to burn fuel slower/advance timing.
Example:
87 octane fuel burns at 12 B.T.D.C. no ping/pre-ignition <-- owners manual recomends.
90 octane fuel burns at 6 B.T.D.C. still no ping.. ECM advances timing to compensate for slower burn.
the result is a vehicle that does not burn fuel as efficiantly as as a vehicle that uses 87 octane fuel therfore wasting money at the pump.



***disclaimer***
im new to this board, therefore i am just inserting my 2 cents to possibly further explain the AWSOME post above, and not to "flame" anyone.
that said, i will say hello to all of you now,,,,

Hello all

Joz

[Kornfused]

What do you think about additives such as Gumout or Sea Foam? I have a 99' Silverado and have had to have my mechanic clean out carbon deposits form the manifold. I am not familar with fuel injection lie I used to be with carburators. Alos, we used to put a little oil in the gas to keep the diaphragms and such from drying out - I do not even know if such a thing exists in fuel injection. What are your thoughts?

[juventus1983]

so why do performance cars specify premium?

[maxwedge]

Welcome to AF. The usual higher compression associated with high performance engines require additional octane to maintain optimal timing curves.

[Thundare]

Cars aside,

high octain fuel really works in my QUAD

[Jethro]

Higher octane fuel burns cooler which is important on high perfomance engines.

[michael sinkoski]

exxons engineers, really, they let them prepare press releases? More detergents? I don't know but 87 octane is an exceptional solvent with virtually no residue after combustion. I think may be you justify the increased price with a better product. Perhaps you should run aviation 100 low lead fuel, your car will become a space shuttle, or the catalytic converter will be ruined in about 15 minutes. Don't be suckered by gas corporations, they are selling to whoever will buy

[Schurkey]

I've been away from this post for too long.

Originally Posted by jozuah

Octane is the rating that describes the rate at which fuel burns.

the higher the octane the "slower" the burn.

Not exactly. Flame speed depends on many factors including but not limited to pressure and turbulence inside the combustion chamber.

What "octane" refers to is the fuel's ability to resist spontaneous combustion (detonation.)

Originally Posted by juventus1983

so why do performance cars specify premium?

Originally Posted by maxwedge

The usual higher compression associated with high performance engines require additional octane to maintain optimal timing curves.

Yup. Higher compression ratio--and greater throttle opening--both tend to increase cylinder pressure--and increased cylinder pressure leads to detonation if the fuel isn't suited to the pressure generated.

Originally Posted by Jethro

Higher octane fuel burns cooler which is important on high perfomance engines.

Not exactly. BTU (heat) content of the fuel can vary with the chemical make-up of the "gasoline"; it's not a direct relationship with octane number as posted on the pump--although I suppose different octane improvers could affect the BTU content in the same way that selecting a different hydrocarbon compound could affect the BTU content of the finished product. Since it's the heat that does the work in the engine, more heat content is desirable.

http://en.wikipedia.org/wiki/Octane_rating

As far as "detergent" and "cleaning power", what you need is not "premium" gasoline (as in high-octane)--what you're looking for is "Top Tier" gasoline. "Top Tier" gasoline and "premium" gasoline are describing different characteristics. Of course, you could certainly use Top Tier Premium gasoline if you wanted to.

http://en.wikipedia.org/wiki/Top_Tie...rgent_Gasoline