Re: Anyone with High Octane Gas BTDT's?

[Scott Fisher <sefisher@cisco.com>]

AQUATTRO4U@aol.com wrote:
> 
> Hey everyone,
> 
> I'm looking for BTDT's on high octane gas.

By way of credentials, I'll show you my burned/broken piston from trying
to run an 11.5:1 cylinder head on 92 octane gas.  (I *did* win the drag
race with a BMW M5, though... in a 1963 MGB, no less.  But it was an
expensive victory...)

Basically: any octane *higher* than what your car is designed for is a
waste of money, but generally harmless.  The exception is when/if you
modify your car in such a way that it can take advantage of the extra
octane.

Octane is actually the name of a molecule; I think it's got 8 benzene
rings, hence the "oct-" part of the name, but oil-company chemists on
the list are invited to educate me if I'm mistaken.  Whatever its
chemical construction, it has become a more or less generic term for
"octane rating," which really implies a gasoline's resistance to
preignition.

Today, gas companies measure a gasoline's "octane rating" by using a
neat little single-cylinder test engine that has a variable compression
ratio.  They run the engine at varying compression ratios till they find
the one at which the gasoline does not preignite; the higher the ratio
at which that happens, the higher the octane rating.  It may or may not
actually have anything to do with how many molecules of gas there are
with 8 benzene rings; it is entirely related to the gasoline's
properties of ignition and preignition.

Ignition is supposed to be a smooth propagation of the flame front,
starting at the spark plug and ending with the piston all the way down
in the cylinder bore.  Preignition occurs when, for some reason, the
gasoline lights off before the spark plug sets it off, usually in a
sharp, spike-shaped tongue of flame that looks and acts like a cutting
torch.  Preignition is actually an explosion, as opposed to smooth (if
fast) combustion; preignition can cause not only intense heat, but also
shock waves (which I'm sure is why I broke the top off that piston).  In
short, it's a very bad thing.

The conditions that affect preignition are:

1.  Static compression ratio (as in my holed-piston example).  That's
the ratio between how much room is in the cylinder bore with the piston
all the way down, versus how much is in the bore with the piston all the
way up.  For instance, in the ex-race motor that I blew up dragging with
the M5, the ratio was 11.5 to 1 -- meaning that the full cylinder
volume, with the piston all the way at the bottom, was 11.5 times as
large as the volume with the piston all the way at the top.  Most modern
street-driven cars are designed with ratios below 10:1, but modern
electronics and metallurgy have made a huge difference in what's
acceptable, because the electronics can alter most of the other
conditions dynamically.

2.  Ignition timing.  If the ignition timing is too much advanced (that
is, if the spark plug fires too early in the cycle), the flame front
starts to spread while the piston is still moving up.  A little of this
is good, particularly for operation at high RPM, because there's less
time between all-the-way-down and all-the-way-up as the engine runs
faster; a lot of advance can mean that you develop uncontrolled
combustion in the middle of the cycle, and you can blow holes in the
piston that way too.

3.  Temperature.  Obviously, gasoline will burn if you get it hot
enough; that's the whole POINT, isn't it?  Sometimes, whether due to
engine design, deposits in the head, or other reasons, something in the
cylinder can cause the gasoline to ignite before the plug goes off. 
However, to an extent, you want the engine to run hot and the intake
charge to run cool; that's why cars have radiators and turbo cars have
intercoolers, to adjust the temperature for maximum efficiency.

4.  Turbocharger boost (where applicable).  The turbocharger basically
increases #1 and #3 -- that is, it increases the pressure differential
between the piston at the bottom and piston at the top, *and* it
increases the temperature in the cylinder.  Done well, this is a good
thing; done poorly, it results in very expensive grenades (as in the
things you hear racers say, such as "Waal, Jim, my internal combustion
engine became an external combustion engine somewhere near the exit of
Turn 3; apart from that, the KY Personal Lubricant/First Response
Pregnancy Test Special ran great all day, my crew did a fantastic job,
and we'll be back for Pocono next weekend").

5.  Fuel mixture.  The rules of thumb are that 14.3 pounds (mass, not
volume) of air are required to burn 1 pound (mass, not volume) of
gasoline.  That ratio is called stoichiometric.  In general, if you run
leaner (more air, less gas), your engine will run hotter, and heat (see
#3) makes a car preignite; conversely, extra heat can make a little more
power and of course makes a pound of gas go a little bit farther,
something most automakers are still working on.  But to do that, you
have to tweak variables 1 through 4 so that you don't get preignition. 

(Note: for racing engines, as a VERY broad rule of thumb, maximum power
occurs at a/f ratios of about 12.5:1, which is why you sometimes see
huge roostertails of flame coming out the tailpipe; this is because
there is still unburned fuel left after the combustion of all the air in
the cylinder is complete.  I sometimes ask people to look at an engine
as though it's a device for burning air, using gasoline to ignite it;
it's not entirely accurate, but it's very enlightening especially if
you're considering making serious modifications to the engine's hard
parts -- camshafts, port shapes, valves, etc.)

Here's the thing: most modern cars, even turbo cars, are designed to run
on whatever the manual says.  Let's say that is 89 octane.  This would
mean that if you put 87 octane into it, it'll knock; if you put 92
octane in, it'll run smoothly.  That's the default condition for which
the engine electronics are all calibrated; air/fuel, timing,
temperature, and knock sensors all expect the flame propagation
characteristics of 89 octane.  And because the compression ratio,
ignition timing, and engine electronics are designed to make it run
optimally at 89 octane, you'll get NO MORE PERFORMANCE out of 92
octane.  You'll just spend more money.

The reason I put that BUT in all-caps, however, is that a huge industry
has developed lately (well, apart from the one that's existed since the
first time some guy went for a ride in his buddy's car and said, "I bet
I can make this sumbitch HUM") in making cars run faster than the
factory intended.  This has come about because modern carmakers (since
the early 1980s) have learned to control almost everything except static
compression ratio with electronics.  This lets them actually measure
what's going on in the engine -- temperature, unburned fuel in the
exhaust, timing, even the specific vibration characteristics that
indicates preignition -- and adjust it accordingly, dynamically, while
the car is in motion.

Modern carmakers, even Audi, build their control systems on the
assumption that you're going to run with whatever octane rating they put
in the manual; modern carmakers, especially including Audi, sometimes
expect that you won't even READ the manual (especially the part that
says this is the brake and this is the gas, and don't step on the GAS
instead of the BRAKE if Mike Wallace is around, please).  And, to a very
large extent, running higher octane gets you nothing but poor --
*unless* you've modified something in the car.  (Even in cars with
adaptive electronics, there's usually a limit at which the standard
fuel-air maps, timing curves, etc. stop, a sort of fail-safe designed to
keep the warranty in effect.  Those limits are part of what a
reprogrammed chip is designed to tweak, and what is meant by an engine's
electronics "learning" new settings.)

For example, you might tweak the distributor and run more spark
advance.  This helps bump up power in the midrange because the
compression cycle occurs that much more quickly when the engine's
turning faster.  The risk is that with lower octane gas, the advanced
timing can cause preignition because you've changed one of the 5
variables.  So now you NEED a higher octane gas than the factory
specified, to avoid preignition.

Or you can run a different mixture, richer or leaner, depending on what
testing says will move you in the direction of more power.  More power
brings with it more heat, which can lead to preignition.  So now you
NEED a higher octane gas than the factory specified, to avoid
preignition.

Or you can increase the turbo boost, which a) increases your effective
compression ratio and b) increases your combustion temperature and c)
increases the amount of air in the mix, effectively d) leaning the
mixture.  It doesn't *directly* affect your timing, but it changes the
*requirements* of ignition timing.  So now you REALLY NEED a higher
octane gas than the factory specified, to avoid preignition.

Getting the idea?  Now, I've told you all THAT so you'll be able to make
sense out of my specific responses...

> In the San Francisco Area Supreme is 92 octane.

It's also typically "enhanced" with MTBE, methyl tertiary butylated
ether, which is Seriously Bad Juju and a mark of corruption in
California state government.  But that's another story.  Short answer
(and aren't you glad this isn't the LONG one?): MTBE is a toxic,
hazardous by-product of the refining process that oil refineries used to
have to pay huge amounts to dispose of safely.  Then they lobbied the
California legislature, which passed a law saying that it was an
"oxygenator."  This meant they could add it to gasoline during the
winter months (originally; later to certain counties year-round) to help
reduce ozone production (something that ethanol does quite effectively,
BTW).  They then raised the price of gasoline because it had an
oxygenator in it -- completely obscuring the fact that this oxygenator
used to be toxic waste that they had to pay to get rid of safely.  Oh,
it also turns out that MTBE eats rubber components of fuel systems, but
the 200% and up increase in engine fires in counties that use
MTBE-enhanced gasoline are purely coincidental, pay no attention to that
man behind the curtain.  And it leaches out into groundwater, and it's a
carcinogen, which means we have to ban powerboats from rivers and lakes,
because this carcinogen (which it now turns out isn't cleaning up the
air all that well either) eats fuel systems and then leaks into the
waterways.  At times like this, armed insurrection seems almost
reasonable... 

Note: Chevron gasoline stations, and a growing number of Union 76
stations, do NOT use MTBE -- they oxygenate their fuel with ethanol. 
No, I don't work for either company, I just try to buy their stuff.

> I talked to a local independent gas station and asked him if he new where I
> could get some high octane unleaded gas.
> 
> He told me if I buy some he would stock it in one of his pumps,
> 
> It's supposed to be 104 octane Unleaded.

You can also get it at the many fine Bay Area racetracks, where it costs
about $4-$5 per gallon.  About what Phil pays for four-star premium
every day, inotherwords...

> I did mention to him I had friends that might buy some too.
> 
> The service station is in San Mateo CA and it's called "Bob Reed's"
> 
> It's an Olympic gas station  (How appropriate for our "Olympic" cars)

Olympic is, at times, an iffy brand because as a small retail-only
chain, they buy for price, from various refiners.  We've got one close
to home, and the prices are good, but I like it when my cars start and
don't catch fire.  So I run Union 76 or Chevron in the Audi and the
Alfa.  The Olympic works fine, however, in my wife's '63 Volvo, with its
tired rings and valves and a current effective compression of about 100
psi per cylinder.  

> It's located on Palm Avenue in San Mateo by the super Safeway near 20th & El
> Camino
> 
> So here's my questions?
> 
> How much octane can I put in the car without hurting anything?

As much as you want.  Or rather, as high an octane rating as you want;
you're unlikely to get pure eight-ring molecules, for instance.  The
only thing you'll hurt will be your wallet.

> Will I notice a difference in the way my car runs?

Almost certainly not, with two big UNLESSes:

Unless 1) you have modified the chip, turbo, or other characteristics as
described above, OR

Unless 2) you are experiencing knocking, pinging, detonation,
preignition, hesitation or bad running at present on 92 octane gas, and
none of those symptoms are attributable to some other mechanical or
electrical fault in your car.  (What?  An ELECTRICAL FAULT in an Audi? 
Oh, the humanity!)

> Should I do a mixture like 50/50 of 92 and 104 octane?

You can; the question remains whether you need to.

> Is there a math formula for the mixtures so I can determine what octane level
> it will be if I mix it with 92 octane?

For your purposes, it's roughly linear -- that is, x gal at 92 + x gal
at 104 = about 2x gallons at 98 octane.  And unless you've modified your
chip, turbo, etc., probably about 6 octane points higher than you need.

> Anyone ever used low lead AV gas?

Nope, but race pals/antique-car owning friends have.  General consensus
is that avgas has additives which are really designed for aviation
operation (and here they lost me citing Reid vapor pressure ratings and
the like).  It's not the best thing for extended automotive use.

> If so how'd it work and did it destroy your kitty?

If it has lead in it, it WILL kill Fluffy eventually.  Most aircraft
engines are designed these days for unleaded, though; lead used to be a
valve-seat lubricant, but that's another overly-long posting.

My recommendation: go to the autoteller and take out three yuppie food
coupons ($60), go to Laguna Seca some day (call ahead first to make sure
the guy with the key will be there), and fill 'er up with 104 octane gas
from the pumps on the track.  Then drive around like mad and see if it
really makes a difference.  (Or better yet, have your wife go fill it up
*without telling you* and see if you notice a difference.)  On a typical
Audi, it's going to run you about $60 a tank.

> Also any other information you think I ought to know?

I guess so... :-)  It's a little long, but the money you'll save by not
wasting it on excessive octane should more than pay for the extra
connect time spent downloading it.

--Scott Fisher 
  Sunnyvale, California