Hello Lawrie,
I appreciate the sharing of your knowledge, and as always
default to your expertise. I do believe the
question presented by Bob Donahue was not about KTs or
modified engines, but was as follows:
>"I use premium in all my cars, even my TD. Even though the
TD doesn't need it, I figure the extra octane is a hedge
against pre-ignition in the event the engine overheats or
the timing gets out of whack. Does this make sense, or am I
being stupid?"<
I would like to share what the FTC has to say:
"http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm";
>"Are you tempted to buy a high octane gasoline for your
car because you want to improve its performance? If so,
take note: the recommended gasoline for most cars is
regular octane. In fact, in most cases, using a higher
octane gasoline than your owners manual recommends offers
absolutely no benefit. It wont make your car perform
better, go faster, get better mileage or run cleaner. Your
best bet: listen to your owners manual. The only time you
might need to switch to a higher octane level is if your
car engine knocks when you use the recommended fuel. This
happens to a small percentage of cars. Unless your engine
is knocking, buying higher octane gasoline is a waste of
money, too. Premium gas costs 15 to 20 cents per gallon
more than regular. That can add up to $100 or more a year
in extra costs. Studies indicate that altogether, drivers
may be spending hundreds of millions of dollars each year
for higher octane gas than they need."
I would also like to submit an article by Tim Wusz of Union
76 Products Company:
>"Octane numbers can be very confusing due to several
different terminology's used in discussions. I will try to
clear up some common misunderstandings and define some of
the various terms used when discussing octane quality.
Octane The octane quality of a gasoline is its ability to
resist detonation, a form of abnormal combustion.
Detonation occurs when the air-fuel mixture reaches a
temperature and/or pressure at which it can no longer keep
from self igniting. Two types of abnormal combustion are
common: the first is detonation as previously mentioned and
the other is preignition. Detonation occurs after the spark
plug has ignited the air-fuel mixture and the flame front
is moving smoothly across the combustion chamber. If,
during this burning process, the unburned air-fuel mixture
reaches a temperature and/or pressure at which it is no
longer stable, it burns very rapidly causing a new flame
front to collide with the one that originated at the spark
plug. Maximum pressure in the cylinder occurs before the
piston reaches top dead center (TDC) and that pressure
try's to push the piston down before it is ready to go
down. Piston burning and rod bearing damage are the result.
Preignition is the other bad actor and is usually started
by a hot spot in the combustion chamber which causes the
mixture to ignite before the plug fires. Under wide open
throttle conditions, preignition will destroy pistons in
seconds. Research Octane Number (RON) RON is determined in
a single cylinder variable compression ratio engine that
operates at 600 rpm with a 125 degree inlet air temperature
at standard barometric pressure. Spark advance is fixed at
13 degrees btdc. In a real world engine, RON is necessary
to satisfy part throttle knock problems. A good quality
racing gasoline has a RON in the range of 110 to 115. The
difference in the spread of RON is not very important to
racing engines. The test and hardware were originally
developed in 1931. The hardware was revised in 1946 with
procedural changes made until the late 1960's. Motor Octane
Number (MON) MON is determined in a single cylinder engine
similar to the RON engine with a few changes that make
operating conditions more severe and therefore the octane
numbers are lower. The MON engine runs at 900 rpm with a
300 degree mixture temperature. Spark advance varies with
compression ratio. In a real world engine, MON is necessary
to satisfy octane demands at wide open throttle. This is a
very important number for racing engines since they spend a
high percentage of their lives under high speed and high
load conditions. Racing engines cannot afford to be short
on octane quality, since detonation or preignition will
quickly reduce a racing engine to junk. The motor octane
appetite of an engine with 13:1 compression ratio and a
four inch bore varies with operating conditions but is
normally around 101. Good quality racing gasolines have MON
in the range of 100 to 115. If your engine requires a 101
MON, it is of no value to use a gasoline that has a 115
MON. To cover yourself for extreme conditions, it is wise
to have an octane cushion but there is no advantage to
using a very high octane quality product if you do not need
it. The MON test was originally developed in 1932. Major
hardware changes were made in 1948 with procedural changes
made until the late 1960's. (R+M)/2 This is the average of
RON and MON. It is sometimes referred to as the aki or
anti-knock index. By law this number must be posted on the
dispensing pump at retail outlets in most states. It is the
most commonly used octane reference today. It was developed
about 20 years ago as a compromise between RON and MON for
advertising purposes and also to keep from confusing the
consumer with too many different terms. It has erroneously
been referred to as road octane number. Observed Road
Octane Number (RdON) This is derived from testing gasolines
in real world multi-cylinder engines, normally at wide open
throttle. It was developed about 70 years ago but is still
reliable today because engines are the test tools so we are
able to take immediate advantage of current technology. The
original testing was done in cars on the road but as
technology developed the testing was moved to chassis
dynamometers. this eliminated a lot of variables and some
people have since built very elaborate chassis dynamometers
with environmental controls to improve consistency. "76"
has modified this test additionally to use it with racing
engines on engine dynamometers. This has given us the
opportunity to evaluate gasoline blends during our racing
gasoline development that had good RON and MON but that did
not respond well in the racing engine under a full throttle
excursion through the entire rpm range. We felt these
conditions were the true indication of how the fuel could
be best developed. In our program we found that the
blending components and their ratios are far more important
to the racing engine response than high RON and MON numbers
found from testing the gasolines in 40 year old single
cylinder laboratory engines with antiquated combustion
chamber designs. RON and MON can only be used as a guide,
the final word must come from the road octane number. As an
example, 76's current 108 octane leaded racing gasoline
blend is the result of testing over 100 experimental
blends. The final blend has a road octane number (RdON) of
110, the same RdON as one of our competitors gasoline that
has advertised 116 RON and 116 MON. Using only RON and MON
can lure a person into a false sense of security. If you
want to be certain that your racing gasoline has been
thoroughly tested in real world racing engines with the
horsepower and road octane number maximized, choose "76"
for your engine. If you want high RON and MON without
knowing how it will work in your racing engine, buy from
the other guys.
I don't know why the racers of yester-year would "shave"
the deck height to the point of making the cylinder head
non serviceable. I guess a tank full of moth balls and a
high compression ratio was the cheap ticket for speed.
I know when I was a lad, there was no substitute for cubic
inches.
Best Regards;
Walton Smith
Yahoo! Health - your guide to health and wellness
http://health.yahoo.com
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