Editor's Note: Tom originally published this article to the members of the VetteNet mailing group. It is reprinted in the YL yankeelady with Tom's permission.
Someone in the octane thread asked for a chemist's view on the subject, so here's mine. However, first a view necessities and background:
Credentials: Ph.D. Organic chemist, 21 years as a practising chemist, 28 US patents (many on gasoline additves), work for a major oil company that is a leading (by volume) retailer of gasoline in the world. I've had engine tests (meaning an engine on a fixed engine stand run by a computer) and road tests (meaning cars driven by humans -- some on a course, some not) run on gasoline additives I've invented (while employed at the oil company). These additives have been tested in the US, England, and France under a variety of conditions. Many of my additives have also been tested in the BMW test (10,000 miles). I'm still employed by said oil company.
Disclaimers: The views expressed here are my own and not the company I work for (which is why I don't mention the company, although I realize any enterprising person could easily find out).
Copyright: This entire note is copyrighted by the author. Participants in this mail group (the VetteNet) may store and make one copy for their own use. Participants may refer to, copy, send, and re-send to particpants of this mail group and post or re-post sections of this note as long as this copyright notice is attached. Except for these specific exceptions, this note may not be copied, quoted, or transmitted in any form for profit or non-profit, or used for any type of publication without written permission from the author.
Corvette: Mine is a 1979 that is on its second trip through the odometer (and its second engine, and third interior). I've owned it approximately 12 years, love it, and may never get rid of it.
Octane:
I've seen many consummer magazines tell their readers that they are wasting money to buy a
higher octane gasoline if their car doesn't knock. If octane were not related to any other
feature of the gasoline, I would agree. However, how companies get higher octane gasoline
does make it different than regular and mid-grade gasoline. So the question to me then is,
do these differences make a difference? The short answer is what do I use, and I use
regular in all my cars and my truck. I use premium in my Corvette. Why? Because as any
Corvette enthusiast (to separate us from people who merely own one -- no flames, please)
knows, a Corvette is not a car, it's an experience. If you want to know the long answer
keep reading.
Base gasoline:
Crude oil differs depending on where it's from, and consequently, what comes out of it
when it's refined also differs. There are books on the subject and I can't possibly do the
subject justice here. As the oil differs, what is available for blending and cutting is
different. In the end, however, the refiner has to make economic choices, based on what's
available to him from the oil he is refining, on how to get the required octane to sell
(as well as meet MANY other criteria that make gasoline, gasoline -- again I can't do
justice to it here). What I generally (but not exclusively) see is that BASE (no additve
added to it -- you can't buy this, it isn't offered for sale) premium gasoline leaves less
deposits behind than other grades. There are certain types of molecules in regular and
mid-grade BASE gasolines that simply do not exist in premium gasoline that cause much of
this. Additives (see definition below) are added to the gasoline to help get rid of these
deposits, and modern additives do a marvelous job of this. What you buy is additized
gasoline.
Blending
components vs additives: MTBE (methyl tertiary butyl ether -- this is ether) and
ethanol are blending components, not additives. However, you'll see them called additives
in many places by many people. Blending components are part of base gasoline. The simplest
differentiation between an additve and a blending component is that the former are added
in ppm (parts-per-million) levels; whereas, the latter are added in percentage quantities.
Brand of
gasoline: Some of you probably know this, others may be shocked by it. Oil
companies swap base gasoline all the time. Let's say I have a refinery in Houston and you
have one in Dallas. It makes little sense for me to truck my Houston gasoline to Dallas
and for you to truck your gasoline from Dallas to Houston when gasoline is a commodity
product. So, I let you draw 100,000 gallons of base gasoline from my storage tank in
Houston for your Houston gas stations, and you let me draw 100,000 gallons of base
gasoline from your Dallas holding tanks for my Dallas gas stations. That way, we both save
on shipping. Yup, Texaco gasoline may have come from a Shell refinery and vice-versa. At a
gasoline terminal you may see trucks from up to six different companies all loading at the
SAME terminal (that for example may be supplied exclusively by Shell). What comes next,
however, is what makes Texaco Texaco and Shell Shell. Additive. Each company has its own
additive and adds it to the base gasoline. So while the base gasoline may be the same, the
additive is different, and hence the brand of gasoline you use is different because of the
additive, not the base gasoline.
Which additive
is better?: Given the above discourse, it's obvious that we all want the gasoline
with the best additive. Unfortunately, it's not that simple. Additves respond differently
in different base gasolines (even of the same grade). Also, some additves work better with
gasolines used in a carbureted car vs one that uses fuel injection. On a practical level,
additives are going to be developed today for today's cars -- meaning fuel injected cars.
For Corvette owners who have carbureted Vettes (like me), this is unfortunate. Carbureted
engines leave a LOT more deposits behind than fuel injected cars. From a regulatory stand
point, California was the first to call for all gasolines to pass the BMW test
(port-fuel-injected engine) in all grades of gasoline. Like all regulations, this one had
various massages put to it, but the net effect was that all oil companies went to work
developing additives that are a LOT better today than 10 years ago AND they are used in
all grades (not just premium -- hence the argument to use premium to get a better additive
went out the window).
Insider's trick
on gasoline additives: No matter what you do or what you drive, this trick will
help you keep down deposits inside your engine. You see, additives themselves will make
deposits and/or create a deposit that is different from the one made by base gasoline
alone. If you think about this for a moment, you'll come to realize that your engine will
build some kind of deposit based upon what additive you are using. Yes, it will build at a
slower rate, but it will build deposits. At some level this will taper off (but this is
maximum deposits and what Corvette owner wants that!). So what do you do? Simple, switch
to a different brand of gasoline (this will almost assure you of getting a different
additive but not always. Some companies buy additives from other companies, so it could be
the same. More on this later). What this will do, is the new additve will look at the
deposit formed from the old additive as foreign and begin removing it. Now after 5000
miles, you'll be rid of this deposit but you'll have a new one from your most recent
additive, so switch back and start the process all over again. As an analogy, this is like
building an immune response to an anti-biotic, so your doctor gives you a new one. I know
of absolutely no additive that will work as well as switching back and forth between
additives. On a molecular level this makes perfect sense.
So what's a
Vette owner to do?:
Hope this clarifies some points.
Copyright 1996 Barbara Spear
