David,
There are currently only *two grades of gasoline sold at
Pemex stations in Mexico--Regular in the green pump,
and Premium, in red pumps.  Diesel is commonly available also.
I haven't seen Nova at a Pemex station the past two years I've
been driving there.
I never heard pings or knocking with Regular Pemex, but my
van had an *alarming loss of power & seemed to sputter at times
using straight Regular Pemex.  The Premium Pemex seems to work
well in my '85 in all driving conditions.
Phaedra
'85 Westy Basecamp

----- Original Message -----
From: David Beierl <dbeierl@attglobal.net>
Subject: Re: Octane & Driving in Mexico

>Novas, is the lowest grade of gasoline and also the most common. It is
> >sold out of Blue dispensing pumps, and is popular with
> >Mexican drivers because of it's price (usually a few pennies less per
> >gallon than higher grades). Most heavily laden RV's cannot
> >use Nova, becuase it's octane level is far less than even the lowest
grade
> >of US gasoline, and it's use causes severe knocking
> >and piston damage. Contrary to popular opinion, Nova does not contain
> >significant amounts of tetraethyl-lead.
> >Environmental pressures in the USA caused the lead additive market to dry
> >up early in the 1980's, and subsequently, lead was
> >phased out of Nova gasoline in the late 1980's. I use Nova only when I
> >cannot avoid it. Curiously, running the fuel through a
> >engine does not produce immediate results. It's only after a hundred
miles
> >or so, that the full effects of it's low octane begins to
> >cause pre-ignition and detonation.
> >
> >MAGNA SIN
> >
> >This mid-grade fuel is sold from a bright green pump, and is Mexico's
most
> >popular unleaded gasoline. It's octane level is
> >somewhere around 86, and is superior to the silver pump "Extra" which it
> >replaced in 1990. Most vehicles will run acceptably on
> >"Magna" (as it's popularly called in Mexico). However, some very heavily
> >laden motor homes and tow vehicles can find
> >themselves in a position where Magna Sin, is just "border-line" in
> >preventing knocking and pinging. These vehicles will have to
> >have their ignition timing adjusted to prevent engine damage.
> >
> >PREMIUM
> >
> >Mexico's newest gasoline, is also it's best effort to date. Unfortunately
> >Premium gasoline is found only in larger towns and
> >cities, and will slowly migrate outwards to medium size towns. Premium
> >seems to have an octane rating that's higher than US
> >regular unleaded gasoline. The superiority in octane and performance over
> >Magna Sin, makes seeking out and filling your tank
> >with this fuel a wise choice, when availability permits. Premium is
> >unleaded, and like Nova, and Magna Sin,
> >Premium, does not seem to contain the Additive "MTBE" found in California
> >fuels.
>
>
> US gas is graded by an average of two octane numbers, as detailed in the
> following quote from http://www.off-road.com/rick/gas2/ -- the Research
> Number is the number used in Mexico (and in Europe), and the Motor number
> which is considerably lower is the number that was previously used in this
> country.  92 research octane (Mexico Magna Sin) is supposed to be
> ordinarily equivalent to 87 R+M octane, but if the M number were
> considerably lower this would change.  And the M number reflects
heavy-load
> conditions, such as a Vanagon in hot weather would experience.  This is
the
> best explanation I can come up with, as the official and quasi-official
and
> university sources uniformly say that Magna Sin is 92 R, or 87 (method
> unstated) -- while the off-road and RV people uniformly say it's less than
> US regular.
>
> >The number you see on the gas pump is supposed to tell the octane reading
> >of the gasoline. It's not quite as simple as that. Here's how it all adds
up.
> >
> >The Research, or "R" Method, of rating octane is done on a standard test
> >engine in a lab. The air temperature is controlled on this to a strict
125
> >degrees Fahrenheit. Mild loads are put on the engine, just about the
loads
> >you might put on your family car under normal driving conditions. This is
> >called an F1 test.
> >
> >The next rating test is called the Motor Method. Here, another engine is
> >used on a dyno, but the air is introduced into the inlet at a hot 300
> >degrees Fahrenheit. Heavy loads, similar to full-throttle acceleration
and
> >passing on uphills, are dialed into the engine. The engineer notes ping
> >and detonation at certain load conditions and the octane rating is
> >determined by its ability to control the detonation. This is called the
F2
> >test.
> >
> >The number you see on the face of your gas pump is known as the Road
> >Octane rating and is a combined average of the Motor and the Research
> >Methods. In fact, if you take a close look near the posted octane number,
> >you'll more than likely see: M0+R=92 OCTANE, or whatever the actual
octane
> >rating is of that particular gas. For example, if the F1 test showed 94
> >octane and the F2 test indicated 86, then the Road Octane rating would be
90.
>
> david
>
>
> At 11:12 PM 6/13/2001, PSavage wrote:
> >Volks,
> >For any of you planning to venture into Mexico--
> >I've found that, despite what it says at the Pemex
> >pump, my van will *not run well at all on Pemex regular.
> >So when in the higher altitudes I always use premium;
> >on the coast, away from grades, I can get away with
> >regular--but even then I often have to mix it 50/50.
> >
> >So consider yourselves warned...
> >Phaedra
>
> David Beierl - Providence, RI
>   http://pws.prserv.net/synergy/Vanagon/
> '84 Westy "Dutiful Passage"
> '85 GL "Poor Relation"
>