Re: [DML] Type of fuel to use

["A.H. MacIntosh & Co." <dmc12@xxxx>]

European octane is measured using a single system (motor octane, if I recall
right, but not sure) In the USA we use an averaged system... remember the
little sticker on the pump that says "R+M/2" In this system, both "motor"
octane rating, and "Research" octane are added together, and divided to
result in an average rating.

Octane rating says nothing about a fuel's purity, or quality, only it's
resistance to detonation. When an engine knocks, what is happening is that
the fuel is igniting from the heat of compression, and interior engine
temperature. (like a diesel... sort of...) Preigintion knocking can, and
will, eventually hammer even the best forged racing pistons to dust in the
end. It destroys the crystalline grain of the metal. The shocks also pound
the daylights out of the journals, pins, and connecting rods...

Diesel engines use extremely heavy reciprocating parts, and higher presure
oiling systems to prevent this damage... a gasoline engine doesn't

The "research" rating reflects the fuels performance at low, and moderate
engine loads, and speeds. On the other hand, the "motor" number reflects the
fuel's resistance to detonation under high engine speeds. It is possible to
have a fuel "knock" at a low speed, but still work well at high engine
speeds.

In any case, with the PRV's (in stock trim) rather anemic compression ratio,
I can't foresee needing any high octane rated fuel. Modern unleaded
"regular" works fine at 9:1... but if it makes you feel better to pay a few
$ more for premium... well.


> > Hi,
> >
> > I am a new prospective owner of a DeLorean, before I buy, I'm
> > gathering all info I can. One question comes to mind, I know the
> > manual and several sites say to use 91 Octane fuel, only thing close
> > to it is 93, and that does get expensive. Can 87 or 89 Octane be
> > used with no ill effects? I'm told how the Europeans and how the U.S.
> > rates gasoline are two different things, any truth to this?
> >
> > Thanks.