MG Car Club of South Australia
MGC NEWS
MGC conversations with Richard Mixture, April 2018
Fuel for the Fire
ello again, it’s Richard here with a
remapping story. Remapping? I
always thought that remapping was
when you go into the newsagent and
buy the latest Gregory’s street directory.
But it’s got something to do with com-
puters evidently. Russell would know all
about it ...err... that is if he’s not out-of-
date already after six months of retire-
ment.
H
How many MGCs out there have com-
puter, measuring all sorts of things and
then adjusting the fuel, air and timing.
I’d say the number is a round one and
equal to the number of MGs made by
Austin.
Re-graphing is the term or
changing the advance curve as I was
told many years ago.
Now, the spark plug in each cylinder has
to light up at the right time to send the
piston back down the bore and turn the
crank etc, all the way to the back
wheels, no matter what speed the crank
is turning. So how do modern fuels,
namely unleaded fuels, work in our old
cars?
Once upon a time petrol was petrol and
then some smart spark found that in-
creasing compression ratios increased
performance but that lead to pre-ignition
or knocking or pinging. Petrol compa-
nies discovered that if they add lead to
the fuel mix it not only reduce pinging by
increasing the octane rating but also
reduced the wear of the valves and their
seats. In fact, when Curly was a lad,
ESSO found that tetra-ethyl lead (TEL)
worked wonderfully well and introduced
it to their fuel in 1927. TEL worked so
well it became an industry norm.
When TEL is burnt it forms a fine sus-
20
pension of lead salts that is largely lead
bromide which was the white deposits
on the inside of your exhaust in the old
days. This cloud of particles slows the
flame front down in the combustion
chamber, (this doesn’t happen with
unleaded fuel).
So jump forward into the 1960s and
some health professionals found that
people who lived on busy roads were
suffering from lead poisoning. Now I
wonder where that came from? It was
well known that petrol was not particu-
larly nice stuff, think fire, and when I was
a youngster washing up parts in petrol
was the norm, you just sloshed it all
about. While it wasn’t a good idea then,
it’s worse now with modern fuels con-
taining benzene which is a known car-
cinogen. Authorities started reducing
lead in fuel by the mid 1970s in the USA
and it was banned in Australia in 1985.
So the point of all this pre-waffle is that
our old lumps of ‘Best British Cast Iron’
as Bruce calls it, were designed for
leaded fuels which are unavailable these
days. So before you start brewing your
own fuels try retarding your ignition tim-
ing a little and winding your jets down a
little to make a slightly rich mixture when
compared to the settings written in the
manual!
I have played around with my SUs but
could never get the old cast iron lump to
run sweetly throughout the rev range. I
spent money and had a well known
dyno-tune business arrive at nothing
better than what I had achieved. In fact
I had to re-tune the mixture because
living in the Adelaide Hills I used higher
revs more often than I did fluffing around
in the city.