discussed in this article include -
the USA there is a lot of possible variations in fuel additives
because lead has been replaced with MTBE, but this is not
true everywhere. Some history -
lead (TEL), colorless, poisonous, oily liquid, Pb(C2H5)4,
was added to gasoline for internal-combustion engines as an
antiknock agent. TEL needed ethylene dibromine and ethylene
dicloride scavengers mixed in to prevent an excess of lead-oxide
build up in the engines, and although the story revolved around
lead - it was as much for the scavengers that lead was removed.
BUT - along comes the MTBE (methyl tertiary butyl ether) alternative,
and the need for higher proportions of aromatics (benzene
etc). MTBE itself tends to increase the NOx levels
in the exhaust (although it reduces carbon monoxide and hydrocarbons).
It also requires an increase in fuel consumption (since 11%
MTBE results in 2% used oxygen in the fuel, and the increased
requirement for aromatics for their natural high octane numbers
means there is not THAT much decrease in the overall pollution
the final days of lead in the late 60s they were adding only
0.2 gm/litre (down from 1.05 gm/litre - the practical limit
was 1.1 gm/litre), and this reduced the halogen scavengers
too, so the last leaded fuels were not nearly as nasty as
they had been 20 years previously.
(lead replacement petrol), which contains MMT (methylcyclopentadienyl
manganese tricarbonyl) has proven to be a poor substitute
in Australia -- it causes spark plug fouling with resultant
hard starting and rough running. It is not popular, and lots
of folks with older cars which needed lead are using unleaded
with additives instead (some of which contain MMT so go figure!)
to the lengthy FAQ on fuel I have, there is some variation
in the US brands due to the no-lead rules and the resulting
substitutes for higher octane fuels. (I don't know if different
'cheaper' brands or "name" brands would be better.)
FAQ I have indicates it's usually better to stay away from
additives, apart from a bit of upper cylinder lubrication.
Most of these are just kerosine-based anyway, so I wouldn't
bother. The VW engine doesn't need extra upper cylinder lubrication
because the valves don't have valve seals (they slope down
at the spring end so excess oil runs away from the cylinders),
and since they don't use valves seals they get plenty of lubrication
from the oil on the tappet end -- it works it's way up the
valve stems by capilliary action. The cylinders get plenty
of oil too, so it's not needed for the rings etc.
the United States lead additives have been completely banned,
and compounds such as Methyl Tertiary Butyl Ether (MTBE) are
added to raise octane rating and promote more-thorough combustion.
Methyl Tertiary Butyl Ether
MTBE (Methyl Tertiary Butyl Ether)
is an oxygenate that was introduced as a gasoline additive
in the US two decades ago to replace TEL while remaining harmless to catalytic converters. The US fuel laws allow up to 2%
total oxygen in the fuel -- that's 11% MTBE. This varies a
bit from State-to-State, and summer-to-winter. I don't think
all states actually use it, and there are definitely different
amounts in some areas where it IS used. Much of California
has up to 11% MTBE, and Denver too, but areas outside Denver
have a different fuel formulation (lower MTBE or no MTBE)--
some Denver folks fill up outside the city when they can because
the car runs better.
Since MTBE is oxygenated, an 11% concentration makes carburetted cars
run 2% lean. The slight hesitation that many VW owners experience is almost
certainly a lean burn condition for a number of reasons, one of which is MTBE.
VWs like a fractionally rich mix, which is part of what killed
them off in the US (higher emissions). It is very difficult
to sufficiently control the emissions from an aircooled engine,
and they don't like lean burn conditions.
Cars with engine-management computers
cope with MTBE by upping the fuel delivery for correct mixtures,
but older carburetted cars can't adjust themselves on the
Hopefully a slight choke adjustment will help this, or you may increase the size of the main jet (say from X125 to X127.5 -- more than enough to compensate for 11% MTBE in the fuel). So if your car is stuttering on acceleration and running a little hot when cruising, increasing the main jet by one size might be the fix that is needed.
Just a change of the brand of fuel might help, too. Some companies use more aromatics (which have natural high octane ratings) and less MTBE to
get the right octane number. The 60 page FAQ and California
EPA documents I have on it says there is enough variation
in fuels in the US to make it worth experimenting with brands.
They also say you should be prepared to change brands winter/summer
if you do find an improvement, because the formulas change
California is requiring reduced
aromatics because they also result in more pollutants, but
this is a double whammy. You then need more MTBE or Tertiary Amyl Ether (TAME) or
one of the other oxygenates to increase the octane number,
and then you burn more fuel in the computerised cars, which
increases total pollution anyway. Fascinating.
MTBE doesn't do anything for
the valve seats. With vintage and classic cars the loss of
lead is not a huge problem -- they do only small mileage,
and valves seat damage usually only occurs when the valves
are running really hot (engine working hard), so going for
a car club cruise in your 1930 MG once a month is not usually
But for many of our cars on the
road, being used every day, and still having cast iron heads,
it's a REAL problem. They really do need the lead coating
(or a substitute) on the exhaust valves to prevent damage.
MTBE doesn't help there -- it's
only an octane booster. In some countries Lead Replacement
Petrol (LRP) is available which has lead subsitutes to protect
the valve seats from valve seat recession, but fortunately
for VW owners the VW engine has hardened steel valve seats
in the aluminium heads so valve seat recession is not a problem.
The VW engine does NOT need lead or lead substitutes in fuel.
In fact if you have LRP in your country -- DON'T use it in
the VW engine. The VW engine runs hotter than it's water-cooled
cousins, and burning LRP in them tends to bake the LRP residues
onto the spark plugs, causing rough running and hard starting.
MTBE is falling out of favor
in the US -- it's being found everywhere in the environment,
with what effect I don't know, as a result of leakage from
service station sites and tanker spills, etc. It mixes readily
with water, so it easily contaminates ground water and so
on. And of course since it contains "used" oxygen there's
less "fuel" in the fuel, so fuel consumption INCREASES, which
increases the total exhaust emissions and so on. California
has moved to ban the addition of MTBE by 2002.
Until recently we hadn't gone
down the MTBE path in Australia, and I was in hopes that we
wouldn't. However now (March 2003) Woolworths (a large supermarket
chain in Australia which has an associated fuel outlet) began
selling a fuel called Woolworths Petrol Plus. Their web site
indicates that this petrol (imported into Australia, not refined
in here) contains up to 7% MTBE, and an average of between
2 and 3% MTBE -- but not in Western Australia or South Australia,
where oxygenates are banned.
2-3% MTBE causes no problems
for the VW engine, but 7% MTBE will run the engine about 1%
lean, which might be noticable in some cars (hesitation, running
hot). So if your Australian bug has a tank full of Petrol Plus
and the engine feels a little sick, try switching to one of
the other brands and see if that helps. If it does, then you'll
now know WHY it helps, as no other brand in Australia uses
MTBE laced petrol.
Folks in Australia are getting REALLY
I wonder what they will replace
MTBE with? With MTBE gone and the aromatics like methyl benzine
(toluene) being reduced too (both have a high octane number),
it's going to be hard to get the octane number high enough.
alcohol (ethanol) is added to fuel in many places to reduce
costs and to extend the life of our oil reserves. Ethanol
is soluble in gasoline, and in some countries it's common
enough to see 10% ethanol blends, and they have been cases
where up to 20% has been added. In Australia for example,
a common mix (available in some states only) is E10 (10% ethanol).
There has been lots of discussion about how the addition of
ethanol helps the combustion process and how it will help
the sugar-cane farmers in Queensland (they make it from otherwise
wasted molasses so it would be a boost to sales).
no one has picked up the subject of older carburetted cars.
The addition of ethanol to gasoline causes big problems in
a VW engine, as ethanol makes the engine run 4% leaner. To compensate for 10% ethanol in gasoline (called E10 in some places), you must increase the main jet by two steps (e.g., from X125 to X130) and the idle jet by one step (from 55 to 60), as 10% ethanol makes the engine run 4% leaner.
consideration -- production of pure anhydrous ethanol is difficult
and expensive, as it forms an azeotrope with water on distillation
-- about 96% ethanol. This 4% or so of water will require
an increase the jet sizes just a little to cope with the water
(main jet maybe 185, and idle maybe 80-82 for an ethanol-only
attracts water of course, so storage in a car's fuel tank
in the open weather means it will absorb condensation, and
you won't know it's happening until the engine starts to sputter.
VW enthusiasts wonder if they can run their 1500cc or 1600cc engines
on ethanol. They envision the ability to produce ethanol on
their own from substances that don't release hydrocarbons
when burned (such as corn and other biomass). It's all part
of a hope to have a bio-Bug, a totally enviro-friendly Bug.
would be easy enough to run a VW engine on ethanol. The main
thing is that using ethanol would require fuel jets approximately
200% bigger in cross section than gasoline needs, because
ethanol contains a lot of "used" oxygen which is no longer
available as fuel.
if you have a 34PICT/3 carburetor with size 55 idle and 127.5 main jets,
you'd need to increase those jet sizes to about 78 idle, and
the main jet to about 180.
For information, the sizes indicate
the hole size in mm, so 127.5 is a hole size of 1.275mm. So
a hole size of 1.8mm has about twice the cross section of
a hole size of 1.275mm - hope that makes sense.
I really don't
know what size you'd need the air correction jet though -
whether larger (for leaner at high speed) or smaller (for
richer at high speeds) I don't know. I'd GUESS smaller (for
richer, since you need MORE fuel with the ethanol), but that's
only a guess. So it if the air correction is normally about
an 80, you could try a 60 or something like that.
think the engine itself would cope okay, so long as you weren't
asking for bags more power - just what the standard cam etc
engine would tend to run much cooler than running on gasoline,
since it has a much higher latent heat of vapourisation (it
cools a lot as it evapourates). So a cylinder head temperature
guage might be useful (before the change too, to get an idea
of normal temperatures) so you could perhaps partly block
the fan intake (a circular piece of metal with a hole in the
middle would be the way to do it) to keep the operating temperatures
near normal - otherwise the wear rate on your cylinders and
pistons would accelerate.
is about 115 octane (using the US AKI measurement) so you
could increase the compression ratio to about 10:1 to make
use of it. That's a lower compression than burning ethanol
in a water-cooled car because the VW runs hotter and so must
use a lower compression for the same octane rating. For that
sort of compression you'd have to make sure your engine had
case savers, and it would be wise to use the 10mm head studs
with 14mm case savers, rather than the 8mm studs and 12mm
case savers. The larger case savers will give more protection
from studs pulling out with the higher combustion pressures
(if you increase the compression).
you did increase the compression, you should normally reduce
your amount of ignition advance a little, but the higher octane
number of ethanol would indicate more advance, so you may
have to play about with that one.
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