VW 181 Facts & Figures

Date: Fri, 13 Dec 1996 10:39:06 +0100
From: Hanno Spoelstra <H.L.Spoelstra@wbmt.tudelft.nl>
Subject: LPG


As I run my '71 Bug on LPG, I have been getting requests from
several VW-enthusiasts about how to convert their own air-
cooled VW to run on LPG.

I live in the Netherlands (popularly known as Holland),
Europe. Since the rise of petrol prices due to oil crises in
the 1970s there has been an interest in alternative sources of
power for vehicles. LPG or propane has been accepted as a
environmentally friendly, high-octane automotive fuel in many
European countries, with the Netherlands and Italy on the
forefront. Here in the Netherlands LPG can be had at almost
every petrol station which is not located right next to
housing areas. There's are only low tax on LPG itself, but
road tax (depending on the weight of the vehicle) is between
two and three times as high.
A number of companies make LPG fuel systems, the state of the
art being electronically controlled, direct-injection systems.
These systems comply easily to the strictest exhaust
Many shops can fit LPG fuel systems off the shelf within one
day and many of them have been licensed to certify the systems
themselves. Since last year 25+ year old vehicles are road tax
exempt, so many people now buy an old American "gas guzzler",
Volvo Amazon, VW etc. and fit it with an LPG fuel system. This
lowers the petrol bill dramatically! As for a price
comparison: petrol costs US$4 to US$4.5 per US gallon, and LPG
cost US$1.3 per US gallon. (Fuel prices are comparable around
Europe: I really think US inhabitants should not complain
about their petrol prices...)

What does one need to run an air-cooled VW on LPG?
- A TANK: a pressure vessel is needed to store the LPG in a
liquid state. The tank in my Bug is fitted in the trunk up
against the rear of the dash. With an 80% filling limit it
holds up to 6 gallons only, but that is not problem as LPG can
be had everywhere. The petrol tank is retained, but another
option is to do away with the petrol tank so that a large LPG
tank can fitted in its place. The tank is fitted with an
electro-magnetic solenoid valve so that when the ignition is
switched off, the valve is shut. A copper pipe protected by
plastic transports the LPG from the tank to the pressure
regulator which is located near the engine.
- A PRESSURE REGULATOR: as LPG has to be stored under high
pressure to keep it in a liquid state, a pressure regulator is
needed to lower the pressure so that it can be fed into the
carburettor. When the pressure drops, the LPG expands from the
liquid state into the gas state. To be able to expand into gas
it needs a lot of energy. If this energy (in the form of heat)
would not be supplied from an outside source, the carburettor
would ice over instantly. The pressure regulator is therefore
fitted with a chamber through which engine coolant can flow to
supply excess engine heat to the LPG. Of course the air-cooled
VW engine doesn't have this source of heat, so the LPG is fed
through a double walled pipe which is welded into the exhaust.
Thus the LPG coming from the tank can subtract heat from the
exhaust gasses, expands, and is then fed into the pressure
regulator and on to the carburettor. It works fine provided
you check the pipe and exhaust regularly for leaks.
I know such a construction raises eyebrows with some federal
automotive certification authorities, but this problem can be
solved quite simply: instead of routing the LPG through the
double walled pipe, water is used as a heat-transfer medium. A
small water tank has to be fitted somewhere for that purpose
(under the fender in semi-auto fashion?). The pressure
regulator is fitted with in- and outlets for water, as in
water-cooled cars the regulator is spliced into the cooling
The carburettor is stock so that the car can also be run on
petrol. A venturi-type gas inlet piece is fitted either
between the air cleaner and carburettor or between the
carburettor and the inlet manifold.
Electro-magnetic valves are fitted between the LPG tank and
the pressure regulator and between the petrol pump and the
carburettor. This is to shut off either source of fuel when
the other is used. These two valves are fitted to the
bulkhead, the pressure regulator sits left of the engine
snugly fitted to the left inner fender.
- ENGINE MODIFICATIONS: no modifications are necessary,
provided your engine has hardened valves and valve seats.
Vehicles built to run on unleaded petrol normally have these.
The non-US spec. '71 Bug does not have hardened valves and
seats so I had to replace them.
The ignition has to be reset slightly: I run mine on 10 degree

I truly enjoy driving my '71 Bug (1300 cc 44 hp engine) on
LPG. Not only that it is a lot cheaper, but I do not pump lead
into the environment any more and the engine suffers a lot
less too. You can tell from the engine oil (it hardly gets
black any more) that there are a lot less aggressive by-
products which normally lead to a shorter engine life. Fuel
consumption is up a little - because LPG has less energy per
unit of weight - and typical water-cooled car fuel consumption
should raise some 20%. The Bug does not have to burn extra
fuel to heat up the water in its cooling system, so it uses
only some 10% more. I manage around 22+ mpg without having to
constrain my right foot.
Top speed should be a little lower, but not noticeable. Mind
you, we are allowed to drive between 60 and 75 mph on our
highways. Last summer I drove to southern France where on some
stretches of highway I managed 85 mph for prolonged periods.
Although propane gas burns at lower temperatures than a
petrol-air mixture, the cooling effect of this mixture on the
valves is absent. This results in higher cylinder head
temperatures, and some LPG-powered VW owners would not dare to
run it without an additional oil-cooler. Others just (like me)
enlarge the valve clearance by 0.002 in.
The past year I drove my Bug on LPG for over 15,000 miles
without any problems (I know of one which did over 250,000!).
Every now and then I run it on petrol to check if the pump,
fuel lines etc. are still in working order.

Basically it is a simple system, but I cannot tell you what
sort of system can be certified in the U.S. You will have to
find out for yourself and do a little experimenting. I do not
know about the prices and availability of LPG, but prices of
petrol in the U.S. are one of the lowest worldwide. But, LPG
is an environmentally friendly, high-octane fuel which could
be reason enough for some to start "experimenting" with LPG.

I hope this helps those of you who want to do this a little
further. A good source for further info on LPG in general and
automotive LPG conversion in the U.S. is given by Tom Jennings
on his home-page at http://www.wps.com/LPG/index.html.
If really needed (VW drivers do let each other down!) I am
willing to help the serious to get parts. But I think it is
possible and cheaper to get all the parts needed in the U.S.
or have them fabricated.

Good luck!

Hanno Spoelstra
Bloemendaal, The Netherlands, August 1996 (version 1.3)

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