LPG Conversion

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If you do a high mileage in a thirsty classic, converting to LPG could save money as well as making your car more environmentally friendly

(Although this article was written for a European audience, the interest in alternative fuels is worldwide. Ed.)

The petrol engine has been developed to a high state of efficiency and it’s proving hard for manufacturers to come up with anything that comes close when total impact on the environment, including manufacture, is considered. Catalytic converters don’t help much, because the good they do in cleaning exhaust gases is balanced by the environmental destruction caused in extracting the platinum to make them.

There’s surely a future for existing engines to be kept running as efficiently as possible. One day someone will find the catalyst that simply splits water into its constituent hydrogen and oxygen, allowing it to be burnt cleanly in existing internal combustion engines. Until then, the best alternative is LPG, which is readily available and costs considerably less than petrol.

LPG is a hydrocarbon fuel but it’s plentifully available as it’s a by-product of oil and gas production. A blend of propane and butane, it’s non-toxic, has a high calorific value and extremely high combustion efficiency. It burns relatively cleanly, producing negligible sulphur or metal pollutants, and can be fitted to virtually any engine. Fleet users can even bunker their own fuel, reducing costs even further.

Of course, as with petrol, LPG is used more efficiently in a multi-point sequential computer-controlled fuel injection situation, but the fact that it emits 80% of the carbon dioxide of petrol and a tiny fraction of the nitrous oxide or fine particles of diesel mean that it is still significantly less polluting when used with older technology, including classic carburetors.

Because it is so clean-burning and free of additives, LPG naturally contains no valve seat protection, so if you have soft valve seats, the head will have to come off for hardened seats to be fitted – but that’s likely to be necessary anyway if you’re doing a significant mileage on unleaded petrol.

LPG is stored under pressure, at 10-12 bar (140-170psi) – and turns to liquid, occupying less space, when pressurized. Though LPG is now widely available, almost all conversions retain the original petrol system alongside LPG and can switch between them. This inevitably means space loss, usually in the boot, for the LPG tank – though clever solutions include under-floor mounting and ditching the spare wheel in favour of a doughnut-shaped tank. In fact, while fuel injection systems still need petrol for starting, with a carburetor car you could throw away the petrol system altogether.

LPG is far more widely used in continental Europe, reaching as high as 20% market penetration in Poland compared to 0.5% (140,000 vehicles) in the UK. You will need filler neck adaptors, though, before taking your LPG car to Europe, with different adaptors needed in different areas: see

Calor supplies all LPG under the Autogas brand name in the UK and a useful website – – lists all 1304 stations selling LPG and 209 installers, plus the cheapest place to buy LPG. However, not all these installers are approved by the LPGA, the industry governing body. While it’s not essential to be approved, insurers don’t like non-approved installation: there’s no additional premium from most insurance companies if an approved installer is used.

While a wide range of companies can supply and fit conversions to modern cars, especially larger-engined models, not all are interested in classics. The LGPA recommends Autogas 2000 and FES Autogas as having most experience with older cars.

‘We’ve done everything from the Queen’s Rolls-Royce Phantom to quad-cam Aston Martin V8s,’ says Autogas 2000’s Chris Wise. ‘The only thing you’ve got to be careful with is valves, and to keep an eye on the clearances with cast iron heads. Especially with larger engines, there’s no sense fitting hardened valve seats straight away – they usually run fine as they are. The octane of LPG is higher than petrol – usually a little over 100 octane – so the engine will run without pinking and you can advance the ignition to suit. Fuel vaporisation becomes a thing of the past and we have quite a lot of interest from motor sport now that they are compelled to use pump fuels.

‘Older fuel injection systems can be difficult to convert because they rely on fuel circulation for cooling; we’ve done Bosch K-Jetronic systems but a Lucas mechanical system would be very hard. Carburetors are no problem – you just need the correct mixer tap, though some of the conversion parts are harder to find now. Typical costs would be $1700+tax for a Rolls-Royce Silver Shadow on carbs with a 100-litre tank, dropping to $1500 for a 2-litre four-cylinder single-carb Ford Pinto, such as a Cortina.’

Dai Brace from FES Autogas has seen conversions fitted to an even wider range of classics: ‘We’ve done everything from Morris Minor to Scimitar, Mini to Bentley. I converted my Saab 96 V4 and it ran fine without hardened seats,’ he recalls. ‘We use an Australian product called Flashlube which drip-feeds additive into the manifold to give valve seat protection whether the car’s on gas or petrol. I also converted a friend’s Mini recently – we fitted a Metro unleaded head, as even the Flashlube would have struggled with a standard A-series engine. Now he can do over 250 miles for $16.00!

‘We also supply specialist conversions for air-cooled engines in VW Campers, Beetles and even 2CVs. They use a special exhaust heat exchanger to vaporise the gas, whereas normal systems use the cooling water. With the specialist parts, the VW conversion comes out at about $1300, but a simple system like the Mini one, provided the engine is already converted to run on unleaded, comes out at about $1000.

‘If the engine’s worn out and carboned-up, it’s best to rebuild it and run it in on petrol before changing to gas. Then it’ll last for ever: you save on oil changes, because the gas burns so much more cleanly and there’s no wash on start-up – a 6000 mile change can easily be extended to 10,000.’


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