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LPG conversion of a naturally aspirated engine: suitable engines, costs and used-car checks

Which naturally aspirated engines take LPG well, what a conversion and the tank involve, and what to check on a used car running on gas.

October 23, 2026

LPG conversion of a naturally aspirated engine: suitable engines, costs and used-car checks

Key takeaways

The easiest engine to convert is a naturally aspirated petrol engine with indirect injection (MPI), such as the 1.4 MPI in the Hyundai i30 or Kia Ceed. A direct-injection engine, such as the 2.0 Skyactiv-G in the Mazda 3, needs a more complex and more expensive system.
A basic sequential conversion of a four-cylinder engine with indirect injection is the cheapest option. For direct-injection engines, prices start considerably higher. Prices vary by country and workshop.
On a used car with LPG, the most important things besides the engine's condition are the state of the valves and valve seats, a documented system and the age of the tank. A tank nearing the end of its service life means an extra cost.
On short trips, LPG saves less. The system starts on petrol and switches to gas only once the engine has warmed up.

A naturally aspirated engine on LPG combines a simple non-turbocharged petrol engine with a cheaper fuel. LPG is liquefied petroleum gas, usually a mixture of propane and butane. The car burns it through a separate fuel system, while the petrol system remains in place. The "no turbo" label, however, says little about suitability for gas. What matters more is how the engine injects petrol, how durable its valves are, and who installed and serviced the system.

When is a naturally aspirated engine on LPG a good idea?

A naturally aspirated engine draws in air without a turbocharger or a mechanical supercharger. For LPG, what matters more is where the engine meters its petrol.

With indirect injection, petrol goes into the intake manifold. A sequential gas system adds its own LPG injectors there, so installation is straightforward. With direct injection, petrol goes straight into the cylinders. The gas system then has to deal with cooling the petrol injectors and usually also uses some petrol when running on gas.

Engine type	What it means for LPG
Naturally aspirated engine with indirect injection (MPI)	The simplest and cheapest conversion. The durability of the valve seats and the quality of the kit are decisive.
Naturally aspirated engine with direct injection	A more expensive system designed for the specific engine; some petrol is usually also used when running on LPG.
Naturally aspirated engine in a full hybrid	The system has to cope with the engine being switched off and restarted frequently. The saving is smaller, because the hybrid already uses little petrol.

The MPI designation therefore helps narrow the choice. Whether a specific engine can take gas and whether it needs valve protection can only be determined by a specialist workshop based on the engine code.

What kind of driving does LPG make sense for?

LPG pays off mainly for those who regularly drive longer distances, on which the engine runs on gas for most of the journey. On short town trips, the car covers a large part of the distance on petrol, because the system only switches to LPG once the engine has warmed up. The Prins VSI system, for example, always starts on petrol.

With low annual mileage, a well-kept petrol used car usually makes more sense than a cheaper example with LPG and neglected maintenance.

Which used cars with a naturally aspirated engine to shortlist?

The Hyundai i30 and Kia Ceed are among the easiest candidates thanks to indirect injection. The Mazda 3 and Toyota Corolla show why not all naturally aspirated engines can be judged the same way. The Škoda Fabia is a size smaller, but its simple MPI engine makes it worth a look.

Model and generation	Engine	Injection	What matters for LPG
Hyundai i30 III (from 2017)	1.4 MPI 73 kW (2017 model-year line-up)	indirect, multi-point	A typical conversion candidate. It is worth finding out whether the workshop recommends valve protection.
Kia Ceed III (from 2018)	1.4 MPI 74 kW (100 PS), offered from launch in 2018	indirect, multi-point	Technically close to the i30. An example with a known history takes priority.
Škoda Fabia III (2014–2021)	1.0 MPI 44 and 55 kW	indirect	A three-cylinder with only 95 Nm of torque. The cost comparison below refers to four-cylinder conversions.
Mazda 3 IV (from 2019)	2.0 Skyactiv-G 122, 90 kW	direct	Conversion requires a system for direct injection and is more expensive.
Toyota Corolla XII (from 2019)	1.8 Hybrid, system output 90 kW (122 PS)	indirect	The gas system has to work with the hybrid powertrain. The saving is smaller because of the low petrol consumption.

For a car that has already been converted, the most valuable thing is a documented combination of engine, system type and service history. The phrase "it runs on gas without any problems" is no substitute for paperwork.

How much does an LPG conversion cost and what else to budget for?

A sequential conversion of a four-cylinder engine with indirect injection is the cheapest type of conversion. The price is lowest with a basic kit and a cylindrical tank. A more expensive system, a toroidal tank and optional extras push the price up. Converting direct-injection engines is considerably more expensive. Prices vary from country to country and between workshops, so ask several specialist installers for a quote for your specific engine.

What a conversion budget includes

When comparing quotes, check which of these items are included in the price:

Item	What to check
Gas system and installation	The system brand and type, and whether it is designed for your engine code
Tank	Cylindrical or toroidal, and its capacity
Inspection or certification of the installation	Whether it is included or charged separately
Recording the conversion in the vehicle documents	Who handles it and what the local authority charges
Optional extras	For example, a valve protection system

The conversion must be approved and recorded in the vehicle's registration documents. The procedure, the documents required and the fees vary by country, so check them with the local vehicle registration authority.

The conversion also adds running costs: servicing the gas system, replacing its filters and, on some engines, more frequent valve adjustment. Routine servicing of the petrol engine stays the same; spark plugs and ignition, on the other hand, are under more strain when running on LPG.

The tank can change the value of a used car

An LPG tank has a limited service life, and its manufacture date is shown on its plate. In some countries, the tank has to be replaced after a set period, so check the rules that apply where the car will be registered. A toroidal tank is ring-shaped and usually sits in place of the spare wheel. On a used car with an older conversion, a new tank can therefore eat into part of the price advantage.

How long does it take for LPG to pay for itself?

The payback period depends on the difference between petrol and LPG prices, on annual mileage and on what share of the distance the car covers on gas. A car uses more litres of LPG than of petrol, and some systems also use petrol when running on gas. The saving therefore cannot be calculated simply as the difference in pump prices multiplied by petrol consumption.

How the car is used	What to expect from the economics of LPG
Regular longer commutes	Most of the distance on gas, the conversion pays for itself fastest.
Mostly short cold trips	A high share of petrol, the payback period drags on.
Low mileage and replacing the car soon	The investment in the conversion may not pay off.
Buying a used car that has already been converted	You do not pay for installation, but you take on the servicing and wear of the system.

A healthy engine always comes first. A cylinder head repair will swallow the savings from years of driving on gas.

What to watch for on a used car with LPG?

Valves and valve seats

LPG burns at a higher temperature and lacks the lubricating effect of petrol. On less robust engines, the valves and their seats therefore wear faster when running on gas. This shows as a loss of sealing, rough running and, in the worst case, a burnt valve. On engines that require valve clearance adjustment, records of the adjustment are very valuable.

Wear is reduced by systems that meter a protective fluid into the intake, such as Prins ValveCare. They cannot, however, help an unsuitable engine or a badly set mixture.

Poor tuning and neglected ignition

Jerking when switching over, misfiring under acceleration or an illuminated engine warning light are not normal characteristics of LPG. The cause may be the gas system, worn spark plugs and coils, or a fault in the engine itself.

The car must run perfectly on both fuels. If the seller refuses a drive on petrol or dismisses a fault with "it only does that on gas", they are selling an unsolved problem.

Missing documentation

Without paperwork for the system, you do not know what system is in the car, who serviced it or when the tank's service life ends. Further servicing is then more expensive and uncertain. A missing certificate of approval for the conversion also complicates recording it in the vehicle documents.

Pre-purchase checklist

Documents: LPG recorded in the registration document, the system type and proof of the conversion.
Tank: the manufacture date on the plate, and whether it is approaching the end of the service life permitted where the car will be registered.
Servicing: records of LPG maintenance and, on sensitive engines, of valve adjustment.
Test drive: a cold start on petrol, a smooth switchover to LPG and acceleration on both fuels.
Diagnostics: stored faults, how the engine runs and, if leaking valves are suspected, a compression test.
Installation: a smell of gas, damaged lines or loose parts are reasons to walk away from the purchase.

For cars offered by Carvago, some of these points are covered by the CarAudit™ inspection: a technician carries out diagnostics, a technical inspection and a test drive before the car is sold.

Carvago: the right engine in a car in good condition

Searching for a Hyundai i30 or Kia Ceed with the 1.4 MPI only in your local area often means taking whatever is available. Carvago offers roughly a million cars from dealers in several European countries, so the choice in practically every segment is larger, usually by an order of magnitude, than on the local market. You can find the specific engine in an example with a good history and do not have to accept a neglected car just because it has the right engine.

Before sale, every car is inspected by a technician as part of CarAudit™ at up to 270 checkpoints. The inspection includes the car's history and legal status, a technical inspection, diagnostics and a test drive. The customer knows the result before deciding to buy the car, and Carvago guarantees the condition stated in the certificate. Any LPG conversion is then a matter for a specialist workshop, based on the specific engine.

Before sale, Carvago buys the car from the original seller, becomes its owner and takes on its risks. The customer buys directly from Carvago. Carvago takes care of registering the car in the customer's country, including the paperwork, and delivers it right to the customer's door.

FAQ

Does LPG reduce the power of a naturally aspirated engine?

With a correctly chosen and tuned system, the difference in normal driving is small. A marked loss of power, jerking or misfiring indicate a fault or poor tuning.

Does an LPG tank take up the whole boot?

A toroidal tank usually takes the place of the spare wheel and the boot floor stays free. The spare wheel is then replaced by a repair kit. A cylindrical tank sits directly in the boot and takes up a noticeable part of it.

Is LPG the same as CNG?

No. CNG is compressed natural gas, mostly methane. It has different tanks, filler connectors and system, so a car converted to LPG cannot fill up with CNG.