Does Using LPG in Turbocharged Engines Cause a Loss of Performance?

Almost every driver considering LPG conversion carries the same worry: will my car get slower?

There is a historical justification for that worry. But the answer changes when we talk about today's systems — and in turbocharged engines there is even a detail that works in LPG's favour.

The subject has to be treated from three separate angles, because "performance" is not one single thing.

Octane Rating: LPG Has the Advantage Here

Octane shows how resistant a fuel is to uncontrolled combustion (knock). A high octane rating means the engine can run more aggressively.

The octane value of LPG used as autogas is above that of standard petrol on the market. This is particularly significant for turbocharged engines.

In a turbocharged engine the intake air is compressed and forced into the cylinder. As pressure and temperature rise, so does the risk of knock. The engine control unit retards the ignition advance to manage that risk — that is, it gives up some performance in order to prevent knock.

A fuel more resistant to knock reduces that pressure. LPG's high octane value is the strong side of the fuel in turbocharged engines, not the weak one.

Energy Density: It Affects Range, Not Power

On the other hand the energy LPG contains per litre is lower than petrol's.

The practical result is this: you consume more LPG by volume to cover the same distance. So even though the price per litre of LPG is around half that of petrol, the saving per kilometre is not directly half.

But note: this is a matter of consumption, not of power. The engine takes the energy it needs; it simply uses a greater volume of fuel to obtain that energy. When the system is calibrated correctly the amount of energy reaching the engine is the same as in petrol mode.

The difference in energy density affects the range of a tankful, not the response of the accelerator.

Air Displacement: Little Effect in Turbocharged Engines

In conventional LPG systems the gas is delivered into the intake manifold in gaseous form. Gas takes up volume, and that volume slightly reduces the amount of air that can enter the cylinder at the same time.

This is called a loss of volumetric efficiency and is the main reason for the power difference historically experienced in naturally aspirated engines. The technical root of the perception that "the car won't pull on LPG" in older generation conversions is largely this.

In turbocharged engines this effect is more limited, because the air entering the cylinder is already packed in under pressure by the turbocharger.

In direct injection systems the picture changes once more: because part of the fuel demand in these vehicles is already met through petrol, the effect of the gas displacing air is reduced further still.

So What Does the Driver Feel?

In a correctly installed system the combination of the three factors above appears as follows:

No difference is felt in accelerator response. Because the system adjusts gas injection timing to the engine's immediate needs, pedal response stays similar to petrol mode.

Revs build with the same character. When the turbo comes in, the expected acceleration does not change.

There is no jolt in gear changes. In vehicles with automatic transmissions the shift points are determined by engine load; as long as the system reports that load correctly the behaviour does not change.

The switch from petrol to LPG is not noticed. The transition happens automatically once the engine reaches a certain temperature and no noticeable fluctuation in revs is expected.

If There Is a Loss, What Causes It?

The great majority of performance complaints we meet in the field stem not from the fuel but from one of three things.

The wrong product choice. If a system produced for MPI has been fitted to a direct injection vehicle, problems are inevitable. This is not a situation that can be corrected by calibration.

Incomplete calibration. After installation the system has to be set according to the character of the vehicle's engine. A system left on a standard setting keeps the mixture either lean or rich; both spoil the driving feel.

Neglected maintenance. A blocked gas filter or a vaporiser that has reached the end of its life prevents the system from delivering the right amount of gas. This is a situation that appears over time and is easily corrected.

What all three have in common is this: the problem is not in LPG itself but in the application.

How Does 2A Prime Approach This?

2A Prime systems manage the mixture according to the engine's instantaneous load, rev and temperature data rather than a fixed table. The aim is for the system to change when the driving conditions change.

This is particularly important in turbocharged engines, because their load profile moves across a wide range. The needs of a turbocharged engine cruising at low revs in the city and of the same engine working under load on the motorway are different from one another.

In 2A Prime DI this management takes place integrated into the vehicle's own control architecture through IAS3 adaptation technology.

What About Naturally Aspirated Engines?

In naturally aspirated engines the loss of volumetric efficiency can be felt slightly more clearly, because there is no turbocharger pressurising the air entering the cylinder. The volume taken up by the gas comes directly off the amount of air.

Even so, in current systems this difference is not comparable with older generation conversions. Precise management of gas injection timing compensates for most of the loss. The driver is not expected to notice it in normal driving; a small difference may be felt at full throttle, uphill and under load.

In turbocharged engines this situation largely disappears anyway.

In Summary

With the right system and the right calibration, using LPG in turbocharged engines does not create a loss of performance that the driver would notice.

LPG's high octane value is an advantage for turbocharged engines. Its lower energy density affects range, not power. The loss of volumetric efficiency is considerably reduced in turbocharged and direct injection structures.

Performance complaints almost always stem from the choice of product, from calibration or from maintenance — not from the fuel itself.

Frequently Asked Questions

If LPG's octane is high, will my engine run more powerfully?

A high octane rating reduces the risk of knock and lowers the engine control unit's need to retard the ignition advance. This is an advantage, but conversion is not a performance upgrade. What should be expected is not a gain in power but the absence of a loss.

If consumption rises on LPG, where is the saving?

You consume more in litres, but the price per litre of LPG is noticeably below petrol. What is decisive is not the number of litres but the cost per kilometre, and that cost stays below petrol.

Do the engine oil and service intervals change after conversion?

The vehicle's own service schedule remains valid. In addition, the LPG system's own maintenance items come into play; filter replacement and periodic checks are the first among them. You can obtain the schedule specific to your vehicle from your authorised service.

Does towing capacity drop, can I tow a trailer?

In a correctly calibrated system there is no noticeable change in towing character. Because driving under load is one of the conditions that puts the system under most strain, having the calibration done specifically for the vehicle is especially important in this type of use.

How do I test performance after the system is fitted?

After installation the authorised service carries out a test drive and completes the calibration according to it. If you notice any behaviour in the first few hundred kilometres, fine tuning can be done at the service; this is part of the normal process and does not mean there is an additional problem.

Does fuel quality affect performance?

Yes. The mixture ratio and the content of the fuel can vary from station to station. Buying fuel regularly from points you trust makes a difference both to performance and to the life of the system.

Does LPG performance change with the air conditioning on?

The air conditioning compressor puts an additional load on the engine and that load is felt in both fuel modes. In a correctly calibrated system LPG mode does not create an additional disadvantage in this situation.

To determine the system suitable for your vehicle and to find your nearest authorised point you can reach us through our contact page.

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