You had LPG installed, drove for a few days, and noticed something. The engine sounds quieter, throttle response feels slightly softer, and the trip computer shows higher consumption than on petrol. The natural reaction is to wonder whether that is normal. In the vast majority of cases, it is. Petrol and auto gas are two different fuels with different combustion physics, and those differences have to be felt. What matters is recognising the line between normal physics and a real problem.
Two fuels, two sets of physics
LPG has a higher octane rating than most petrol, typically 105-110 octane compared to 95-98. This means LPG tolerates greater compression without knocking, which is actually good for engine health. However, LPG has a lower energy density per litre. One litre of LPG contains roughly 10-20% less energy than a litre of petrol.
The consequence is straightforward maths. The engine needs to inject more litres of LPG to extract the same amount of energy. If your car uses 8 litres of petrol per 100 km, expect around 9-10 litres on LPG. That is not a fault, not a bad calibration, and not a reason for concern. It is physics, and it applies to every LPG system on the planet.
LPG also enters the engine in a gaseous state, whereas petrol enters as a liquid that evaporates inside the cylinder. The combustion process differs accordingly. The flame front spreads at a different speed, cylinder pressures are slightly different, and all of this affects the character of the engine that you feel through the steering wheel and pedal.
What normal feels like behind the wheel
At our workshop, we always tell drivers what to expect in the first few days after installation. A normal difference on a properly calibrated system is mild and consistent.
The engine on LPG typically runs softer and quieter than on petrol. Many drivers describe it as "smoother." The exhaust note may sound marginally different. During calm city driving, the difference is barely perceptible.
At the top of the rev range, under full acceleration, you may notice a slightly weaker response. On some systems, that means 5-8% less power at wide-open throttle. In everyday driving this is negligible, but if you push the car to its limits on the motorway, you might feel it. Some modern systems have a function that automatically switches back to petrol at full throttle precisely to eliminate this gap.
An important moment is the switchover from petrol to LPG after starting the engine. Every LPG system starts on petrol, runs for 1-3 minutes while the engine and reducer warm up, and only then transitions to gas. On a healthy system, that transition takes a fraction of a second. You feel a brief, barely noticeable change in engine behaviour, and that is it. No jerking, no stalling, no drama.
Why temperature affects the switchover
The reducer, a key component of the LPG system, uses heat from the engine's coolant to vaporise LPG from liquid into gas. Until the engine reaches operating temperature, the reducer cannot work properly.
In summer, when ambient temperatures are high, the engine warms up quickly and the switchover happens after a minute or two. In winter, especially below freezing, warm-up takes longer. The engine may run on petrol for 4-5 minutes before the system switches. This is completely normal and is actually a protective function. The system waits until the reducer is warm enough to deliver a stable flow of gas.
If you notice your car taking longer to switch over in winter, do not treat it as a fault. Only if the system never switches to LPG, or switches and then immediately reverts to petrol, should you have the reducer and temperature sensor checked.
What is not a normal difference
A normal difference is mild, consistent, and predictable. A problem shows itself through distinctly different symptoms.
Jerking or hesitation that appears only on LPG but not on petrol is never normal. A significant drop in power where the car barely pulls on gas is also not physics but a fault. If you notice poor running specifically on LPG, the issue usually lies in calibration, injectors, or the reducer.
Backfiring through the intake, a smell of gas in the cabin, a check engine light that comes on only when running on LPG, or frequent unwanted switches back to petrol, each of these symptoms requires inspection. The LPG computer returns the car to petrol when it detects an irregularity. That is a safety function, but the cause of the irregularity needs to be found and fixed.
If you are unsure whether the difference you feel is normal or a fault, there is a straightforward test. Compare behaviour on petrol versus LPG, that article explains how to separate an engine problem from an LPG system problem.
System generation makes a difference
How much difference you feel between petrol and LPG also depends on the generation of the LPG system.
Older venturi systems (first and second generation) mixed gas with air at the intake manifold entrance. Calibration was coarse, the difference in engine behaviour was greater, and consumption was less predictable.
Modern sequential systems (fourth generation and newer) inject gas individually into each cylinder, synchronised with the petrol ECU. The difference in running on such a system is minimal. Many drivers say they forget which fuel they are on after a quality installation.
Systems adapted for direct-injection engines go a step further and require more precise calibration. The behavioural differences there are more specific, but on a correctly calibrated system, the driving experience is virtually identical. More about the differences between LPG system generations can be found in our system selection guide.
Calibration is the key, not luck
The difference between a system that feels "almost like petrol" and one that obviously runs differently comes down to calibration. It is not a matter of luck or equipment brand. It is a matter of how precisely the technician adjusted the injection maps for your specific engine.
At our workshop, we complete every installation with a thorough calibration on diagnostic equipment. We monitor lambda sensors, petrol ECU corrections, and response under different loads. The goal is for the petrol ECU to "not notice" that the engine is running on gas at all.
Calibration is not a one-time job. Over the course of normal use, injectors wear, the reducer changes slightly through ageing, and a periodic check-up every 10,000-15,000 km ensures the system stays within optimal range. If your LPG consumption starts creeping above the normal ratio compared to petrol, review the factors that affect LPG consumption before concluding that something is wrong.
If you feel that the difference between petrol and LPG on your car is not what it should be, come in for an inspection. We can provide precise diagnostics and recalibration at our LPG service centre, or contact us to book an appointment.