LPG vs Gasoline Calculator - Conversion Kit Payback and Savings

Same engine, two fuel bills - what LPG conversion actually saves

An LPG conversion kit costs $800-2,500 upfront. It adds 10-20% to fuel consumption because autogas has lower energy density per liter. But LPG costs 40-60% less per liter than gasoline. The math usually works out - if you drive enough kilometers. This calculator runs the full comparison: gasoline cost vs LPG cost per 100 km, annual savings, conversion payback distance and a 5-year net profit projection.

How to use this calculator - step by step

Gasoline consumption - your car's average consumption on gasoline in L/100 km. Check the trip computer long-term average. Typical values: 5-7 L (compact), 7-10 L (sedan/SUV), 10-15 L (V6/V8).
Gasoline price - current price per liter at your local station. US average around $0.90/L, EU average $1.50-2.00/L.
LPG price - current autogas price per liter. Typically 40-60% of gasoline price.
Annual mileage - total kilometers driven per year. More mileage means faster payback.
LPG conversion cost - total installation price. Gen IV (MPI): $800-1,500. Gen V (TSI/GDI): $1,500-2,500.
Consumption overhead - how much more LPG the engine burns compared to gasoline. Default 15% works for most cars.
Read results - Before/After fuel cost comparison, payback period in months and kilometers, 5-year net savings.

Before and after: gasoline vs LPG cost breakdown

BEFORE - Gasoline only

8 L/100 km at $1.60/L

$12.80 /100 km

$2,560/year at 20,000 km

AFTER - LPG conversion

9.2 L/100 km at $0.75/L

$6.90 /100 km

$1,380/year at 20,000 km

Annual savings: $1,180. With a $1,500 conversion kit, payback comes at 25,424 km - roughly 15 months at 20,000 km/year. After 5 years, net profit reaches $4,400.

Conversion payback by annual mileage

Based on gasoline at $1.60/L, LPG at $0.75/L, consumption 8 L/100 km (+15% on LPG), conversion cost $1,500:

Annual km	Payback	Savings/year	5-year profit
5,000 km	61 months	$295	-$25
10,000 km	31 months	$590	+$1,450
15,000 km	20 months	$885	+$2,925
20,000 km	15 months	$1,180	+$4,400
30,000 km	10 months	$1,770	+$7,350
40,000 km	8 months	$2,360	+$10,300

LPG conversion types and their impact

System type	Cost range	Consumption overhead	Best for
Gen IV Sequential (MPI)	$800-$1,500	10-15%	Port-injected (MPI) engines, older cars
Gen V Sequential (GDI/TSI)	$1,500-$2,500	15-20%	Direct injection (GDI/TSI/TFSI) engines
Premium (Vialle/Prins)	$2,000-$3,500	8-12%	High-performance, luxury cars, lowest overhead

Practical examples

City commuter (10,000 km/year): 7 L/100 km gasoline, $1.60/L gas, $0.75/L LPG, $1,200 conversion.
Payback: 24 months. Annual savings: $590. 5-year profit: +$1,750.

Highway commuter (25,000 km/year): 8.5 L/100 km, $1.60/L gas, $0.75/L LPG, $1,500 conversion.
Payback: 12 months. Annual savings: $1,500. 5-year profit: +$6,000.

Sales rep (40,000 km/year): 9 L/100 km, $1.60/L gas, $0.75/L LPG, $2,000 Gen V conversion.
Payback: 8 months. Annual savings: $2,830. 5-year profit: +$12,150.

Low mileage driver (5,000 km/year): 6 L/100 km, $1.60/L gas, $0.75/L LPG, $1,200 conversion.
Payback: 56 months. Annual savings: $255. 5-year profit: +$75. Barely worth it.

V8 SUV (20,000 km/year): 14 L/100 km, $1.60/L gas, $0.75/L LPG, $2,500 conversion.
Payback: 11 months. Annual savings: $2,660. 5-year profit: +$10,800.

FAQ - Frequently asked questions

How much more fuel does a car use on LPG?

Most cars burn 10-20% more LPG per 100 km compared to gasoline. This is because LPG has about 25% lower energy content per liter. MPI engines with Gen IV systems typically add 10-15%, while turbocharged GDI engines with Gen V systems add 15-20%. Premium systems (Vialle, Prins) can keep it under 12%.

Is LPG conversion worth it for low-mileage drivers?

Below 10,000 km/year, payback stretches to 2.5-5 years. At 5,000 km/year, you might break even only after 4-5 years - by which point the system may need servicing. The sweet spot is 15,000+ km/year where payback drops below 18 months.

Does LPG damage the engine?

Modern sequential LPG systems (Gen IV and V) are safe for engines when properly installed and maintained. The main concern is valve seat recession in older engines without hardened valve seats - modern systems inject a lubricant to prevent this. Regular valve clearance checks every 30,000-50,000 km are recommended.

What maintenance does an LPG system need?

Annual service: $100-200. Includes filter replacement, leak test, injector calibration and software check. The LPG filter should be replaced every 10,000-15,000 km. The reducer (vaporizer) membrane typically lasts 80,000-120,000 km before needing replacement ($50-150).

Can turbocharged engines run on LPG?

Yes. Gen V systems are designed specifically for direct-injection turbo engines (TSI, TFSI, GDI). They inject LPG directly into the intake manifold with precise timing. Cost is higher ($1,500-2,500) but the system handles boost pressure and knock prevention. Some premium brands (Prins DLM, Vialle LPdi) even support liquid-phase injection for GDI engines.

Does LPG conversion affect resale value?

Mixed impact. In markets where LPG is popular (Poland, Italy, Turkey, Netherlands), a quality LPG system adds value - buyers see it as a fuel-saving feature. In markets where LPG is rare (US, UK), it can reduce value by $500-1,000 as buyers worry about unfamiliar technology. A professionally installed system with documentation from a reputable brand holds value best.

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