How to Retrofit Your Car with an Eco Engine

Your car may not be electric, but that doesn’t mean it can’t be cleaner.

More drivers want to reduce their environmental impact. They look for ways to do this without giving up their good vehicles. Climate change and fuel costs are important issues today. Eco engine conversion is a smart and sustainable way to make your petrol or diesel car greener and more efficient.

You can upgrade your car with modern tech. You don’t need to buy a brand-new EV or hybrid kit to complete electric retrofits. And the best part? It can save fuel, lower emissions, and extend your car’s usable life.

In this guide, we’ll cover what you need to know about retrofitting your car with an eco engine. We’ll look at types of conversions, costs, benefits, real-life case studies, and key tips to help you begin.

What is an Eco Engine Conversion?

An eco engine conversion upgrades your car’s internal combustion engine (ICE) to boost efficiency. You can also replace it with an electric or hybrid engine.

Common Retrofit Options:

• Mild Hybrid Conversions – Add an electric assist motor alongside the petrol engine
• Complete Hybrid Kits – Create a petrol-electric powertrain with regenerative braking
• Plug-in Hybrid Conversions – Similar to full hybrids but with external charging
• Battery Electric Vehicle (BEV) Conversions – Replace the engine with a fully electric drivetrain
• Biofuel or LPG Conversions – Reconfigure your engine to run on cleaner fuels

Each option has its pros, costs, and technical requirements — and we’ll walk you through them.

Types of Eco Engine Conversions Explained

1. Mild Hybrid Conversion Kits

How it works: A small electric motor assists the engine during acceleration and low-speed driving. This cuts down on stress for the fuel system.

Pros:

• Affordable (starting around £1,000–£1,500)
• Quick to install (2–4 days)
• Immediate fuel savings (5–15%)

Cons:

• Limited electric-only driving
• Best suited to city driving conditions

Example: Vitesco Technologies’ 48V Retrofit Kit

2. Full Hybrid Car Kits

How it works: It uses a petrol engine, a bigger electric motor, and a battery. Regenerative braking helps recover energy.

Pros:

• Fuel savings up to 30%
• Less brake wear
• Lower CO₂ emissions

Cons:

• Heavier system
• More complex installation

Ideal for daily commuters and professional drivers.

3. Plug-in Hybrid (PHEV) Conversions

How it works: A larger battery pack that can be externally charged allows 20–60 km of electric-only driving.

Pros:

• Excellent efficiency for city driving
• Access to low-emission zones
• Charge using off-peak electricity

Cons:

• Adds weight
• Costs between £4,000–£8,000 to install

4. Full Electric Engine Swap (BEV Conversion)

How it works: First, take out the engine and transmission. Then, install an electric motor, an inverter, and a battery.

Pros:

• Zero tailpipe emissions
• Minimal maintenance
• Instant torque and quiet operation

Cons:

• Expensive (typically £10,000+)
• Requires DVLA documentation updates
• May affect resale value

Ideal for classic car enthusiasts and EV DIYers.

See also: Best Eco Mods to Improve Fuel Efficiency in 2025

5. LPG or Biofuel Engine Conversions

How it works: Petrol engines get modified to use liquefied petroleum gas (LPG) or bioethanol blends.

Pros:

• Cheaper running costs
• Reduced NOx emissions
• Strong historical reliability

Cons:

• Fewer fuelling stations outside urban areas
• Limited incentives or grants

How Much Does It Cost to Retrofit a Car with an Eco Engine?

Conversion Type	Estimated Cost (GBP)	Timeframe	Fuel Savings
Mild Hybrid Kit	£1,000–£1,500	2–4 days	5–15%
Full Hybrid Kit	£2,500–£5,000	1–2 weeks	20–30%
Plug-in Hybrid	£4,000–£8,000	2–3 weeks	25–35%
Full Electric Swap	£10,000–£20,000+	3–6 weeks	100%
LPG/Biofuel Conversion	£800–£2,500	2–5 days	10–20%

Note: Costs vary by vehicle model, condition, and the provider’s labour rates.

What Kind of Cars Can Be Converted?

Best Candidates:

• Vehicles with enough space in the engine bay
• Cars in good chassis condition
• Lightweight vehicles
• Classic or collector cars with emotional value

Avoid Converting:

• Rust-damaged or heavily worn-out vehicles
• Cars with complex electronics
• High-end performance models are still under warranty

Benefits of Eco Engine Conversion

1. Environmental

• Lower emissions
• Better air quality
• Reduced noise, particularly in electric conversions

2. Financial

• Long-term fuel savings
• Exemptions from congestion/ULEZ charges
• Potential resale value boost in eco-conscious markets

3. Sustainability

• Prolongs the life of existing vehicles
• Avoids the emissions and resources involved in building new cars

Real-World Case Studies

Leila, 35 – Hybrid Conversion for a Toyota Yaris. “I didn’t want to scrap a car that still worked perfectly. The hybrid kit made it greener; I now average 70 mpg instead of 48. The extra range per tank is amazing.”

Jake, 51—Electric Conversion of a Classic Mini “I loved my Mini but hated the fuel smell. Now it’s electric and silent, and people always stop to ask about it. It was the best decision I made.”

Pitfalls to Avoid in Eco Engine Conversion

• Skipping certification: Ensure your installer complies with DVLA and MOT regulations.
• Underestimating battery size: Underpowered systems won’t last, especially for electric conversions.
• DIY errors: Improper cooling, wiring or battery handling can be hazardous.
• Neglecting paperwork: Always update your V5C logbook and notify your insurer.
• Assuming all insurers accept conversions: Some won’t use specialist eco or modified car insurers.

See also: Solar-Powered Car Accessories You Need

Step-by-Step Guide: How to Start Your Eco Engine Retrofit

Step 1: Choose Your Path

Choose from hybrid, plug-in hybrid, electric, or LPG conversion. Your decision should reflect your budget and goals.

Step 2: Find a Certified Installer

Trusted names in the UK include:

• Electric Cars (Wales)
• Lunaz (high-end restoration and conversion)
• EV West (kit suppliers and support for DIYers)

Step 3: Set a Realistic Budget

Include parts, labour, inspections, and a contingency fund (10–15%).

Step 4: Handle the Legal Bits

Ensure DVLA compliance, emissions certification, and proper insurance.

Step 5: Track Your Gains

Use a fuel tracking app or emissions calculator to monitor how much you save.

Conclusion: The Future of Driving Might Be in Your Garage

You don’t need to buy a brand-new Tesla to drive greener. With some planning and the right tech, you can turn your car into a part of the clean mobility revolution. Qualified specialists can help, too.

Retrofitting your car can be a great choice. Choosing a mild hybrid or going full electric makes life more sustainable. Plus, it can give new life to the car you love, making it cleaner and better for the environment.

Ready to Start Your Conversion Journey?

• Choose the conversion path that fits your lifestyle
• Connect with certified professionals
• Join the growing community of retrofitters driving change