Making an electric car typically means converting an existing gasoline vehicle by replacing its engine and fuel system with an electric motor, battery pack, controller, and charger. A basic conversion kit for a compact car starts around $14,000, while higher-performance packages with Tesla drivetrains can run $24,000 to $68,000 before labor and the donor vehicle. It’s a serious engineering project, but one that hobbyists and small shops complete regularly.
The Four Core Components
Every electric vehicle, whether factory-built or converted in a garage, relies on the same basic hardware. The electric traction motor replaces the combustion engine and drives the wheels. A traction battery pack stores the electricity that feeds the motor. A power electronics controller sits between the two, managing how much current flows to the motor and therefore controlling your speed and torque. And an onboard charger converts AC power from a wall outlet or charging station into DC power the battery can absorb.
In a conversion, you’re removing the engine, exhaust system, fuel tank, and radiator, then installing these four components in their place. Most builders also retain the existing transmission, power steering pump (swapped to an electric unit), and braking system, though the brake booster usually needs to be replaced with an electric vacuum pump.
Choosing a Motor Type
The two main options for a conversion are brushless DC motors and AC induction motors. Brushless DC motors are more energy efficient because they use permanent magnets and don’t waste energy generating an electromagnetic field the way AC motors do. They also deliver flat, consistent torque across a wide speed range, which makes them feel responsive and predictable in a car. AC induction motors tend to lose torque as speed increases, but they’re rugged and widely available from salvaged production EVs.
For most conversion projects, a brushless DC motor in the 50 to 150 kilowatt range is the practical sweet spot. Smaller motors suit lightweight donor cars like old VW Beetles or Miatas, while heavier trucks or SUVs need more power. The NetGain Hyper 9 is one of the most popular conversion motors, available in integrated kits that bundle the motor, controller, and wiring harness together.
Battery Pack Options
The battery pack is the most expensive single component and the biggest factor in your car’s range. Two lithium-ion chemistries dominate the EV world: LFP (lithium iron phosphate) and NMC (nickel manganese cobalt). LFP cells are heavier for the same energy storage, but they’re more thermally stable, tolerate more charge cycles before degrading, and cost less per kilowatt-hour. NMC cells pack more energy into less weight, which translates to longer range, but they’re pricier and require more careful thermal management.
For a first conversion, LFP is the safer and more forgiving choice. A pack in the 20 to 40 kilowatt-hour range will give a compact car roughly 60 to 120 miles of range depending on driving habits and vehicle weight. The NetGain integrated kits, for example, offer packs from 21.2 kWh ($13,681 for the full system) up to 37.1 kWh ($17,274). Builders who want more range or performance often source used battery modules from wrecked Teslas, Chevy Bolts, or Nissan Leafs and assemble custom packs.
Battery Management System
Every multi-cell battery pack needs a battery management system, or BMS. This is the electronic brain that monitors each cell’s voltage and temperature, prevents overcharging or deep discharge, and balances the cells so they age evenly. Without a BMS, a single weak cell can drag down the whole pack or, worse, overheat and become a fire risk. The BMS also handles thermal protection, opening and closing cooling valves to keep the pack within a narrow temperature window for optimal performance and longevity.
Cooling the Battery Pack
Batteries generate heat during both charging and discharging, and managing that heat directly affects how long your pack lasts. Air cooling is the simplest approach: lightweight, cheap, and easy to maintain. But air has low thermal conductivity, which leads to uneven temperatures across the pack. Some cells run hotter than others, and that imbalance accelerates degradation.
Liquid cooling is more complex and expensive, but it keeps the pack significantly cooler and more uniform. Research comparing the two approaches found that at the same energy cost, liquid cooling keeps the hottest cell about 3°C cooler than air cooling. For a weekend project car that sees occasional use, air cooling may be perfectly adequate. For a daily driver or a pack over 30 kWh, liquid cooling is worth the added complexity.
Mating the Motor to the Drivetrain
This is where the mechanical engineering gets precise. Your electric motor needs to bolt up to the existing transmission so it can send power to the wheels through the original drivetrain. The connection is made through a custom adapter plate, essentially a machined aluminum plate that bridges two different bolt patterns and keeps the motor shaft perfectly aligned with the transmission input shaft.
The process starts with measuring the “backspacing” of both components. You measure from the mating face of the transmission bellhousing to the tip of its input shaft, then do the same on the motor side. Add those two numbers together plus about 2mm of clearance, and that’s the total spacing your adapter assembly needs to provide. Some combinations need only a motor plate and a gearbox plate. A Nissan Leaf motor to a Subaru transaxle, for instance, needs just 23mm of total spacing. A Leaf motor to a VW transaxle needs 60mm, requiring an additional spacer.
Alignment is critical. If the motor and transmission shafts aren’t concentric, you’ll put side loads on bearings that weren’t designed for them, leading to premature failure. One proven assembly technique is to stack the motor, adapter, and transmission vertically with all bolts left slightly loose, then spin the motor slowly. This lets the components self-center before you tighten everything down in a star pattern, gradually increasing torque in stages rather than fully tightening one bolt at a time.
Wiring for Standard Charging
If you want your converted car to charge at any public Level 2 station, you need a J1772 charging port. The SAE J1772 standard uses a five-pin connector: two AC power pins, a safety ground, and two signaling pins that let the car and charger communicate.
The Proximity Pilot pin tells the car’s charging system that a plug is physically connected and signals the vehicle’s control system to lock out the drivetrain so the car can’t move while plugged in. The Control Pilot pin handles the real negotiation. When you plug in, a resistor and diode between the Control Pilot and ground pins drop the charger’s 12-volt signal to 9 volts, confirming a proper electrical connection. The charger then sends a 1 kHz pulse-width-modulated signal that communicates how much current is available. A 16% duty cycle means 10 amps maximum, 25% means 16 amps, and 50% means up to 32 amps. Your onboard charger reads this signal and draws only what the station can safely provide.
Getting this communication right is essential. Without it, the charging station won’t deliver power. Most conversion builders use a pre-built J1772 inlet and charge controller module rather than wiring the signaling circuit from scratch.
High-Voltage Safety
A typical EV conversion runs at 96 to 400 volts DC, which is lethal. All high-voltage wiring should use orange-jacketed cables, following the same convention used by every major automaker so that anyone working on the car can immediately identify dangerous conductors. Your system needs a manual service disconnect: a clearly marked, brightly colored handle that physically breaks the high-voltage circuit. Place it somewhere accessible but protected, like under a seat or in the trunk area.
Before touching any high-voltage component during a build or repair, remove the service disconnect and wait several minutes for capacitors in the controller and charger to discharge. Then verify the system is de-energized with a multimeter rated for the pack’s voltage. If you read anything above 50 volts, stop and troubleshoot. Store the disconnect plug in your pocket while working so no one can accidentally re-energize the system. Insulated gloves rated for 1,000 volts are standard protective equipment for any high-voltage EV work.
Making It Road Legal
Registration requirements for a converted EV vary significantly by state. Most states treat a conversion as a modified vehicle: you keep the original VIN and title, update the fuel type with your DMV, and pass a state safety inspection. Some states require an emissions exemption letter since the car no longer has a tailpipe. A handful of states have specific EV conversion inspection requirements that check for proper high-voltage isolation, secure battery mounting, and functional braking.
Federal Motor Vehicle Safety Standards apply to manufacturers, not individuals modifying their own vehicles for personal use. You won’t need to certify your conversion to FMVSS, but the car still needs to meet your state’s safety inspection criteria, which typically cover lights, brakes, steering, tires, and windshield condition. If you’re building a vehicle from scratch rather than converting an existing one, the regulatory path is more complicated and varies by state, often requiring a specially constructed vehicle title.
Realistic Budget Breakdown
A complete conversion kit for a compact car, including motor, controller, charger, and a modest battery pack, starts around $14,000 to $16,000. A mid-size car with a larger pack runs $17,000 to $26,000. Tesla drivetrain swap packages start at $24,000 and offer more power and range but require more fabrication expertise. High-performance crate motor systems from companies like Revolt Systems range from $49,000 to $68,000 for turnkey powertrains.
On top of the kit, budget for the donor vehicle ($1,000 to $5,000 for a clean shell), the adapter plate and coupler ($500 to $2,000 depending on whether you machine your own or buy pre-made), battery boxes and mounting hardware ($500 to $1,500), a DC-DC converter to power the 12-volt accessories ($150 to $400), and miscellaneous wiring, contactors, fuses, and connectors ($500 to $1,000). A realistic all-in budget for a modest daily-driver conversion is $18,000 to $30,000 if you do the labor yourself. Shop labor, if you hire it out, can add $5,000 to $15,000 depending on complexity and local rates.