can a car engine be used in a plane

[AvaFitz]

No, a standard car engine cannot be safely or effectively used to power a conventional airplane. The fundamental differences in design, operation, and regulatory requirements make such a swap impractical and extremely dangerous. While there are experimental and ultralight aircraft that use modified automotive engines, these are significant engineering projects, not simple bolt-in operations.

The core issue lies in the different performance demands. An aircraft engine must be exceptionally reliable, produce consistent power at high altitudes, and have a high power-to-weight ratio. Car engines are designed for a completely different environment.

Key Differences Between Car and Aircraft Engines:

Characteristic	Car Engine	Aircraft Engine (Piston)	Why it Matters for Flight
Reliability & Redundancy	Can fail with minimal risk; pull over to side of road.	Failure can be catastrophic. Designed with extreme redundancy.	Safety is the absolute priority. There are no "pull over" options in the sky.
Power Output	Peak power at high RPM (e.g., 6,000 RPM).	Maximum power (often 75%) at a sustained, lower RPM (e.g., 2,500 RPM).	Planes need constant power for climb and cruise, not short bursts of acceleration.
Cooling System	Relies on a liquid cooling system with a radiator and fan.	Primarily air-cooled to avoid the complexity and weight of radiators/coolant.	A liquid cooling system is vulnerable to leaks and adds significant weight.
Weight	Often heavy with accessories like alternators, A/C compressors.	Designed to be as light as possible; every pound reduces payload.	Weight is a critical factor in aircraft performance and fuel efficiency.
Fuel Type & Carburetion	Uses gasoline; modern engines have fuel injection.	Often uses Avgas (100LL); carbureted engines are susceptible to carburetor icing.	Aircraft engines have specific systems to prevent icing, which can cause engine failure.
Regulatory Certification	Meets automotive EPA/DOT standards.	Requires rigorous FAA certification (FAR Part 33) for airworthiness.	Using an uncertified engine in a certified aircraft is illegal.

For experimental home-built aircraft, some enthusiasts use engines from Subaru or Rotax (which are specifically designed for aviation). However, these conversions require extensive modification, including adding a reduction gearbox to slow down the propeller speed, redesigning the cooling system, and ensuring absolute fuel and ignition system reliability. For any certified production airplane, using a car engine is not a legal or safe option.

[MacAdam]

As a guy who's tinkered with engines my whole life, I can tell you it's a bad idea. Sure, the basic concept of an internal combustion engine is the same, but that's where it ends. Think about it: if your car engine quits on the highway, you coast to the shoulder. If it quits at 5,000 feet, you have a serious problem. Plane engines are built to run smoothly for hours on end without a hiccup. A car engine just isn't built with that kind of rock-solid reliability in mind. It's about the right tool for the job.

[DeMartin]

While theoretically possible in very light, experimental aircraft, the challenges are immense. You'd need to solve for altitude-related power loss, prevent fuel vapors from forming at low atmospheric pressure, and completely redesign the engine's cooling. The propeller also needs to spin much slower than a car's crankshaft, requiring a heavy and complex reduction gearbox. The cost and effort to make a car engine remotely airworthy almost always far exceed just buying a proper aircraft engine.

[VanJeremiah]

The biggest hurdle isn't just engineering—it's legality. The Federal Aviation Administration (FAA) has strict certification rules (FAR Part 33) for aircraft engines. A car engine has zero certification for aerial use. Installing one in a standard, certified plane would instantly render it illegal to fly. Even for home-built kits, you'd face immense liability issues. It’s not just about whether it can work, but whether it’s approved to work in a context where safety is non-negotiable.

[CoreyFitz]

I look at it from an efficiency standpoint. Aircraft engines prioritize two things: reliability and power-to-weight ratio. Car engines are built for cost-effectiveness, emissions control, and a broad powerband for street driving. They are generally too heavy for their power output when you consider aviation needs. An aircraft piston engine might weigh 300 pounds but produce 300 horsepower. A car engine making the same power could weigh twice as much. In an airplane, that extra weight directly sacrifices fuel, payload, or range. The design philosophies are fundamentally opposed.