Lycoming O-320 vs O-360: Key Differences to Know Before Choosing

If you've spent any time shopping for a piston aircraft or planning an engine swap, you've probably landed square in the middle of the same debate: the Lycoming O-320 vs O-360. Both are legendary Lycoming engines. 

Both are four-cylinder, air-cooled, horizontally opposed powerplants that have been turning propellers across general aviation for decades. And yet, pilots argue about them on forums, at fly-ins, and in hangar corners like it's a matter of personal honor.

The truth is, these two engines are more alike than different — but the differences matter a lot depending on your airframe, your mission, and your budget. Whether you're building a homebuilt aircraft, upgrading a certified plane, or just trying to understand what's under your cowling, this guide breaks down everything you need to know about the Lycoming O-320 and O-360, side by side, in plain English.

Key Takeaways

The Lycoming O-320 vs O-360 debate comes down to power versus efficiency. The O-320 produces 150–160 hp and is lighter, simpler, and often more fuel-efficient at cruise. The O-360 makes 180 hp (or more in some variants) with greater displacement, stronger climb performance, and more flexibility for heavier airframes. Neither engine is universally better — the right choice depends on your aircraft type, intended use, and total cost of ownership.

At Flying411, we make it easier to find aircraft powered by engines that match your mission — whether you're after the economy of the O-320 or the muscle of the O-360.

A Little Background: Where These Engines Came From

Lycoming has been building aircraft engines in Williamsport, Pennsylvania, for well over a century, and its four-cylinder family is one of the most proven engine lineages in all of general aviation.

The O-320 entered the scene in 1953 and quickly became the go-to powerplant for light trainers and economy aircraft. It shares its 3.875-inch stroke with the smaller O-235 and O-290 engines but uses a larger bore to produce more power. The 0-320 family grew to include dozens of variants — Lycoming certifies well over 50 distinct O-320 models — covering everything from basic carbureted trainers to fuel-injected aerobatic machines.

The O-360 followed a few years later, stretching the same basic architecture with a longer 4.375-inch stroke and the same 5.125-inch bore to produce 360 cubic inches of total displacement. The result was a stronger, heavier engine that made a genuine 180 hp in most configurations. The O-360 engine family is similarly vast, with more than 50 certified variants of its own.

Fun Fact: The Lycoming O-360 forms the foundation for the six-cylinder O-540, which is essentially a 360 with two extra cylinders bolted on. Same bore, same stroke — just more of them.

Both engines are direct-drive, meaning the crankshaft turns the propeller at the same speed as the engine. This simplicity is a big part of their appeal and longevity.

Displacement and the Displacement Myth

Here's where a lot of pilots get confused. The names "O-320" and "O-360" refer to displacement in cubic inches — 320 cubic inches versus 360 cubic inches. That 40-cubic-inch difference comes entirely from a longer stroke on the 360.

The bore on both engines is identical: 5.125 inches. What changes is the piston travel. The O-360's piston travels 4.375 inches compared to 3.875 inches in the O-320. That longer travel is what gives the 360 its extra squeeze — and its extra weight.

Good to Know: Bigger displacement doesn't always mean more power per drop of fuel. At the same cruising speed, a properly managed O-360 and a properly managed O-320 can have surprisingly similar fuel consumption because power required to push the plane through the air stays the same.

This is one of the most misunderstood points in the O-320 vs O-360 debate. The O-360 burns more fuel primarily because it's making more power — not because it's inherently inefficient.

Horsepower: The Number Everyone Asks About

The O-320 family is rated at 150 or 160 hp depending on the variant. Most common versions produce 160 hp at 2,700 rpm. Lower compression models (like the C series with 7.0:1 compression ratio) top out at 150 hp.

The 0-360 is typically a 180 hp engine at 2,700 rpm, though the family spans a surprisingly wide range. Some variants run as low as 145 hp for helicopter applications (the Robinson R22 uses a detuned O-360), while the turbocharged TIO-360 and IO-360 variants can push well beyond 180 hp.

Understanding the Horsepower Gap

That 20 hp gap between a 160 hp O-320 and a 180 hp O-360 translates to real-world differences — but not always where pilots expect.

• Climb rate improves noticeably with the extra power, especially at gross weight
• Cruise speed increases by roughly 5–10 mph in most airframes
• Takeoff distance shrinks, which matters on short or soft fields
• High-altitude performance benefits from the extra power reserve

The gap matters most during departure and climb. In level cruise, the two engines often end up at similar throttle settings and similar fuel burns to maintain the same speed.

Pro Tip: If most of your flying is cruise-heavy cross-country work, the O-320's efficiency story is more compelling than the horsepower numbers suggest. If you're hauling two adults and luggage out of a short strip, the O-360 earns its keep.

Parallel Valve vs Angle Valve: A Detail That Really Matters

Both engine families come in parallel valve and angle valve (sometimes called angle valve or narrow-deck) configurations — and this distinction affects cost, maintenance, and even reliability.

Parallel valve engines have intake and exhaust valves running parallel to the cylinder axis. They're simpler, lighter, and generally less expensive to overhaul. The vast majority of O-320 engines and the most common O-360 variants (like the A and C series) are parallel valve.

Angle valve engines tilt the valves for a more efficient combustion chamber shape. They make more power for their displacement but come with a cost premium on parts. Cylinder replacement for angle valve heads can run significantly more than for parallel valve designs — in some cases more than double.

Heads Up: If you're comparing a standard O-360-A series (parallel valve) to an IO-360 angle valve variant, you're not just comparing carbureted vs fuel-injected — you're also comparing very different maintenance cost profiles. Always check valve configuration before buying.

The most celebrated bulletproof Lycoming engines among overhaulers tend to be the parallel valve O-360 models — specifically the A and C series carbureted variants. Their combination of robust cases, simple design, and de-rated power (180 hp from a 360-cube engine is genuinely relaxed) allows some well-maintained examples to run thousands of hours beyond their official TBO.

Carbureted vs Fuel Injected: O vs IO

Both the O-320 and O-360 families come in carbureted ("O") and fuel injection versions ("IO"). The carburetor is simpler and easier to start in cold weather. Fuel injection — specifically the continuous-flow system used by Lycoming — offers better fuel distribution, the ability to run efficiently lean of peak, and no carb ice concerns.

The IO-360 in particular is one of the most popular injected Lycoming variants, appearing in aircraft like the Piper Arrow, Beechcraft Musketeer, and countless homebuilts.

For a deeper look at how Lycoming fits into the broader engine landscape, check out this comparison of Continental vs Lycoming aircraft engines.

The Hot-Start Tradeoff

Fuel injection comes with one well-known quirk: hot starts can be finicky. Vapor lock in the fuel injector lines after shutdown can make restarting feel like a ritual. Most experienced IO pilots develop a reliable procedure, but it's worth being aware of if you're transitioning from a carbureted engine.

Quick Tip: On hot starts with an injected Lycoming, the standard technique involves cracking the throttle, mixture off, and cranking to clear the lines before lighting it up. Ask a CFI familiar with your specific variant for the exact procedure.

The Great Engine Mount Question: Conical vs Dynafocal

Both the O-320 and O-360 come in conical and dynafocal mount configurations, and mixing these up is one of the most common — and expensive — mistakes in engine shopping.

Dynafocal mounts use rubber isolators positioned so they point toward the engine's center of gravity. They do an excellent job absorbing vibration. Conical mounts are simpler and less effective at vibration isolation but work fine in many applications.

The dynafocal mounts add about 10 pounds to the overall installation and require specific engine mount hardware from the airframe manufacturer. A dynafocal O-360 cannot simply bolt onto an engine mount designed for a conical O-320 without significant modification.

Keep in Mind: When shopping for a used engine, always verify the mount type against your airframe's engine mount before purchase. An otherwise perfect O-360 is useless if it's the wrong mount configuration for your airplane.

What the Lycoming O-320 vs O-360 Decision Looks Like in the Real World

Here's where the rubber meets the runway — how does this engine choice play out across real aircraft and real use cases? These are the key factors that should drive your decision:

1. Your Aircraft's Gross Weight

Heavier airframes benefit more from the O-360. A Piper Archer carrying four adults and baggage genuinely needs that 180 hp. A light two-seat trainer doing pattern work? A 160 hp O-320 is plenty.

2. The Field You Fly From

Short runways, high density altitude, or regular operations at elevation make the O-360 more valuable. The extra power reserve on departure can matter. The backcountry community — Super Cubs, Carbon Cubs, and similar bush planes — has famously debated 160 vs 180 hp for years, and the answer often comes down to the specific strip.

If you're comparing engines for a bush or backcountry build, this breakdown of the Lycoming O-235 vs Rotax 912 can help frame the wider options available.

3. Total Weight of the Installation

The engine itself may weigh only about 7–15 pounds more for the O-360, but the full package — heavier prop, dynafocal mounts, larger exhaust, and possibly a heavier fuel pump — can push the weight difference to 30–40 pounds in some configurations. For weight-critical builds, this matters.

4. Budget and Overhaul Cost

Both engines have a typical TBO of around 2,000 hours. Overhaul costs vary significantly by variant and shop, but the O-360 generally costs somewhat more to overhaul, particularly in angle-valve configurations. Parallel-valve O-360 overhauls are quite competitive with O-320 work.

Fun Fact: Well-maintained parallel-valve O-360s — particularly those used in flight training — have been known to run well past 3,000 hours before needing overhaul, thanks to the engine running relaxed at only 180 hp from a 360-cube design.

Flying411 can help you evaluate the total cost picture of any aircraft purchase, engine included.

5. Fuel Economy and Avgas Compatibility

Lower compression ratio variants of both engines (particularly the older C-series O-320 and some O-360 D-series) are approved for lower-grade fuel, which can be meaningful as the future of avgas evolves. Higher-compression versions — those targeting 100LL — are common in newer builds and provide more power but less fuel flexibility.

At cruise, the O-320 typically burns in the range of 7–8 gallons per hour in most installations. The O-360 may run 8–10 GPH at higher power settings, though throttled to the same cruise speed as an O-320, consumption tends to converge.

6. Ignition: Dual Magneto vs. Two Singles

Most O-320 and O-360 engines use two independent magnetos for redundancy. Some variants use a dual magneto — a single unit containing both ignition systems — which simplifies the accessory case but means one failure takes out both magneto circuits simultaneously. Knowing which your engine uses matters for preflight planning and troubleshooting.

7. The Homebuilt and Experimental Market

For homebuilt aircraft builders, both engines are popular choices. The O-360 dominates in higher-performance kits like the Van's RV-7 and RV-8, while the O-320 is preferred in lighter, more efficient builds like the RV-9A. The ECI (Engine Components International) and Superior aftermarket cylinder options are available for both, which gives builders flexibility on overhaul costs without sacrificing reliability.

Builders considering alternative powerplants should also look at how the Rotax 914 stacks up against the Rotax 915 and the Rotax 915iS vs 916iS comparison for a broader perspective.

8. The Aerobatic Variants

Both families have dedicated aerobatic versions. The AEIO-320 and AEIO-360 (both part of Lycoming's aerobatic lineup) swap the standard sump for an inverted oil system, allowing sustained negative-g flight. These are popular in competition aerobatic aircraft and advanced upset training programs. The oil system redesign also affects the crankcase breather path, so they are not interchangeable with standard variants without modification.

Looking at smaller Lycoming options for lighter aerobatic trainers? See this comparison of the Continental O-200 vs Lycoming O-235.

9. The O-320-H2AD: The One to Research Carefully

Worth a specific mention: the O-320-H2AD, installed in Cessna 172Ns built from roughly 1977 to 1980, developed a reputation for camshaft and tappet problems due to a redesigned hydraulic lifter. Many of these engines have received updates and airworthiness directive compliance over the decades, and well-maintained examples can be perfectly solid — but if you're looking at a late-1970s Skyhawk, check the engine serial number carefully and verify all STC and AD compliance with your A&P.

Why It Matters: Not all O-320 engines are created equal. With over 50 certified variants in the family, the model suffix tells you a huge amount about compression, mount type, carburetor location, and ignition. Always get the full model designation before shopping or comparing.

10. The Cessna and Piper Connection

The O-320 is most closely associated with the Cessna 172 (particularly pre-2000 models) and the Piper Cherokee 140. The O-360 powers the Piper Archer (PA-28-181), the Piper Arrow, and the later Cessna 172SP. This is why these engines dominate the used aircraft market — millions of hours of fleet experience back up their reputations.

Flying411 can connect you with aircraft across a range of power plants and price points — start browsing today to find a plane that matches your mission.

Side-by-Side Spec Comparison

Making the Call: Which Engine Is Right for Your Mission?

If weight, simplicity, and cruise efficiency are your top priorities — and your airframe is rated for 150–160 hp — the O-320 is a rock-solid choice that will serve you well for decades with proper care.

If you need more climb performance, carry heavier loads, fly from challenging strips, or want the power reserve that 180 hp provides, the O-360 earns every pound it adds to the nose.

The honest truth: the parallel-valve versions of both engines are among the most reliable piston aircraft powerplants ever built. Choosing between them is less about which is "better" and more about which one fits your specific mission, your specific airframe, and your specific budget.

Ready to find an aircraft that matches your engine preference? Visit Flying411 and start your search today — we make aircraft ownership approachable, one great match at a time.

Conclusion

The Lycoming O-320 vs O-360 debate has been running for decades because both engines genuinely deserve their place in general aviation. The O-320 is a smooth, efficient, proven performer that handles the vast majority of light-plane missions with confidence. The O-360 is a stronger, more versatile engine that opens doors for heavier payloads, higher-altitude performance, and demanding flying environments. Neither is the wrong answer — the wrong answer is picking one without fully understanding how it fits your airplane and how you fly.

Whatever engine ends up under your cowling, fly it regularly, maintain it well, and don't let it sit. The best thing you can do for any Lycoming is keep the oil warm and the hours moving.

When you're ready to find an aircraft with the right engine for your goals, Flying411 is your starting point for making smart, informed aviation decisions.

Frequently Asked Questions

What is the main difference between the Lycoming O-320 and O-360?

The primary difference is displacement and power. The O-320 displaces 320 cubic inches and produces 150–160 hp, while the O-360 displaces 360 cubic inches and typically produces 180 hp. The longer stroke of the O-360 accounts for the additional displacement.

Can I swap an O-320 for an O-360 in my Cessna 172?

In many cases, yes — there are approved STCs that allow the O-360 to be installed in aircraft originally equipped with the O-320. However, the installation requires compliance with the specific STC, engine mount compatibility verification, and often a new or modified propeller. Always consult a licensed A&P and review the applicable STC documentation before any engine swap.

Which engine is cheaper to overhaul — the O-320 or O-360?

Costs vary by shop, variant, and core condition, but the O-320 is generally somewhat less expensive to overhaul than the O-360 for comparable parallel-valve versions. Angle-valve O-360 variants (used in higher-horsepower IO-360 applications) carry notably higher parts costs than parallel-valve versions of either family.

How much does an O-360 weigh compared to an O-320?

The weight difference between similarly equipped parallel-valve versions of both engines is often only 7–20 pounds at the engine alone. When the full installation is factored in — including propeller, engine mount hardware, and exhaust — the total weight difference can reach 30–40 pounds depending on specific configurations.

Are Lycoming O-320 and O-360 engines compatible with mogas or unleaded fuel?

Some lower-compression variants of both engines are approved for automotive gasoline (mogas) under specific STCs and conditions. Higher-compression versions are designed for 100LL avgas. As the aviation industry moves toward unleaded alternatives, always check the current approved fuel grades for your specific engine model and any applicable STCs or airworthiness directives.