Rotax 915iS vs 916iS: A Detailed Comparison

Picking an engine for your airplane is one of the biggest decisions you'll make as a pilot or aircraft builder. The Rotax 915iS and 916iS sit at the top of the light aircraft engine world right now. Both come from the same Austrian company, both use turbocharged technology, and both fit in many of the same airplane kits. Rotax has dominated this market for decades. 

In fact, back in 1998, Rotax outsold all other aero engine manufacturers combined in the light aircraft class. That success came from building engines pilots trust. But these two engines aren't twins. One costs more money upfront. The other lasts longer before needing major work. One gives you extra power when you need it most. The other has been proven in hundreds of aircraft over several years. 

Understanding what makes each engine special helps you choose the right one for your flying plans and budget.

Key Takeaways

The Rotax 915iS and 916iS are both excellent turbocharged aircraft engines, but they serve different needs. The 915iS produces 141 horsepower at takeoff and costs around $43,700, with a 1,200-hour time between overhaul. The 916iS delivers 160 horsepower at takeoff and costs about $51,400, but it runs for 2,000 hours before needing overhaul. Both engines make nearly the same continuous power during cruise flight (around 135-137 hp). The 916iS has a stronger crankshaft, better cooling, and uses special synthetic oil. It costs more to buy but saves money over time because it lasts longer. If you want proven technology and lower upfront cost, choose the 915iS. If you want maximum takeoff power and the longest time between overhauls, choose the 916iS.

What Is a Rotax Aircraft Engine?

Rotax engines come from Austria and power more than half of all light sport and experimental aircraft flying today. The company started making engines for snowmobiles and motorcycles before moving into aviation. They bring that automotive-style technology to airplanes.

A Rotax aircraft engine looks different from the traditional engines you might see on a Cessna or Piper. Most aviation engines are big, air-cooled powerplants built the same way they were 70 years ago. Rotax engines use liquid cooling for the cylinder heads (water jackets keep them cool) plus air cooling for the rest. This combination helps them run at higher power levels without overheating.

How Rotax Engines Work

These engines are small but mighty. They use only 1,352 cubic centimeters of displacement (about 82.5 cubic inches). That's tiny compared to most aircraft engines. To make good power from such a small package, they spin fast. Really fast. The crankshaft turns at 5,800 RPM during takeoff. Compare that to a typical Lycoming engine that turns around 2,700 RPM.

Because the engine spins so fast, it needs a gearbox to slow down the propeller. The propeller spins at a much slower speed than the engine itself. This gearbox has a 2.54:1 reduction ratio. For every 2.54 times the engine turns, the propeller turns once.

The Modern Rotax Advantage

Newer Rotax models like the 915iS and 916iS use electronic fuel injection. A computer controls exactly how much fuel goes into each cylinder. This makes them very fuel-efficient compared to older carbureted engines. They also have FADEC, which stands for Full Authority Digital Engine Control. The computer manages the engine automatically, adjusting things like fuel mixture and timing without you touching any controls.

The 914 was Rotax's first turbocharged model. It made 115 horsepower and showed that small turbocharged engines could work well in aircraft. The 915iS and 916iS take that idea even further with intercoolers and modern electronics.

Why Engine Choice Matters for Pilots

Your engine choice affects everything about your flying experience. It changes how your airplane performs, how much you spend on fuel, and how often you'll be writing checks for maintenance.

Performance on Takeoff Day

Takeoff power makes the biggest difference when you're getting off the ground. Those first few minutes after you release the brakes are when you need every bit of power available. An engine with more takeoff power helps you clear obstacles faster and gives you more safety margin if something goes wrong.

Think about taking off from a short mountain airstrip on a hot summer day. The air is thin. Your airplane is heavy with fuel and passengers. Those extra 19 horsepower in the 916iS can mean the difference between clearing the trees comfortably and white-knuckling it.

The Long-Term Cost Picture

TBO stands for Time Between Overhaul. It tells you how many hours you can fly before the engine needs to come apart for inspection and rebuilding. A higher TBO means fewer major maintenance events over the life of your airplane. That saves money. It also means less downtime when your airplane sits in the shop instead of flying.

Let's say you fly 100 hours per year. With a 1,200-hour TBO on the 915iS, you'll need an overhaul after 12 years. With the 2,000-hour TBO on the 916iS, you can fly 20 years before that big maintenance event. One overhaul can cost $30,000 or more, so stretching out that timeline matters.

Daily Flying Comfort

The amount of continuous power your engine makes affects your everyday flying. Cruise power is what you use for 90% of your flight time. Both the 915iS and 916iS make almost the same continuous power (around 137 hp). This means they fly almost identically once you're up and cruising.

Fuel efficiency matters too. Both engines have an "Eco mode" that runs leaner mixtures when you're not at full throttle. This saves fuel compared to older carbureted engines that always run rich mixtures. Pilots report fuel burns of 6-8 gallons per hour in cruise, which is excellent for this power level.

Meet the 915iS and the 916iS

These two engines share the same family tree but have important differences. Understanding where each one comes from helps you see why they're built differently.

The Rotax 915iS Story

The Rotax 915iS appeared at the big Oshkosh airshow in July 2015. Pilots had been asking for a more powerful Rotax for years. The 912iS made 100 horsepower, and the turbocharged 914 made 115 horsepower. Aircraft designers wanted something stronger for four-seat airplanes and high-performance two-seaters.

Rotax answered with the 915iS. It uses the same basic engine block as the 912iS but adds a turbocharger and an intercooler. The turbocharger forces more air into the engine, and the intercooler cools that compressed air before it enters the cylinders. Cooler air is denser, which means more power.

This engine earned certification in 2017 and has been flying in hundreds of aircraft since then. It powers popular kit planes like the Sling TSi, Kitfox, Bristell, and Progressive Aerodyne Searey. The 915iS weighs just 185 pounds but delivers 141 hp for takeoff. That's an incredible power-to-weight ratio.

The Rotax 916iS Arrives

Rotax unveiled the Rotax 916iS at the Sun 'n Fun airshow in March 2023. They called it "The Impossible Engine" because it seemed impossible to get more power from the same size package without sacrificing reliability.

The 916iS looks almost identical to the 915iS on the outside. It bolts right into the same engine mounts. But inside, nearly everything got stronger. The crankshaft is beefier. The crankcase has reinforcements around the main bearings. The oil system has extra squirters to spray more cooling oil on critical parts. Even the oil itself is different—a fully synthetic formula that can handle higher temperatures and pressures.

The result is 160 hp for takeoff and a 2,000-hour TBO right from the start. That TBO number is huge. Most aircraft engines start at 1,200 or 1,500 hours. Rotax had enough confidence in the 916iS design to promise 2,000 hours on day one.

What They Share

Both engines use the same displacement (1,352 cc), the same bore and stroke, and the same gearbox reduction ratio. Both run on multiple fuel types—regular automotive gasoline (mogas), 100LL avgas, or even ethanol blends up to E10. This fuel flexibility is valuable in areas where avgas is expensive or hard to find.

Both have dual-channel electronic fuel injection and dual electronic ignition. If one channel fails, the other keeps running. Both maintain full takeoff power up to 15,000 feet of altitude, which is remarkable. A normally aspirated engine loses about 3% of its power for every 1,000 feet of altitude gain. These turbocharged engines don't.

Rotax 915iS vs 916iS: Key Differences Pilots Should Know

Now we get into the details that separate these two engines. Some differences jump out immediately. Others only matter in specific situations. Understanding each difference helps you make the right choice for your airplane.

Power Output: Where the Numbers Tell the Story

The Rotax 915iS produces 141 horsepower at maximum power. You can use this full power for five minutes during takeoff and initial climb. After those first five minutes, you reduce the throttle to the continuous power setting of 135 hp. This is the power level you'll use for climbing to cruise altitude and for the entire rest of your flight.

The Rotax 916iS delivers 160 hp at maximum power for those same five minutes of takeoff and climb. Then you pull back to 137 hp for continuous operation. That's 19 extra horses when you push the throttle forward for takeoff. But once you settle into cruise flight, you're only getting 2 extra horsepower compared to the 915iS.

These numbers matter most during different phases of flight. During takeoff, every bit of extra power helps. You accelerate faster down the runway. You lift off sooner. Your climb rate increases. A typical installation might see climb rates improve by 200-300 feet per minute with the 916iS compared to the 915iS.

Think about taking off from a runway at 6,000 feet elevation on a summer afternoon. The temperature is 85 degrees. The density altitude might be 9,000 feet or higher. In these conditions, engines lose significant power. That extra 19 horsepower in the 916iS gives you more safety margin when the air is thin and hot.

But once you're cruising along at 8,000 or 10,000 feet, both engines perform almost identically. The 2-horsepower difference at continuous power means you might see 2-3 knots difference in cruise speed. Most pilots won't even notice that small change. Your fuel burn will be nearly the same. Your range will be nearly the same.

RPM Limits: How Fast These Engines Spin

Both engines share the same RPM limits. Maximum power happens at 5800 RPM for those five minutes of takeoff power. Continuous power runs at 5500 RPM. These are crankshaft speeds, not propeller speeds.

Compare this to older aviation engines. A typical Lycoming or Continental runs around 2,700 RPM at full power. Rotax engines spin more than twice as fast. This high RPM allows them to make good power from a small displacement.

The high crankshaft speed creates challenges. Propellers don't work well at these speeds. A propeller tip moving too fast creates noise and loses efficiency. That's why both engines use a reduction gearbox. This gearbox slows the propeller down to a reasonable speed.

The gearbox has a 2.54:1 reduction ratio. When the engine crankshaft spins 2.54 times, the propeller spins once. So at 5800 RPM engine speed, the propeller turns at about 2,283 RPM. At 5500 RPM engine speed, the propeller spins at roughly 2,165 RPM. These propeller speeds are much more reasonable and efficient.

Time Between Overhaul: The 800-Hour Difference

TBO stands for Time Between Overhaul. This number tells you how many flight hours the engine can run before it needs major maintenance. The TBO difference between these engines is huge and affects your long-term costs significantly.

The 915iS has a 1,200-hour TBO. The 916iS has a 2,000-hour TBO. That's 800 extra hours of flying before you need to tear the engine down for inspection and rebuilding. In percentage terms, the 916iS gives you 67% more time between overhauls.

Rotax has been very clear about one important fact: they will not extend the 915iS TBO to match the 916iS. The 915iS will stay at 1,200 hours. The internal improvements in the 916iS cannot be added to existing 915iS engines. The stronger parts work together as a complete system. You can't just swap in one upgraded component and expect the same reliability.

Let's look at what TBO means in real flying time. Say you fly 100 hours per year, which is typical for an active recreational pilot. With the 915iS at 1,200-hour TBO, you'll reach overhaul time in 12 years. With the 916iS at 2,000-hour TBO, you can fly for 20 years before that major maintenance event.

If you fly more often, the timeline shortens. A pilot logging 150 hours per year reaches TBO in 8 years with the 915iS or 13.3 years with the 916iS. A flight school or commercial operator running 500 hours annually hits TBO in just 2.4 years with the 915iS or 4 years with the 916iS.

Understanding when to overhaul an aircraft engine: hours, signs, and safety tips helps you plan for this major expense. Most owners start budgeting for overhaul costs from the day they buy the engine.

Internal Construction: What Changed Inside

Open both engines side by side and you'll see the improvements. The 916iS crankshaft uses upgraded materials and has beefier dimensions in critical areas. The crankshaft takes enormous stress during operation. Every power stroke tries to twist it. Every cylinder firing hammers on it. The strengthened crankshaft in the 916iS handles these loads better over time.

The crankcase received reinforcements too. Extra material surrounds the main bearing supports. These areas hold the crankshaft in place and take constant pounding during operation. The added strength helps the 916iS last longer under hard use.

The oil system got significant updates. The 916iS has additional oil squirters inside the crankcase. These are like little spray nozzles that shoot streams of oil onto critical parts. The extra oil flow helps cool the pistons, crankshaft, and bearings. Better cooling means longer life and more reliability.

The oil itself changed. The 916iS requires a fully synthetic 5W50 oil specially formulated for this engine. The old Aeroshell Sport Plus 4 oil that works perfectly in the 914, 912, and 915iS engines can't handle the higher temperatures and pressures inside the 916iS. The new synthetic oil costs more per quart but provides essential protection.

The cooling system received upgrades across the board. The 916iS has a larger intercooler compared to the 915iS. The intercooler cools the compressed air coming from the turbocharger before it enters the cylinders. Cooler intake air is denser, which means more power. It also reduces the chance of detonation, which can destroy an engine quickly.

The oil radiator grew larger too. More surface area means better heat dissipation. The engine stays cooler during climbs and hot-weather operations. Cooler temperatures throughout the engine contribute to longer life.

Even the exhaust system changed. The 916iS uses an updated muffler design with lower back-pressure. This helps the turbocharged system work more efficiently. There's also a new after-muffler that meets stricter European noise regulations. While noise rules matter less in the United States, the improved exhaust system contributes to better overall performance.

Weight: Almost No Penalty

You might expect all these improvements to add serious weight. They don't. The 915iS weighs 185 pounds dry (without oil, coolant, or accessories). The 916iS weighs 189 pounds dry. That's a difference of only 4 pounds.

This minimal weight gain is impressive engineering. Rotax didn't just make everything heavier and call it stronger. Their engineers carefully analyzed each part and strengthened only the areas that needed it. They removed material from areas that didn't need extra strength. The result is an engine that's stronger where it counts without becoming a boat anchor.

For comparison, a typical Lycoming O-320 engine (160 hp) weighs around 280 pounds. Both Rotax engines save roughly 90-95 pounds compared to traditional aircraft engines. This weight savings lets you carry more fuel, more passengers, or more baggage. In a light sport aircraft operating under weight limits, those 90 pounds might mean the difference between legally carrying two adults with full fuel or having to reduce fuel load.

Price Comparison and Long-Term Value

The 915iS currently sells for approximately $43,700. The 916iS costs around $51,400. That's a difference of $7,700 upfront. Looking at this price difference alone, the 915iS seems like the obvious choice to save money.

But aircraft ownership costs go far beyond the initial purchase. You need to consider the total cost of ownership over the engine's lifetime. The longer TBO on the 916iS changes the math significantly.

An engine overhaul typically costs between $25,000 and $35,000 depending on what needs replacing and which shop does the work. Some owners choose to buy a new engine instead of overhauling their old one, since the price difference is relatively small and you get a fresh engine with a full warranty.

Let's use $30,000 as an average overhaul cost. With the 915iS at 1,200-hour TBO, you're setting aside $25 per hour for engine reserves ($30,000 divided by 1,200 hours). With the 916iS at 2,000-hour TBO, you only need to save $15 per hour ($30,000 divided by 2,000 hours).

That $10 per hour difference adds up fast. Fly 100 hours per year and you save $1,000 annually in engine reserves. Fly 150 hours per year and you save $1,500 annually. Over a 10-year ownership period at 100 hours per year, that's $10,000 in savings. This completely offsets the higher purchase price.

The 916iS also holds value better at resale time. Buyers pay more for engines with more time remaining before overhaul. An airplane with a 916iS at 800 hours (1,200 hours remaining) is worth more than one with a 915iS at 800 hours (only 400 hours remaining).

Propeller Compatibility: A Key Practical Difference

The 915iS works with both Airmaster and MT Propeller constant-speed propellers. The 916iS only works with MT Propeller systems. This limitation matters more than you might think.

Many popular kit aircraft like the Sling TSi and Kitfox come with specific propeller systems designed into the firewall-forward kit. If your chosen aircraft uses an Airmaster propeller, you'll need to stick with the 915iS or switch to an MT propeller (which requires different mounting hardware and may need engineering approval).

Constant-speed propellers automatically adjust their blade angle to maintain the correct RPM as conditions change. During takeoff, the blades are at a fine pitch (low angle) to move lots of air and generate thrust. During cruise, the blades move to a coarse pitch (higher angle) for efficiency. The propeller governor handles all this automatically.

Both Airmaster and MT make excellent propellers. The choice between them often comes down to price, availability, and what your aircraft kit includes. MT propellers tend to cost slightly more but have a strong reputation for quality and customer support. Airmaster propellers offer good value and work well in many installations.

If you're building an experimental aircraft, you have flexibility in choosing propellers. If you're buying a factory-built light sport aircraft, the manufacturer has already made this decision for you. Understanding propeller compatibility before ordering your engine prevents expensive surprises later.

Fuel Flexibility: Both Engines Drink Multiple Fuels

Both the 915iS and 916iS run on multiple fuel types. You can use regular automotive gasoline (mogas), 100LL low-lead avgas, unleaded automotive premium gas, or even fuel blends containing up to 10% ethanol (E10). This flexibility gives you options at the fuel pump.

In many areas, automotive gas costs significantly less than avgas. Flying on mogas can save you $2-3 per gallon. Over a year of flying, those savings really add up. Some remote airports only have automotive gas available, so the ability to use it keeps you flying when avgas isn't around.

The engines need fuel meeting minimum octane ratings: MON 85, RON 95, or AKI 91. Most regular automotive gasoline meets these specs easily. The electronic engine management system adjusts automatically for different fuels. You don't need to change any settings or flip any switches.

One caution: ethanol absorbs water and can corrode some fuel system parts over time. If you regularly use E10 fuel, pay extra attention to your fuel system during annual inspections. Many pilots prefer to use pure gasoline (E0) when available to avoid potential ethanol-related issues.

Altitude Performance: Full Power Where Others Fade

Both engines maintain full takeoff power up to 15,000 feet of altitude. This is called the critical altitude. Below 15,000 feet, the turbocharger provides enough boost to compensate for thin air. Above 15,000 feet, the turbocharger can't maintain full boost and power starts dropping off.

This high-altitude capability sets these engines apart from normally aspirated powerplants. A non-turbocharged engine loses about 3% of its power for every 1,000 feet of altitude gain. By 10,000 feet, a normally aspirated engine making 160 hp at sea level only produces about 112 hp. The turbocharged Rotax engines still make full power at 10,000 feet.

This matters for mountain flying and for flying across the western United States. Field elevations of 5,000-7,000 feet are common. On a hot day, density altitude might reach 10,000 feet or higher. Having full power available makes takeoffs safer and climbs faster in these conditions.

The service ceiling (maximum altitude the aircraft can reach) is 23,000 feet for both engines. Few light aircraft actually fly this high, but it's nice to know the engines can get you there if needed. Most pilots cruise between 8,000 and 12,000 feet, well within the engines' comfort zone.

Understanding your engine's requirements for an aircraft registration number and tail rules helps ensure your airplane meets all regulatory requirements, including proper documentation of engine specifications and performance capabilities.

Which Engine Is Better for Your Flying Style?

The right engine depends on how you fly, what you fly, and what matters most to you. Let's look at different situations.

Budget-Conscious Builders

If minimizing upfront costs is your priority, the 915iS wins. That $7,700 price difference buys a lot of avionics or interior work for your airplane. The 915iS has proven itself reliable in service for many years. Hundreds of aircraft are flying with these engines right now, racking up tens of thousands of flight hours.

Remember that if you're building an experimental amateur-built aircraft, the TBO is just a recommendation. You're not legally required to overhaul at 1,200 hours. Many owners do condition-based maintenance instead, running their engines longer if oil analysis and compression tests look good.

High-Performance Seekers

If you want maximum performance, especially for takeoff and climb, the 916iS delivers. That extra 19 horsepower at takeoff makes a real difference. Think about these scenarios:

Flying in the western mountains where density altitude regularly exceeds 8,000 feet. Taking off from short backcountry strips with obstacles to clear. Climbing through turbulence quickly to reach smooth air. Getting to cruise altitude faster to save fuel and time. In all these situations, the 916iS gives you an edge.

Long-Term Operators

If you plan to own and fly your airplane for many years, the 916iS makes economic sense. The longer TBO means fewer overhaul events. Each overhaul costs money and time. Your airplane sits in the shop for weeks or months while the engine is apart. That's time you're not flying.

The 2,000-hour TBO also helps resale value. When you eventually sell your airplane, buyers pay more for engines with time remaining before overhaul. An engine at 500 hours with 1,500 hours remaining is much more valuable than one at 900 hours with only 300 hours remaining.

Flight Schools and Commercial Operators

Commercial operations put heavy use on engines. A busy flight school might run 500-800 hours per year on each airplane. At that rate, a 1,200-hour TBO means overhauling every 1.5 to 2.4 years. A 2,000-hour TBO stretches that to 2.5 to 4 years. Fewer overhauls mean lower operating costs and less downtime.

The 916iS also qualifies for Rotax Care, an extended warranty program that can cover the engine up to TBO. For commercial operators, this warranty provides valuable financial protection.

Weekend Pilots and Recreational Flyers

If you fly 50-75 hours per year for fun, either engine works great. At that rate, you'll reach TBO in 16-24 years with the 915iS or 27-40 years with the 916iS. Both timeframes are longer than most people own an airplane.

Your decision might come down to which propeller system you prefer or which engine is available when you're ready to order. Lead times vary, and sometimes one engine is in stock while the other has a waiting period.

Conclusion

The Rotax 915iS and 916iS represent the cutting edge of light aircraft engine technology. Both deliver excellent power-to-weight ratios, impressive fuel efficiency, and the ability to maintain full power at high altitudes. The 915iS offers proven reliability at a lower purchase price. The 916iS provides maximum power and the longest time between overhauls in the Rotax lineup.

Your choice comes down to priorities. Value upfront savings and proven track record? Go with the 915iS. Want the latest technology with best long-term economics? Choose the 916iS. Either way, you're getting a modern, efficient, turbocharged engine that will serve you well for many years of flying.

Ready to dive deeper into aircraft ownership topics? Visit Flying411 for more detailed guides on engines, maintenance, and everything else you need to know about keeping your airplane in the air.

Frequently Asked Questions

Can I upgrade my 915iS to 916iS specifications later?

No, Rotax has confirmed that the 916iS upgrades cannot be retrofitted to existing 915iS engines. The improvements include different internal parts like the crankshaft, crankcase reinforcements, and oil system that must be installed during manufacturing.

Do both engines burn the same amount of fuel?

The 916iS actually uses 10-20% less fuel than the 915iS at the same power settings because of improved engine management software. Both engines have excellent fuel economy compared to older designs, typically burning 6-8 gallons per hour in cruise.

How long does an engine overhaul take?

A typical Rotax overhaul takes 4-8 weeks depending on parts availability and shop workload. Some owners choose to buy a new engine instead since the cost difference between overhaul and new is relatively small, which gets you flying again faster.

What maintenance do these engines need between overhauls?

Both engines require oil changes every 100 hours or annually, rubber hose replacements every 5 years, gearbox inspection at specific intervals, and spark plug replacement every 200 hours. The electronic systems make routine maintenance simpler than older carbureted engines.

Will either engine work in my specific aircraft?

Check with your aircraft manufacturer or kit supplier about engine compatibility. While the 916iS fits most 915iS installations, some aircraft need firewall-forward kit updates or different propeller systems to accommodate the newer engine properly.