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NOV 11, 2026 · 6 min read

What is a boxer engine? Why Subaru and Porsche lay their pistons flat

Cutaway of the Subaru Crosstrek hybrid's 2.5-liter boxer engine, showing the horizontally opposed cylinders
Photo: TTTNIS

Every Subaru with a gas engine uses a boxer, and so did the very first Porsche 911. Lay the cylinders flat, set them against each other, and you get an engine that sits low and runs smooth.

The short answer

A boxer engine is a flat engine: its cylinders sit horizontally on opposite sides of the crankshaft, and each opposing pair of pistons moves in and out at the same time, like two boxers trading punches. That cancels much of the vibration and lets the engine sit low, which lowers the car's center of gravity. The trade is width, cost and more parts to service.

How does a boxer engine work?

The cylinders lie flat in two banks, and the pistons sit on opposite sides of the crankshaft, half pointing left and half pointing right.

Subaru describes the pistons moving horizontally in a "punch-counterpunch rhythm". When one piston travels out, its partner on the other side travels out too, then both come back in. Porsche's Boxster even takes its name from the layout: Porsche says the word merges "Boxer" with roadster.

Is every flat engine a boxer?

No. Jalopnik draws the line at the crankshaft. In a true boxer, every piston gets its own crankpin, so opposing pistons can move in and out together. In a flat engine that isn't a boxer, the pistons are paired up on shared crankpins.

That's why Ferrari's Berlinetta Boxer, despite the name, has a horizontally opposed engine that Jalopnik says isn't a boxer.

Why use a boxer engine?

It sits low. With the cylinders lying flat, the engine is short top to bottom and can be mounted low in the chassis. Subaru, Porsche and Toyota all say a low engine lowers the center of gravity, which Subaru links to stability, responsiveness and grip.

It runs smooth. Because each pair of pistons moves in opposite directions, their forces largely cancel. Subaru says the opposing pistons cancel each other's inertia, and Porsche calls its flat engine particularly smooth, with no free moments or free forces.

It isn't perfect in four-cylinder form. SlashGear notes that a boxer-four tends to rock front to back, because its cylinder pairs are offset. In a six-cylinder boxer, it says, all those forces and rocking cancel out.

Subaru adds a safety claim: the engine is designed to drop below the cabin in a frontal crash, which it says helps protect the people inside.

What are the downsides?

More parts. A boxer needs two cylinder heads where an inline engine needs one, and SlashGear says an inline twin-cam engine has half as many heads, camshafts and timing chains. Porsche agrees a flat engine takes more effort to build than an inline one for that reason.

Cost and service. SlashGear calls the boxer more costly to produce and harder to service. Capital One says routine jobs like spark plugs take mechanics longer, and even Subaru South Africa admits a plug change can feel like an arduous task.

Width. A wide engine crowds the engine bay. SlashGear says it shapes decisions on suspension geometry and steering angle.

Which cars have a boxer engine?

From the makers' own pages:

CarEnginePower
Subaru Crosstrek2.5-liter boxer180 hp, 178 lb-ft
Subaru Forester, Outback2.5-liter boxer180 hp
Subaru Outback (turbo)2.4-liter turbo boxer260 hp, 277 lb-ft
Subaru BRZ2.4-liter boxer-four (FA24)228 hp, 184 lb-ft
Toyota GR862.4-liter boxer-four (FA-24)228 hp, 184 lb-ft
Porsche 911 Carrera3.0-liter twin-turbo boxer394 PS
Porsche 911 Carrera GTS (T-Hybrid)3.6-liter boxer485 PS (engine alone)

Subaru says every one of its vehicles with a combustion engine uses its boxer. Toyota's GR86 and Subaru's BRZ were developed together, and both use the same 2.4-liter engine (Subaru writes FA24, Toyota FA-24).

Where did the boxer come from?

Mercedes-Benz traces it to Carl Benz's "contra engine", with the cylinders set opposite each other, which it calls the birth of the horizontally opposed engine. Porsche dates that invention to 1896.

Volkswagen's Beetle ran an air-cooled boxer-four in the rear, and Porsche says its own flat engines trace back to it: the first Porsche, the 356 "No. 1" Roadster, used a tuned VW flat-four. The 911 arrived in 1963 as the type 901, with a six-cylinder boxer making 130 PS. Subaru built its first boxer for the Subaru 1000 in 1966, and BMW's first motorcycle, the R 32, used one too.

On the street

Subaru puts the name right in its spec sheets: the BRZ's engine is listed as the FA24, horizontally opposed, a SUBARU BOXER. Porsche's press pages call the 911's engine a boxer too.

If you're shopping, the width is the thing to know. Access to parts on either side of the engine can be tighter, so routine jobs like spark plugs can take a mechanic longer.

FAQ

Why is it called a boxer engine?

Because each opposing pair of pistons moves in and out together, like a pair of boxing gloves. Subaru South Africa compares it to two boxers throwing punches at each other.

Is the Porsche 911 a boxer engine?

Yes. Porsche says the first 911 used an air-cooled six-cylinder boxer, and today's 911 Carrera uses a twin-turbo 3.0-liter boxer.

How many boxer engines has Subaru built?

In its 50th-anniversary release, Subaru said it had built more than 16 million in 50 years.

Sources