26

I know that boxer engines are those which have pistons moving in the opposite direction.

Also the fact that since they sit low, the center of gravity is lower which causes better handling.

  1. Why don't mainstream manufacturers use the Boxer configuration (sans Subaru and the BR-Z cars; also not including the VW Beetle and the Tata Nano)?
  2. What are the disadvantages?
  • If you want to see the disadvantages just try changing a head gasket (or rather 2 head gaskets). Or even just changing the spark plugs... ;-) – R.. Feb 12 '16 at 15:18
  • Porsche use them also, It works for them as they sit low for the mid/rear engine configurations – JBB Feb 12 '16 at 15:45
  • @R.. spark plugs on Subaru engines aren't that bad, I agree on the heads though. And eventually on higher mileage Subaru engines the head gaskets form an external leak, Not to mention constant failure of the spark plug tube seals. – Ben Feb 13 '16 at 4:57
  • I think vini's answer is pretty clear from experience. – Ppoggio Mar 4 '16 at 5:30
  • @R.. like taking the front wheels off a Jowett Javelin to change its spark plugs? (Though Dad tells me you can just get them with the steering at full lock) – Brian Drummond Nov 19 '16 at 20:02
14

Like V configuration piston engines , boxer or flat configuration engines can be made approximately half the length of a straight configuration engines. Compared to V engines boxers are not as tall, offering the ability to position mass lower in the vehicle's chassis, but are wider.

All boxer engines feature low primary vibration as pairs of pistons are opposed and move in a way to cancel out each other's momentum.

Like Vs boxers are more complex that straight engines, having 2 cylinder heads with associated head gaskets, exhaust manifolds etc., and double the number of camshafts, more complex camshaft chains or belts and more complex cooling.

Compared to Vs, boxer engines have a more complex crankshaft as they have a crank throw for each connecting rod. True V's have pairs of rods sharing each crank throw.

The probable reason boxer or flat configurations are not used very often in modern cars is because a straight or V engines are almost always a better choice.

Many cars are now front wheel drive which work best with a compact, transversely mounted engine. A straight-4 or a V6 are much more suitable that a flat-4 or flat-6 in this configuration.

Longitudinal mounted engines are preferred for front-engine, rear wheel drive, the boxer engine's lower mass probably does not provide enough advantage over the simpler straight-4 or V6.

Where boxer's really do seem to work is in air-cooled rear-engined cars (e.g., the VW Type-1 and Porsche 911) where width is less of a concern, the engine must be a short as possible to avoid a large mass behind the rear axle, and the banks of cylinders are easier to cool as they are more widely spaced from each other.

With regards to the modern Subaru layout, which originally featured 4-cylinder engines and all wheel drive, a longitudinal mounted boxer makes sense. To accommodate front wheel drive-shafts the engine must be placed in front of the front axle line, and the short, low boxer engine has advantages. (Compare this with the original all wheel drive Audi 80 Quatro that had a straight-5 hanging way-out ahead of the front axle.)

At one point flat-12 engines were used in racing cars such as the Porsche 917, and many Ferrari F-1 cars (although these were technically 180° V-12s, which may have any cylinder bank angle). Flat-12's proved incompatible with ground-effects as the cylinder heads occupied the space where the venturi tunnels needed to be.

19

Boxer engines are large and complex that is their greatest fault.

The engines have a larger widths when compared to an inline 4 or a V6. If you have ever replaced spark plugs on a Subaru those engines are shoehorned in very tight. Not all manufacturers want to work around that kind of width.

The engines are also more complex. The cylinder block is split into two halves. This requires the manufacture of two complex items instead of just one.

Finally the needed orientation of the engine provides extra problems. These engines are oriented in a traditional manner. Because the transmission sticks out the back the power flow has to turn 180 degrees to go to the front wheels. Since most vehicles are front wheel drive this makes the transmission more complex.

The advantage of a boxer engine is that the engine counter balances itself. The pistons that are across from each other move toward the crank and away from the crank at the same time. This gives smoother operation and a crank shaft that is lighter because no counter balance weights are required. It also reduces vibration.

Another advantage is that because the engine is wide and short it lowers the vehicles center of gravity. This reduces body roll and improves handling.

As far as a complex transmission in concerned, Subaru uses it's complexity to its advantage by the addition of AWD.

  • 3
    So, are there any advantages? Why does Subaru stick to it? Tradition? – I have no idea what I'm doing Feb 12 '16 at 13:00
  • @IhavenoideawhatI'mdoing: it's a key part of their AWD design, and the low center of gravity is probably nice for the handling/feel of the vehicle. – R.. Feb 12 '16 at 15:17
  • 1
    I have changed the spark plugs on my Subaru, but I drive it more than I spend doing maintenance, so the advantages of a low, smooth, powerful engine are considerable. AWD helps (I was skeptical at first) with cornering and other situations, it is really nice. The engine design is similar to the Piper Cub engine, right? If it was good enough for an airplane... I was wondering though how the oil reaches the crankshaft. I thought that in a conventional engine the crankshaft sits in the pool of oil in the pan? – user15009 Feb 12 '16 at 20:25
  • @nocomprende All car engines use a full pressure lubrication system. A pump pulls oil from the oil plan and pushes it through the oil filter and then through oil gallies to all the rotating parts of the engine. Then oil then squirts past the bearings and returns to the pan through oil return passages. Only very small engines use splash lube. Submerging the crank shaft in oil robs a lot of power from the engine. For this reason the crankshaft in a car is well above the oil pan. – vini_i Feb 12 '16 at 22:21
  • In my experience working on Subarus, they generally don't mount the engines low enough to take advantage of the center of gravity, for the most part, the center of gravity in their road cars is similar to that of a V6. I haven't workd on one, but from what I've read, the Toyota/Subaru 86/FRS/BR-Z is the first of their brand to be designed around taking advantage of the low engine mounting point. – MooseLucifer Feb 16 '16 at 15:40
2

I have a '15 forester with the 2.5/6m configuration.

Replacing the spark plugs is expensive but that is about it for any disadvantages. Oh, and it's a bit underpowered.

The flatness of the motor allows for a very low hood - which provides for a large windshield. Forward visibility is awesome. It also lowers the vehicle's center of gravity, making for excellent snow/rain cornering.

The flat engine primarily allows Subaru to utilize equal length drive shafts for both front wheels, resulting in quick AWD actuation for the price - notice I said "for the price."

  • Interesting points on equal length driveshafts.. – Shobin P Apr 25 '18 at 6:39
1

Boxer engines do have their place and are especially suitable for conditions where high continuous torque is required and continuous cooling is offered. The newest cars with CVT transmissions are a great match for boxers, but currently aren't offered, because of transverse arrangement....but it's only a matter of time. Some of the most legendary race cars like the Porsche 917 used a boxer. Many legendary Cessna and Piper aircraft still employ boxers as their powerplant of choice. The Napier-Sabre 24 cylinder double boxer engine used by Hawker Typhoon & Tempest produced an astonishing 3,500 HP. Drivers who like to punch accelerator pedals and shift gears won't find boxers appealing and will remain confined to needing a computer to manage inline or V-engines and transmissions for them. Boxers are also a good match for hybrid cars where a constant-rev power plant recharges batteries to extend the cars range. Inlines and V-engines are for different conditions that compensate for traditionally abusive operating conditions.

Not the answer you're looking for? Browse other questions tagged or ask your own question.