What are the advantages of a "boxer" engine, as used in Suburu and Porsche?

Dear Car Talk

Dear Car Talk | Apr 01, 2002

Dear Tom and Ray:

I have a question about horizontally opposed, or "boxer," engines. To the best of my knowledge, only Porsche and Subaru use this type of engine design now. Subaru goes so far as to point out the advantages of this design in its literature. Assuming that these advantages are real, why don't the other car makers use this design? Since this design is not new, I can't believe that Porsche and Subaru have found something that the others haven't caught on to yet. What's the real story? -- Jim

TOM: Great question, Jim. The boxer engine, also called a "flat engine" or "pancake engine," is an engine whose cylinders are laid down on their sides. So instead of pumping up and down, as on an "in line" engine, or diagonally, as on a "V" engine, the pistons are "horizontally opposed," or on opposite sides of the crankshaft, pumping toward one another.

RAY: The major advantage of a flat engine is that it's flatter, which means it can be installed closer to the ground. And with the mass of the engine lower, the car's center of gravity is lower. And the lower a car's center of gravity, the better the car's handling.

TOM: The engine is the single largest mass in the car (unless my brother is behind the wheel). And in fact, sources tell us that one of the problems with the previous generation of Ford Explorers (which, you might remember, had some handling issues) is that Ford made a series of engineering compromises that resulted in the engine being a few inches higher than it should ideally be.

RAY: So in addition to making the new Explorer longer and wider, the center of gravity was also lowered. And lowering the center of gravity by even a fraction of an inch can result in handling improvements that a driver will notice.

TOM: So why doesn't everybody use a flat engine? Well, I think there are two reasons. One is packaging. A flat engine is a wide engine, for obvious reasons. And a lot of designers don't want to design wide engine compartments. A "V" engine, on the other hand, is the closest to a square in shape, and it tends to fit engine compartments more easily.

RAY: The other reason why you don't see more flat engines is because of tradition. Manufacturers tend to do things the way they've always done them. Plus, they have a lot of money and engineering time invested in their current engines and are reluctant to start over.

TOM: Interestingly, however, GM now owns part of Subaru and is planning some new GM vehicles that use Subaru platforms. So it'll be interesting to see whether flat engines start to make a comeback. If you see the introduction of the new Pontiac Pancake, Jim, you'll know what's happening.

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