What Are The Real Advantages Of Boxer (FLAT) Engines?

Well I've been wondering now for awhile what exactly are the advantages of the flat engine design? I know that Porsche has used them since the start and Subaru has been using them for many many years.

About the only advantage I can see is that it would lower the center of gravity on the car making it handle better.

But aparantly there are some other advanteges to this design. I've heard from some folks that boxer engines have a broader torque curve, some say they lastlonger.

What's the deal? Anyone know?

Later,
Dustin

1969 Porsche 912
1972 OPEL GT
1987 Shelby CSX #290
1992 Nissan 300ZX

and Soon a 1997 Subaru Legacy GT to thake the place of my beloved but worn out 300ZX.

I think you could throw engine primary balance in there, with the opposed cylinders. It would also seem for an air cooled engine that couldn't sit out in the breeze this lay out would facilitate the mechanical cooling.

Anymore Opinions?

Perhaps this is what was said above, but the inertial forces counteract one another nicely in these engines. Better balanced that is.

If they're good enough for airplanes.....

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'83 SC

Cooling. Take off all the shrouds and mount the motor on the front of an airplane with a prop on the crank. Makes you think of the P motor in a whole different light doesn't it.

Space savers. They are also lightweight in design. But most of all they just look cool.

Don't dismiss a low centre of gravity - its the essence of good handling - Ever noticed how many roll-over fatalities occur in SUVs?

The Porsche engine is NOT a true boxer. In a true boxer engine the opposing cylinders are on the same cycle and (in theory) cancel out each others lateral force.

The Porsche engine is in fact a V6, but with a 180 degree V. Because of 4 stroke, 6 cylinder equation, 6 cylinder engines are inherantly balanced, leading to a nice smooth feel and (more importantly) very high revving ability free from significant vibration.

The major drawbacks of the flat 6 design include obvious stuff like cost, and width. Less obvious are problems with the centrifugal forces of cornering - oil tends to get thrown into the cylinders and pistons on the outside of a corner, and the inner side of the engine is starved of oil. Porsche get around this by good design of the residual "sump" and the dry sump lubrication system that ensures the bulk of the oil is in a separate tank or circulating around the engine/oil radiator at any given time.

There is obviously a whole lot more to say on this topic, but rest assured, the 911 engine is one of the 20th century's finest...

- roGER

You're right, the P-motor is not a true boxer but an F6 (F=flat). Interesting design, and it has lasted all these years.

I read someplace that the original engine for the VW was based on an aircooled aircraft engine DR Porsche designed in 1912. Simplicity, weight to power ratio and balance were the main factors. The little "four" has become our big sixes and even the 12 cylinder monster motors that powered the 917s years ago.

Yea, the "original" P-engine was of radial aircraft design. The company Dr. Porsche was working with canned it. He split and did his own thing. Good for us!

What do you mean "not a true boxer engine", does that mean that the cylinders aren't exactly opposite from each other? If so, then neither are other flat 4 subaru, and air cooled vw engines, in fact, I doubt there's ANY engine that's a "true" boxer, I don't see how that would be possible, since the crankshaft can't handle two con-rods at the same spot.

Can anybody explain further?

69-912, very interesting cars, Opel GT is a car I have a sweet spot for, not to dis the others. If you're reading this, is the 300zx a twin turbo? If so, how reliable has it been? BTW, Subarus seem to do real good at the auto-xes. Nice cars no less...
Ahmet

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It's all the driver...

Our P-motors aren't true boxers? How about them Ferrari "boxer" 12s?

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Jeff
1976 911S

The horizontally opposed configuration for aircraft engines became popular because they offered a low frontal area and therefore could be contained in a smaller, more streamlined shape. This also had the advantage of better visibility for the pilot when the engine was mounted up front.

I think everyone else in this thread has touched upon the advantages of such an engine in a car; low positioned c of g, nice even cooling, etc.

As for the VW engine, that was designed by a guy named Francis Xavier Reimspiess (who also designed the VW emblem), under the direction of Ferdinand Porsche. I believe that Ferdinand always wanted to put a two-stroke engine in what became the Beetle, but World War Two intervened, and after the war the French put Ferdinand in jail, etc, etc (it's a long story).

If you research all of the different engine configurations that Ferdinand considered, you really start to see what a genius the guy was. One had a great big armature on it that was used as a starter/generator (more airplane technology used to this day). The armature was also the engine's flywheel. Then there's my favourite, a four cylinder where the first two cylinders were supercharged by the next two.

You asked an excellent question, 69-912. The next time any of you guys go out in the garage and open the decklid, take a moment to reflect on the incredible machines that the brilliant minds of three generations of family Porsche have provided us with.

I have to stop now. I'm getting all misty eyed.

1.2 Gees wanted to know why its not strictly speaking a boxer engine:

If the 911 was a true boxer engine, the timing and hence firing order would be different, since each pair of cylinders would be on the same stroke...

Its kind of hard to explain without a diagram...

But if you look at the firing order of your 911 engine, then it starts with 1, followed 6, and while No: 1 is firing, No: 6 is on the compression stroke...

The Ferrari Boxer is no more a boxer than a 911 - its a V12 with a 180 degree "V."

- roGER

How about the Subaru H4s? Would they be considerd Boxers or just flat 4s?

[M.D. Holloway]

I had to bring this back...great info!!!

[jurhip]

I believe a true boxer engine has all cylinders hitting TDC at the same time. Firing order doesn't matter (i.e. one can be on a compression stroke and another on exhaust). Someone feel free to correct me though.

In practice, the flat engine design offers very little advantages compared to others out there. They all have advantages and disadvantages that can be overcome to the same effect with design, materials, etc. As others have mentioned Porsche uses this design because that was what Mr. Porsche was used to. It has since become a legacy for them (it also suit aircooling - great for an aircraft since air is "free" and a reliable coolant source. you don't want to be at 15k ft and loose a water pump)

Porsche has proven very good at ensuring materials, manufacturing and design ensures a great engine. But, that doesn't make the basic engine layout great. Personally, I view the american v-8 as one of the best engines out there. For its displacement, it is extremely compact. It can produce tons of power in a reliable fashion and is extremely simple. Hi-Tech is cool, but there is genius in simplicity.

[M.D. Holloway]

Great point!

[psalt]

I had to bring this back...great info!!!


But it is incorrect, firing order is not relevent.

The 911 has a boxer engine largely because Hitler was driven on campaign thousand of miles in a Tatra T11. This 1921 Hans Ledwinka design had an force fan, air cooled, boxer engine with a backbone chassis and independent suspension. Hitler dictated these design specs to Porsche. Porsche knew he was stealing Ledwinka's work because he inherited Ledwinka's desk at Steyr and testified that Hitler assured him that Hitler would take care of the patent issues. VW settled out of court after Ledwinka died.

[patssle]

Is there a bigger animation of that 911 engine?