Subaru's new diesel is a horizontally opposed flat four. Aint it? It only has one crankshaft don't it?
The pistons don't punch each other do they so how are they boxing?
I am missing something aren't I?
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Yes it is, and AFAIK the configuration is so named because the pistons 'punch' in pairs like the oscillating arms of a human pugilist (you don't punch with both fists at one do you?).
And yes, there's one crank, which can of course be shorter than a straight four as it doesn't have to accommodate four bore widths side by side, which helps to make the whole engine shorter, as well as more compact vertically allowing a lower centre of gravity.
I want one ;-)
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There are two layouts for flat engines.
One, where the big ends of opposing cylinders run on the same crankpin - so, for a 4 cylinder engine, you might have 3 main bearings and 2 crankpins. This can be called a flat vee engine, and is not a boxer.
The other is where each big end has its own crankpin, and the crankpins for opposing cylinders are 180 degrees apart. In this configuration, the pistons reach inner dead centre together, and outer dead centre together, and this is the boxer configuration.
So, all boxer engines are flat, but not all flat engines are boxers!
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Check out this video
tinyurl.com/yrzzxk
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I'm confused!
So what are VW beetle engines?
I always thought horizontally opposed were in perfect balance (BMW, Douglas m'bike) etc.
I'm also confused by a statement by the late, great LJK, who described a Ferrari ninety degree V8 with a 'flat plane crankshaft' as having 'uneven firing sequences'. My maths says they should be every ninety degrees, which should be possible.
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Old Beetle engines are boxers.
My head won't do 90 degree V8s, especially after a bottle of Marston's Old Empire.
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Now my head won't stop doing 90 degree V8s - reasonably comprehensible description of flat plane v cross plane V8s here -
www.autozine.org/technical_school/engine/smooth4.h...m
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Taking a simpler example, the Citroen 2CV engine was a boxer twin where both cylinders fired at the same time, so you got just one power impulse every 2 revs, as on a single-cylinder engine. Presumably, for the same reason, that's why the Subaru flat 4 makes a noise like a 2-cylinder engine.
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I checked and the Subaru engine doesn't have paired firing like the 2CV did. So my guess was wrong.
If you want complexity, forget the Subaru - The Napier Deltic supercharged 2-stroke diesel engine had 18 cylinders, 3 crankshafts and 36 pistons! And the famous English Electric Deltic locomotives each had two of these engines!
www.wis.co.uk/justin/deltic-engine.html
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Whole new meaning to a common rail diesel !
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If you want complexity forget the Subaru - The Napier Deltic supercharged 2-stroke diesel engine had 18 cylinders 3 crankshafts and 36 pistons! And the famous English Electric Deltic locomotives each had two of these engines!
The deltic was not complex - it was a two stroke - said to be the only diesel British Rail could maintain.
Replaced with the 12 cylinder Valenta in the HST - and there is a story, and complexity.
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The 2CV engine was not arranged to have both cylinders firing together but both spark plugs sparking together - that's different.
As usual, Citroen pre-empted modern design by doing away with the distributor and firing the plugs together by using a double-ended coil. This means that each alternate spark for a given plug occurs at the top of the exhaust stroke and is superfluous. The downside is increased plug wear but the simplification of the electrical system makes this worthwhile.
The notion of a twin firing once "all together" would make for some very lumpy motoring.
659.
Edited by 659FBE on 02/08/2008 at 13:02
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The 2CV engine was not arranged to have both cylinders firing together but both spark plugs sparking together - that's different. As usual Citroen pre-empted modern design by doing away with the distributor and firing the plugs together by using a double-ended coil. This means that each alternate spark for a given plug occurs at the top of the exhaust stroke and is superfluous. The downside is increased plug wear but the simplification of the electrical system makes this worthwhile.
Like Harley Davidsons...
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So all boxer engines are flat but not all flat engines are boxers!
How interesting NC. I didn't know that.
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Slight aside. Is there any difference in performance, and/or ecomony between a flat/boxer engine and its in line equivalent?
Edited by Morgie on 05/08/2008 at 17:17
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NC wrote
"One, where the big ends of opposing cylinders run on the same crankpin - so, for a 4 cylinder engine, you might have 3 main bearings and 2 crankpins. This can be called a flat vee engine, and is not a boxer."
Do you have any production examples of this 4 cylinder 180degree flat vee ?
Or the other rarity - a 120 degree V6 ?
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I love the You Tube video of the diesel engine with a spark plug!
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The practical problem with a flat engine is the provision of auxiliary and camshaft drives. Two belts are generally required to drive the camshafts and the drive becomes unwieldy if you incorporate belt driven twin camshafts per bank in order to actuate 4 valve heads. There is no economy of duplication in a diesel because one of the drives has to be different in order to incorporate a fuel pump.
Although seemingly an attractive package, a flat engine does not offer any significant advantages to offset its greatly increased cost - which is why there are so few of them fitted to passenger cars.
(VW & Citroen RIP - no problems with pushrods and air cooling - clever design at the time).
659.
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>>Is there any difference in performance, and/or ecomony between a flat/boxer engine and its in line equivalent?
There's no inherent reason why there should be a difference. Engine configuration, generally, is just a packaging thing.
>>Do you have any production examples of this 4 cylinder 180degree flat vee ?
Off the top of my head, no, I don't. There are larger examples though, Ferrari made flat 12s which were not boxer engines.
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Flat engines can be a bit heavier than straight or vee ones. The crankcase can be bulky, there are two cylinder blocks and two cylinder heads that would be lighter if combined, and unless it's a pushrod engine the valve gear is likely to weigh more, all other things being equal. Also demands a long inlet tract if there's only one carb.
I owned a car that had a very cooking Alfasud 1300 single-carb unit. One of the very sweetest-revving engines I have known, but I know it was heavier than its Ford, Renault or Fiat equivalents.
Edited by Lud on 05/08/2008 at 21:22
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Ah - I had two Alfasuds in my youth. Brings back very fond memories of a rasping exhaust and a hole beneath my shoe. The Subaru boxers have neither!
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>>Do you have any production examples of this 4 cylinder 180degree flat vee ?Off the top of my head no I don't. There are larger examples though Ferrari made flat 12s which were not boxer engines.
I dont think the 4cyl Honda Goldwing is a boxer. Also perhaps some aircraft engines, Lycoming etc.
While strictly "boxer" indicates opposing pistons moving in and out together in practice it is used to define any 180 deg engine hence Ferrari 180deg 12 cyls were called boxers, Berlinetta Boxers, 365BB and 512BB though the engines were really flattened versions of the V12s of the same capacity - which I think has been said.
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Having looked under the bonnet of a 6 cylinder Subaru owned by a friend recently, I must say the combination of boxer engine and all-wheel drive does seem to make for a lot of ironmongery to cram under the bonnet. Does run smoothly, though.
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I know mine is very smooth!!
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Gold Wing is definitely horizontally-opposed, in either the original 999cc 4, or latest 1832cc six cylinder form. A snip at £17,000 plus:)
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Nortones, am I right in thinking this device costing as much as 17, or even 34, perfectly usable jalopies or one jolly decent brand-new motor is a, choke, motorised bicycle?
I regard people who want to drive 'supercars' every day as pretty mad, but that is truly ridiculous even for the automotive world.
(Obviously an exception must be made for any bikers here who like that sort of thing. No doubt there is some explanation in most cases).
Edited by Lud on 06/08/2008 at 16:53
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Lud. 17 large ones is indeed the asking price. Rather like a Rolls I suppose. If you have to ask, they usher one kerb-wards.
Cheddar. BMW HO twins are boxers in common parlance. The pistons move in opposite directions viewed from above.
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Cheddar. BMW HO twins are boxers in common parlance. The pistons move in opposite directions viewed from above.
Yes BMW twin are boxers. And a bit of research tells me that 4 cyl Goldwings may be too.
Nortones am I right in thinking this device costing as much as 17 or even 34 perfectly usable jalopies or one jolly decent brand-new motor is a choke motorised bicycle?
Lud, the current Goldwing is better described as a two wheeled car and has all of the disadvantages of a car and all of the disadvanatges of a motorcycle rolled into one!
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>>BMW twin are boxers
If they weren't, the unbalanced forces would be huge - it would shake the bike to bits, saying nothing for the effect upon the rider.
Perhaps some of the leather fetishists might like that sort of thing?
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Gold Wing is definitely horizontally-opposed >>
Yes, the point is that I dont think it in 4cyl form at least is a "boxer" in the strictest sense so is perhaps an example of a production 180deg flat V - as someone put it.
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One of the highlights of the Motor Show this year for me was at the Honda Dreamscape show where one of the stunt riders actually managed to wheelie a Gold Wing !
Admittedly he only got the front a couple of feet off the ground but it was impressive nonetheless.
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Dr. Lanchester invented a rather clever twin cylinder twin crank example in the late 1890s.
A "Google" for "design machinery Robert Norton perfectly balanced two cylinder engine" will find it in Norton's book (1st. link returned, which looks like a thoroughly good read, by the way).
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>>will find it in Norton's book
That must be a newer edition, because it's not in my old, battered, copy. Yes, the book is a good read - it presents the maths behind subjects which come up reasonably frequently on here, nameley engine balance, and wheel balance.
I suspect that for a flat twin, you'll get most of the benefit offered by Dr Lanchester's invention by using a boxer configuration, and the extra mass and space required by two contra-rotating cranks wouldn't be considered worthwhile.
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