Does Porsche use a Boxer 6 or a 180 Degree V6?

"marshknute" (marshknute) 11/05/2013 at 14:32 • Filed to: None

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While tooling about on the internet earlier, I encountered several blog threads attempting to determine whether or not Porsche in fact uses a 180 degree V6 instead of the Boxer 6 we all assumed they use. The argument always ends in an undecided stalemate. I would imagine it would be easy enough to come up with a definitive answer, but the continued internet arguments seem to indicate that that isn't the case. Anyone care to drop some nuggets of knowledge?

ShelbyRacer78-Fusion Modifier > marshknute 11/05/2013 at 14:36

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Its a boxer 6.

Brian, The Life of > marshknute 11/05/2013 at 14:37

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I just came to say the firing order on that GIF is seriously messing with my head.

Also, I do not understand the "180 V6" side of this argument. At all.

Z_Stig > ShelbyRacer78-Fusion Modifier 11/05/2013 at 14:39

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+1 though I prefer the term flat 6.

Ghost Dog - For the kittens > marshknute 11/05/2013 at 14:39

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ShelbyRacer78-Fusion Modifier > Z_Stig 11/05/2013 at 14:40

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So do I

BiTurbo228 - Dr Frankenstein of Spitfires > marshknute 11/05/2013 at 14:40

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This is a pic of a 997 crank, so from that I'd guess a true boxer engine (if I've got that right). Judging from other pics, it seems like the air-cooled ones are the same.

McMike > marshknute 11/05/2013 at 14:41

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Boxer. It resembles the top animation.

Same can be said for Subaru fours&sixes, old VW fours, Goldwing fours&sixes, BMW twins.

The only flats that were not boxers were a few Porsche eights, and all twelves.

It's all about the crankpins. the top animation has separate pins that allow the pistons that move in and out 180* opposite to each other.

Turner950s > marshknute 11/05/2013 at 14:43

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If the cylinders are 180º, directly opposing each other, it's not a V shape.

TheOnelectronic > marshknute 11/05/2013 at 14:46

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I feel like that bottom gif would vibrate like a motherfucker.

Brian, The Life of > McMike 11/05/2013 at 14:48

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OH! The GIF is supposed to represent TWO examples?

Boy do I feel dumb ...

YSI-what can brown do for you > BiTurbo228 - Dr Frankenstein of Spitfires 11/05/2013 at 14:49

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marshknute > Turner950s 11/05/2013 at 14:49

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It wouldn't be shaped like a V, but it would fire like one. The "Boxer 12" in the Ferrari BB 512 was actually a 180 degree V12, and fired like the lower part of the GIF above.

McMike > marshknute 11/05/2013 at 14:49

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Boxer engine (never mind the number of cylinders, just watch the relationship of the ones opposite from each other)

180* V engine

Tekamul > Ghost Dog - For the kittens 11/05/2013 at 14:50

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And it's just as simple as that.

McMike > Brian, The Life of 11/05/2013 at 14:51

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LOL, that's not a single four cylinder engine gif.

That's showing the difference between the two. (top is boxer, bottom is 180 V)

YSI-what can brown do for you > marshknute 11/05/2013 at 14:51

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One crankpin per cylinder = boxer
One crankpin per bank = V engine

davedave1111 > marshknute 11/05/2013 at 14:52

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It's a boxer/flat 6. Note the pairs of opposite lobes on the crankshaft.

I think a fair number of people don't realise there is a difference between a boxer and a 180-degree V6. Then again, lots of people also don't realise that the angle there refers to the timing of the two banks, not the physical angle between them, so a 180-degree v-engine doesn't necessarily have the cylinders in the same plane.

McMike > Brian, The Life of 11/05/2013 at 14:56

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I have that GIF saved to my desktop just for discussions like this.

I have never looked at it as one motor until you said something. It makes my head hurt trying to figure out the firing order on that one, too.

2-3&1—4-2-3&1—4, or

2-3—1&4-2-3—1&4,

BoxerFanatic, troublesome iconoclast. > BiTurbo228 - Dr Frankenstein of Spitfires 11/05/2013 at 15:01

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yup.

Individual crank journals per piston, 180-degrees apart for opposed pairs means that the pistons rise away from each other, and fall toward each other at the same times.

If they shared a crank journal, they would just be offset, and one would rise to TDC as the other correspondingly falls toward BDC.

The Ferrari flat-12 uses shared crankshaft journals for several reasons.

A. all v12s are inherently balanced, pretty much regardless of bank angle, just like any I6 is inherently balanced.

B. the ferrari flat 12 was directly developed from the Colombo V12 components... the crank case is just splayed out horizontally flat to minimize the height of the engine, because the engine is mounted above it's gearbox, not in front of, or behind it.

C. 12 individual connecting rod journals, plus bearing journals between them would make the crankshaft excessively long, and either the crank journals very thin, or the whole engine even longer than a 12-cylinder engine with two banks of 6 cylinders would already be. And as mentioned, the balance and vibration advantages are already inherent, and not much else to be gained.

So a Berlinetta Boxer (or it's TR->512M successors) is not really a true boxer the way a Porsche, Alfa, or Subaru, BMW motorcycle, and other horizontally opposed engines are, with opposed crankshaft journals, but i is awesome enough to let it slide anyway.

dinobot666 > marshknute 11/05/2013 at 15:04

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All I know is that it doesn't sound horrid like a V6 does, so that's the only answer I need.

McMike > TheOnelectronic 11/05/2013 at 15:09

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It would shake apart, that's why you never see it outside of 12 cylinder engines.

BoxerFanatic, troublesome iconoclast. > Turner950s 11/05/2013 at 15:09

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It has to do with whether the pistons act in unison, or 180-degrees out of phase with each other.

V engines have corresponding piston pairs sharing the same crankshaft journals. Laying that V-angle out to 180-degrees and making it 'flat', doesn't necessarily make it a true 'boxer' engine, if the pistons and their con rods still share a crankshaft journal.

A true boxer has separate journals for opposed piston pairs, so that the opposed pistons both rise toward top dead center together, and fall toward each other and bottom dead center.

They don't simultaneously shift left to right, when looking at the front aspect view of the engine. That would induce a distinct rocking/shifting motion to the whole engine, and cause vibrations in the engine, and it's mounting points to the vehicle. Rising and falling together cancels each other out, and doesn't impart that rocking motion on the engine block, and makes the engine smoother. A V engine has those rocking motions, but are offset by the angle of the block between the banks.

The Porsche cutaway animated illustration shows a true boxer engine action.

BoxerFanatic, troublesome iconoclast. > Z_Stig 11/05/2013 at 15:11

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I like the term flat 6, but a flat 6 applies to both a true boxer, and a 180-V, as both would be 'flat', so it becomes a less precise descriptor, despite sounding good.

BiTurbo228 - Dr Frankenstein of Spitfires > BoxerFanatic, troublesome iconoclast. 11/05/2013 at 15:18

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Sweet :) thanks

I wonder what other true 180 degree V engines are around. There can't be many.

BoxerFanatic, troublesome iconoclast. > BiTurbo228 - Dr Frankenstein of Spitfires 11/05/2013 at 15:39

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No, not really.

As McMike mentioned... some Porsche racing flat-eights, and flat 12s.

As each bank of the engine gets more balanced, the less advantage there is to balance across both banks.

But doing split crank pins makes crankshafts either potentially more delicate with thinner webs and journal pins, or if you keep them substantial, more journals means more length. And you have to usually keep centerline bearing journals between them, to keep the crankshaft from 'walking', moving around in it's bearings, and wearing them out sooner.

So to have a flat 8 or flat 12 that is already as long as a corresponding V8 or V12 would otherwise be... the banks are getting to be more balanced as the pistons go for a 90-degree, or a 60 degree phase interval, and even if the directly opposed piston with an opposed pair isn't directly 180-degrees out of phase, one of the other opposed pairs is 180-degrees opposed to that pair.

It becomes un-necessary to plan in the excess crankshaft length for individual opposed crankshaft journals, when there is an opposed shared crank journal, which requires at least 8 pistons in four pairs, but also applies to 12 pistons in 6 pairs.

A flat four could theoretically have a flat-crankshaft, with 2 shared crank journals, but since a two cylinder bank isn't inherently balanced itself, a 180-degree V-4 would vibrate more than a 4-journal true boxer 4, and an engine that is only ~2.5 cylinder pitch lengths long can afford to build in enough room for the journals and webs of a crank with four con-rod journals, and 5 bearing journals.

UserNotFound > marshknute 11/05/2013 at 15:59

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I vote for flat 6.

BiTurbo228 - Dr Frankenstein of Spitfires > BoxerFanatic, troublesome iconoclast. 11/05/2013 at 16:05

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Informative as ever, thanks :)

YSI-what can brown do for you > dinobot666 11/05/2013 at 16:22

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You have been listening to the wrong V6s!!

sloPro > YSI-what can brown do for you 11/05/2013 at 16:26

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in my understanding a bank is a row of cylinders. but i think i get at what you're implying so:

boxer = 1 rod journal/1 cyl separated by a main journal (thus boxer 6 = 6 rod journals + main journals), just like the original top animation.

horizontal V = 1 rod journal/2 cyl(from opposing banks) (thus 180*V12 has 6 rod journals + main journals)

also, just in general, isnt flat = boxer?

Demon-Xanth knows how to operate a street. > marshknute 11/05/2013 at 17:24

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All boxers are flat.

Not all flats are boxers.

Boxer 6:

Flat 12:

ToyDeathbot > sloPro 11/05/2013 at 17:40

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thinking the flat and boxer are the same thing is a common misconception.

the flat refers to an engine which lies flat, so that includes the Ferrari 180-degree V12 (ie. the bottom one in the gif up top). Since a boxer also lies flat, it is part of the same category.

the boxer refers specifically towards how the pistons are joined to the crankshaft, in which 2 cylinders will always oppose each other (ie. top gif).

YSI-what can brown do for you > sloPro 11/05/2013 at 20:45

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Woops, meant one per pair of cylinders. That would be one hell of an engine if the bank had the same pin.

Stef Schrader > marshknute 11/12/2013 at 00:12

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Flat six...indabutt.

PabloPistoffo > Ghost Dog - For the kittens 12/10/2015 at 12:59

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Also, Veesixter would be a stupid name for a car.