ENGINE BALANCE: Inline 6 vs. V6 vs. VR6 vs. Flat / Boxer 6

what is up engine heads today we're hitting on all sixes as we explore the engine balance and the strengths and weaknesses of the four most popular 6 cylinder engine configurations the inline 6 the v6 the vr6 and the flat 6. but before we can talk about engine balance just a super quick little recap on primary and secondary engine balance if you already know about that then you can click this timestamp right here to skip primary secondary engine balance or if this is your first time watching this engine balance series you can continue watching or you can watch the first video which is this one in the series for a more detailed step-by-step easy to understand explanation of primary and especially secondary engine bounds [Music] a primary engine imbalance is the result of an unbalanced mass in the reciprocating assembly of your engine in other words your pistons are usually the greatest potential source of a primary engine imbalance an engine with an odd number of pistons is going to have a primary imbalance if the mass of the odd piston isn't balanced out by the other pistons secondary engine imbalances occur because the piston travels at different speeds at the top and bottom half of the stroke it does this because it has to cover a greater distance at the top half than at the bottom half of the stroke this occurs because although the piston moves in a simple up and down motion the connecting rod does not the conrod steps out from a linear path of motion and because it does this it pulls down the piston a greater distance during the top half of the stroke a greater distance means that the piston must travel faster to cover this greater distance and because of this there's a difference in speed between the top and bottom half of the stroke and because there's a difference in speed there's also a difference in inertial forces between the top and bottom half of the stroke and this difference in inertial forces is the source of secondary engine imbalances [Music] so that's it for primary and secondary balance now let's start with the inline six cylinder engine we already covered it twice so many of you know that it's a beautifully simple and beautifully balanced engine configuration it's beautifully simple because it needs only one cylinder head only one or two cams and only one exhaust manifold the only real downside of an inline six is its length and because of its length it's very hard to fit it transversely in an engine bay but other than the length it's very hard to fold the inline six cylinder engine it's beautifully balanced because first of all it has an even firing interval if we divide 720 which is number of degrees it takes a four-stroke engine to complete one combustion cycle by six which is the number of cylinders we get 120 degrees it tells us that the e96 cylinder engine fires every 120 degrees of crank rotation if we detect 220 from 180 we get minus 60 the minus tells us that we have 60 degrees of power stroke overlap so that's pretty significant power stroke overlap resulting in a very smooth engine when it comes to balance the inline six is essentially two inline threes mirroring each other as we know the inline three cylinder engine has a primary imbalance in relation to its center of gravity due to its odd number of pistons this is especially apparent every time the first or the last cylinder in the inline three fires when cylinder one fires for example the downward force of piston one creates a reaction at the opposite end of the engine and when piston one goes down it tries to yank the other end of the engine up now piston three cannot cancel this force out because when piston one is atop that center piston three is not at bottom dead center piston 3 isn't doing the opposite thing of piston one so it cannot cancel the force out which means that when it's running the inline three cylinder engine has a rocking moment back the front but the inline six cylinder engine does not have a primary imbalance there's two invite threes in front of a mirror so they cancel each other's rocking moment out and the ny6 has a perfect primary bounce the inline three cylinder has no issues with secondary balance because at any one time the three pistons are at different parts of their stroke which means that there's no problems with secondary balance the inline-six of course inherits this and it also has no issues with secondary [Music] bounds the v6 was created to fix the one problem of the inline six cylinder engine its length a v6 is a lot shorter than an inline six a v6 is almost as short as an inline three cylinder engine which means that fitting it transfers so in an engine bay is a lot easier than fitting a you know in six transverse like in an engine bay but the v6 has to pay a price for its compactness the first thing that it loses is the inherent primary balance of the inno and six cylinder engine in a v6 engine there is no mirroring of inline threes instead the two e93s are split into two banks of the v which means that there's no canceling out of the primary rocking moment of the inline three and instead each bank of the v of a v six inherits the primary imbalance of an ini3 and to fix it the v6 engine needs engineering aids and they usually come in the form of balancing shafts and or crankshaft counterweights large and heavy crankshaft counterweights and or offset weights in the crankshaft pulley for the flywheel but the v6 engine also needs engineering aids to have an even firing interval in our previous engine balance video we learned that if you split cylinders in a v configuration you need to decide on the angle between the two banks of the v in nav engine the perfect bank angle is the one that enables a naturally even firing interval and that bank angle equals the firing interval of the engine so in the case of a v engine with six cylinders such as a v6 the perfect bank angle is 120 degrees the same as the firing interval but a 120 degrees v6 is impractical it's very wide which means it's no longer compact which means that it neuters the compact nature and the whole purpose of a v6 because it becomes very hard to install a 120 degrees v6 into any sort of engine bay so instead we make a 60 degree 90 degree v6 or any other number of degrees that enable a more narrow bank angle which results in a more compact engine but there's an issue here any v6 that doesn't have 120 degrees between the banks needs offset crank pins to have an even firing intervals the crank pins in a v6 crankshaft are offset by what's called a spray angle display angle makes up for whatever is missing in the bank angle and although it does complicate the crankshaft it enables an even firing interval with the wrong bank angle so as you can see if it wants to be smooth like in inline 6 the v6 needs several engineering aids but it also needs double number of cylinder hits double the number of cabs if it isn't a pushrod v6 and double the number of exhaust manifolds compared to an inline 6 cylinder engine so as you can see the v6 achieves compactness and smoothness by sacrificing simplicity [Music] but what if you wanted the inherent balance and the simplicity of an inner line 6 with the compactness of the v6 but without the double cylinder heads how would you do that of course you would breed the inline-six together with the v6 and the offspring would be called vr6 in fact the vr actually means in german faux motor or translated it means v inline engine and this is exactly what the vr engine is it inherits the genes of both of its parents and its goal is to be as inherently balanced as an n96 while not being as complicated as a v6 this was the guiding principle according to which volkswagen designed the vr6 engine they wanted something that had six cylinders that they could stuff into an engine bay of a compact car but without the double cylinder heads double cams and double exhaust manifolds off a v6 engine the vr6 engine is essentially a v6 engine but it has an extremely narrow angle between the two banks of the v in the case of volkswagen engines that's either 10.6 or 15 degrees between the two banks and this very narrow angle brings the cylinders so close together that you can cover them all with a single pretty wide but still a single cylinder head when it comes to primary and secondary bounds the vr6 is almost the same as an inline six the keyword here is almost now in the vr6 we have the same firing order as in a typical inline six we even have an extremely similar crankshaft the anatomy is almost the same with the crankshaft and the vr6 of course being shorter and because we have almost the same crankshaft it means that we have the same pistons moving in the same pairs in the vr6 and in the inline six cylinder engine the difference is that narrow little degree of separation between the two banks of the vr6 which means that in the vr6 the cylinders aren't quite all in a single line which means that in the vr6 we do not have true cancelling out of two inline threes as we do in the inno six cylinder engine that being said that little angle is very narrow which means that the vr6 is still inherently a pretty smooth engine and it is better balanced than any generic v6 engine this means that unlike the v6 the vr6 needs minimal engineering aids you need some slanted pistons so you could fit a single cylinder head on two banks of separated cylinders and you need a bit of additional crankshaft counterweights to get rid of the imbalances created by the narrow angle of separation between the two cylinder banks so this means that the vr6 is the holy grail of six cylinder engine configurations it's as simple as an n96 but it's more compact than in one six well actually no it's not as simple as an inline six it's not as simple because we're fitting a single cylinder head to a bunch of cylinders that are not in a straight line this means that the combustion chambers in that cylinder head are also not going to be in a line this means that we're going to have a difference in the length between different intake and exhaust ports and this of course is not a good thing it means that different cylinders are going to have different uh power and torque curves different power bands and this of course results in a horrible engine so this inherent problem of the vr6 must be fixed with engineering aids and they come in the form of the intake and exhaust manifolds making up for the differences in length between the intake and exhaust ports and we also sometimes have different camshaft profiles employed for different cylinders to equalize their performance this of course adds a bit of mumbo jumbo and complexity to the vr6 all that being said from an engineering perspective the vr6 engine is a success it achieves its goals it's very compact it's in fact more compact than most v6 engines it's so compact that many compare it to the inline-four in terms of compactness and although it's not as simple as an inline six cylinder engine it is certainly more simple than a v6 because it has a single cylinder head the same number of cams in the 96 and the same number of intake and exhaust manifolds as an n96 and although it's not quite as inherently well balanced as an inline six it is still inherently better balanced than a v6 engine and although it does have its quirks as i said from an engineering perspective it's definitely a success our final engine configuration for today is the flat 6 or more precisely the boxer 6 engine every engine that has horizontally opposed cylinder banks is a flat engine but in order for it to be a boxer as well it must have the pistons move in and out together as you can see on this little animation for example the engine in the ferrari testarossa is a flat 12 but it's not a boxer because the connecting rods in that engine share a crank pin its pistons do not move in and out together hence it's only a flat 12 but not a boxer 12. however all the flat 6 engines we care about like the ones made by porsche or subaru are in fact boxer sixes now a boxer six just like an e96 has a mirroring or canceling out of two inline threes it's just that the boxer six does it differently in the inline six we have two annoying threes uh in a line but in the box 36 we have them horizontally opposed so they can cancel each other out but there's a little catch with the boxer engine in order for the pistons to move in and out together they must each have their own crank pin which means that the pistons in a boxer engine are not truly directly horizontally opposed to have them truly directly horizontally opposing each other we would need a very complicated connecting rod arrangement which of course wouldn't be practical for manufacturing purposes and this offset between the pistons of a boxer engine means that the two inline threes in a boxer six are also offset from each other which means that they're not cancelling each other fully but what's important is the size of the offset in relation to the size of the engine for example in the boxer twin engine which is only two cylinders the size of the offset is almost half the engine which means that it creates significant imbalances for example bmw motorcycles have these engines in them and you will see that more modern versions of the bmw boxer twin actually use balancing shafts to get rid of these imbalances but in the boxer 6 the size of the offset is extremely small in relation to the total engine size which means that the imbalances created by this little offset in the boxer 6 are pretty much irrelevant so the boxer 6 is pretty much perfectly balanced because it too does a lot of the canceling out of the inline threes but it has another ace up its sleeve it has a very short and a very light crankshaft and it can have a very wide crankshaft because its crankshaft has very small narrow and light counterweights and can afford to do this because of its horizontally opposed layout as you might know in an inline engine configuration the crankshaft counterweight cannot be used to balance out the mass of the piston and the conrod it cannot do this because while the crankshaft counterweight rotates the piston reciprocates this means that when they're in this position the counterweight can indeed cancel out the mass of the piston but as the engine rotates further we can see that the counterweight now points in a totally different direction to the piston which means that it cannot cancel out the mass of a piston which means that crankshaft counterweights in inline engines actually only cancel out the mass of the crank pin and the part of the rod that is right onto the crankbait so this is why inline six cylinder engines and other inline engines for example need relatively heavy counterweights to crank to cancel out the mass of the crank pins but the fire six engine doesn't need this because it's a boxer 6 engine we have the crank pins opposed from each other horizontally at 180 degrees which means that the crank pins in the flat 6 can actually cancel each other out for the most part which means that in theory you can actually make the crankshaft of a boxer 6 engine without any counterweights actually porsche did that in the past but as you can as you can see modern fire 6 engines actually all of them have crankshaft counterweights here's one from porsche here's the easy 30 from subaru for example they all have counterweights now they have count rates because counterweights in a crankshaft do a great deal in improving the longevity of the engine they reduce the dynamic stresses and the fatigue of the engine and they also reduce the loads on the main bearings now how exactly all that works is a topic for another video which i may cover in the future so being able to have very small counterweights reduces crankshaft mass which means that the flat 6 can be a very very rev happy engine since we're speaking about crankshafts we also must mention crankshaft length and torsional vibration this is something where the inline six seems a bit of a loser because it does have the longest crankshaft which means that it is susceptible to the most torsional vibration torsional vibration occurs when you apply torsion actually when you apply a load to a shaft at a length at a distance from some sort of resistive mold in our case the shaft is of course our crankshaft our load is of course the piston under combustion and our resistive hole is of course the clutch for example the longer the shaft the greater the torsional vibration this means that the inline six engine which is the longest and has the longest crankshaft is subject to the most torsional vibration now you can't really feel torsional vibration outside the engine but it can actually destroy an engine and a crankshaft however in our previous video where we covered the inline six we have learned that the right engineering the right material at the right places can definitely pretty much eliminate torsional vibration issues from modern innovation 6 engines which are capable of sustaining extremely high loads even in the most modified of their versions that being said eliminating torsional vibration concerns usually means adding material adding strength and thus adding mass which means that when it comes to crankshaft design the flat six is a winner so overall the flat 6 is a winner well yes it is very balanced yes it does have a very light crankshaft but there is of course a price to be paid and the flat 6 pays the price in being the most complex engine configuration of all the four engine configurations we talked about today it's also horrible for packaging because it's very wide and stuffing it into an engine bay is definitely not easy when it comes to the complexity we mentioned it it does have two cylinder heads two exhaust manifolds complicated intake manifolds usually uh it also has pretty complicated timing build or timing chain arrangements even the engine block has to be made of two halves so it's definitely the most expensive and complex engine to manufacture which explains why although it is very awesome it is a very rare engine configuration so that's it when it comes to the most popular six cylinder engine configurations i hope you enjoyed that found it useful and maybe even a bit entertaining in the future we will of course explore more engine configurations uh in the engine balancing series we will also talk about flat plane and cross point stuff and much much more so if you're enjoying this stay tuned for that as well as always thanks a lot for watching and i'll be seeing you soon with more fun and useful stuff on the default channel

Channel: driving 4 answers

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Keywords: inline six, flat six, boxer six, engineering explained, how it works, vw, vr6, volkswagen, porsche flat six, porsche boxer six, porsche mezger engine, porsche 911 flat six engine, vw vr6, inline 6, boxer 6, boxer 6 engine, inline six vs v6, v6 vs vr6, engine balance, 2jz, ford barra, bmw s54, rb26, inline 6 vs v6, subaru flat six, subaru ez30, subaru ez36, subaru flat 6, flat engine vs boxer, flat engine vs v engine, d4a, driving 4 answers

Id: mTS48jX68YU

Length: 19min 48sec (1188 seconds)

Published: Sun Mar 14 2021