Like a two cylinder boxer engine but instead of having the pistons going out at the same time, and in at the same time, (piston rods attached to its own crank separated by 180 degrees) the two cylinder
180 degree V2 has the pistons going left at the same time, and right at the same time (piston rods attached to the same crank).
The Harley Davidson V2 is the same but with the cylinders at a weird angle.
Any four stroke V2 engine will have a weird fireing order, like
cyl 1 fire exhaust suck compress cyl 2 compress fire exhaust suck
This is why the HD V2 is so rough and uneven at idle. There are plenty of MC drivers that, for some weird reason, likes vibrating engines and this creates a market for the large displacement V2 engines. However, I don't know if anyone actually makes a flat V2. Perhaps it shakes too much even for a Harley rider.
Sorry, perhaps I'm missing something on this tread by coming in late.
Actually - BMW built them for years, both Porsche and VW swiped the basic timing and layout for their own engines, the Russians I think still build them as a cycle motor and they are the stock and trade of most Onan Generators. Several aircraft engines use a an opposed twin as well.
Not to appear unfriendly or anything - but they are perhaps the most smooth operational twin cylinder design I can think of off hand actually. The only trick to them is that the moving components have to be in practically perfect balance or then, as you comment, they start to beat themselves to death almost immediately.
As to Harley's - well - it's a lifestyle statement at the end of I day I fear.
But what the heck - whatever floats your boat I say..
Ah, but that's a boxer - both pistons are at TDC at the same time. Apparently a V-2 or flat V-2 has one at TDC, one at BDC. Lots of mass moving in the wrong directions there.
Synchroninzing those Bing carbs is an absolute bitch, at least on the '77 R100/7 that I had. Nice bike, but MAN, those carbs...
Oh, I see. It was just an opinion was it? You really should state your opinions less categorically if you're going to pull others up for it. I stand by my "statement of a specific measurable physical phenomenon" even though I haven't measured it, am never likely to measure it, and have never implied that I did. I presume you haven't either? Yet you continue to argue vehemently that the reverse is true. So we're both as bad as each-other.
The proportion is not constant. That is the point which you seem to be missing here. The moving-mass forces have a fixed waveform for a fixed RPM. That allows simple timing-chain driven balance shafts to go some way towards canceling them out. The combustion forces vary wildly and independently of RPM. Perhaps you can explain how you think the balance shafts, whilst rotating at a constant RPM, might be able to cancel out forces which can vary by an order of magnitude or so at the twitch of the right foot.
If they were calibrated for full power (assuming it's even possible) they would be hideously out of balance on overrun, or even just off the cam. I dread to think what would happen at idle with a simulated minus god-knows-how-many BHPs worth of vibration going on!
Only because you've jumped to the conclusion that I think the extra vibration of a straight 4 is a "problem". It's there alright but, no, I don't find it a problem at 200ish BHP. Maybe at 250BHP I might. Others might get annoyed by it even at 150BHP - who knows?
From my point of view, this is a theoretical discussion of how much vibration a straight 4 produces compared to a V6. That appears to be the only difference of opinion we have. I think the four will vibrate more, you seem to be saying that's not the case. I'm sure you'll correct me if wrong on that.
Yep. Exactly the same issues are there going from 4 to 6. Just in smaller quantities.
I'll take your word, at least as far as straight sixes having some advantage over V6s is concerned. I've never disputed that the moving-mass forces exist in a V6, and are awkward. All I did was point out the (IMHO much larger) combustion forces that also exist in both engines, but which are worse in a four than a six.
If there was an engine mount that could remove *all* the vibration across *all* frequencies, then it would make the whole argument academic (which it pretty-much is anyway). Such a beast doesn't exist.
If 4WD is the only way I can get some power to the back wheels, then
4WD it will have to be. I'm not thinking of buying one but If I do, I promise to cover all the badges up with gaffer tape.
Yep. you're getting nowhere alright ;o)
I'm totally baffled by this engine mount thing. Are you saying that the engine mounts might somehow absorb more vibration from a four than a six? How does an engine mount know how many cylinders there are? If you're saying that the engine mounts might be tuned to the particular frequencies that a four might produce, then that can equally be done for a six, canceling out any possible effects.
See above for balance shafts.
"My mind is made up. Stop trying to blind me with the facts!"
AHHH - that's what the commentary was about. Thanks.
A popular mode was to fit a narrow balance tube between the manifolds around here. Don't know that it helped much though. I don't know - I went with a series of Kawasaki solutions after my one and only BSA tried to kill me repeatedly the only summer I owned it. Traded it for a carton of Dunhills and a case of bear in the fall - and still think I got the better of the deal to this day.. : ) ..
As to the offset V - I was reading Smokey Yunick's book on performance V-8's and he had some interesting observations on this. A lot of F1 engines were supposed to be 180 degree offsets. If I understand waht he wrote - basically - he was in favour of the 180 degree V sequence if you can carry a big enough crank lobe to offset the power being delivered.
On a V-Twin, I'll wager they trying increase the torque output on the engine at the cost of higher revolutions. Put in a wide enough set of pistons and a long enough set of rods and you might get a much bigger torque figure for the rated horse power. But, RPM would have to be severely limited and you would need a fairly over square bore to make the crank lobes big enough.
Pretty much any engine design can ultimately be balanced out on it's crank I now figure. However - depending on what you do, you start to eat into the safety margin pretty quickly as you increase the internal weight according to Smokey.
All that said - what the hell do I know - I can't figure out if a series of small problems on my 93 Aero are indicating a larger problem - or if they are just a series of small problems that seem to be interrelated.
Well, I ended up buying a venturi gizmo (polysynch maybe?) that also comes in handy for balancing the triple carbs on the Saab 2-stroke engines, so it worked out OK.
Right, because there are definately engineering-specific meanings to "step backwards", is that it?
Ehhh... (I'm seeing this as a friendly joust, by the way, if I'm really pissing you off that's not my intent at all). Saying that vibration (a real, mechanical thing) is greater (a quantitfication of an amount) with (a) as opposed to (b) is talking about real, measurable things.
Right. At maximum engine output, it's biggest. When the engine is at maximum output, that's almost certainly where the balance shafts are set up to provide maximum benefit. As I've said. So I haven't missed your point, I'm just asking how important it is.
Yes.
I'm not saying that, at all. The balance shafts almost certainly are set up to do the most good when the most balancing is needed. It's almost insane to have to write that. IF that's a large part of the forces, then it'll be tuned/balanced accordingly. If, however, it's mostly about reciprocating mass, then the balance shafts' effect is mostly constant regardless of output vs RPM.
IF, and only if, the combustion forces are that much more than all that spinning mass going up and down.
And yet, from empirical evidence, there isn't a problem. Therefore your assumption must be flawed.
Probably the folks who designed the engine, they might, all things considered.
You're oversimplifying. WHICH 4 more than WHICH 6? If the question is "CAN a V6 be made more smooth than a I4", maybe the answer is yes. If the question is, as I thought it was, "Is the GM V6 more smooth than the Saab I4", I think the answer is up in the air at best.
Not hardly. No symmetry at all in a 1.
At least in a 4, they're all going in the same direction. Heck of a lot easier to deal with one vector than two intersecting ones.
Never said it did. Are we talking about vibration in a car, or not?
Fine, enjoy.
Pot. Kettle. Black.
Depends on the engine mount. Depends on the four. Depends on the six. Depends on the priorities of the engineers (or, usually, their managers). If the engine and mount are from GM, I'd suspect it more than an engine and mount from Saab. For starters, the mount in the Saab was designed for that specific engine in that specific car. The GM engine mount, for all I know, is "whatever we have already with a 4" bolt spacing".
Can be. Is it?
Indeed.
Correction, then. I've seen none of the former, and much of the latter.
I think that the problem with a V6 is really that it is 2 conjoined I3 engines. Because the vibration forces are applied at different angles they cannot cancel out.
Don't worry, I'll let you know if you piss me off.
It's also possible to measure the number of people who happen to buy V6s and who know an awful lot more about the subject than you and me put together. If that number is greater than zero, then your statement was incorrect. Care to take a bet?
As I've said before, if you can somehow make the engine balanced at full power, then whatever is doing the balancing will have an equal and negative effect on overrun. That would be really easy to spot since the vibration would increase when you lift off the accelerator. My balance-shafted straight four certainly doesn't behave like that, does yours?
You seem to be forgetting that it isn't possible to turn off a balance shaft. If it's generating enough force to cancel out the combustion forces at full power (Not that that is very likely to be possible) then it will still produce the same large forces on overrun at the same RPM, with no combustion forces to balance them out. The effect would be no improvement, Just an engine that vibrates as badly on overrun as a *real* engine vibrates on full power.
And at high powers they are. Stick your right foot down and feel it for yourself.
You need to look a bit further up to your incorrect assumption about balance shafts in order to see why you're wrong here.
Yep. Or even the dreaded marketing morons.
If you're going to get to the bottom of this the you *have* to keep it simple.
There's no symmetry at-all in an I2 either, though there could be if it was made with the pistons 180 degrees out of phase. They're not made like that though, because that would compromise the combustion force problem because of uneven firing. The moving-mass forces aren't as important as the combustion forces in engine vibration terms - particularly in engines making high specific powers.
I'm sorry. When you said "If the vibration never gets anywhere", I went and assumed you wanted to consider the possibility of a perfect engine mount. Silly me.
I'm talking about engines in isolation, in order to keep the debate down to manageable proportions. I'm also talking only about one aspect of the engine - vibration. You keep trying to drag cars into it.
Indeed. The kettle was forced to make a counter-claim of blackness against the pot, in response to a pre-emptive strike.
You're absolutely right. It all becomes a completely unmanageable mess when you start trying to include engine mounts, and it could well obscure the fundamental differences between engine types that we're trying to explore. Hang on... That's what I've been saying all along!
Who knows? Who cares? Engine mounts are irrelevant to whether one engine vibrates more than another.
... which you dismissed out of hand again. It doesn't matter how much you try to ignore it - it isn't gong to go away.
I've never denied that a V6 is less well balanced than a straight 6, though I'll admit that's something I learned on this thread.
From reading the other posts, it seems far less clear which is the best balanced out of a straight 4 and a V6 - and that's just from a moving-mass point of view. Add in the much larger combustion forces and it's no contest.
I saw it as a generalization rather than an absolute.
Actually, thinking more about it, you'd want it to be most effective somewhere below full power, so the area under the curve of reduced vibration, across the entire operating range, is minimized.
Nope, nor does my non-balance shafted I4. (2.0L in an '86 900). So there's more to it than either of us are considering. I'm thinking the engine mounts are coming into play.
But, have we determined how much of the overall vibration that force is? That'll be pretty colinear with the axis of the bore, wouldn't it? The "jumping up and down" that someone else mentioned. Linear forces should be easier to dampen than forces in several directions.
That's the thing - tried it this morning in my non-balance-shaft 2.0L, and the absence of vibration to the pedal, or the gearshift, is equally low regardless.
I think you assumed what I was saying. They're obviously optimized _at some point_, most likely where it'll do the most good.
I assure you, marketing morons don't care about anything other than what color it is.
OK, I'll say that the 4 with balance shafts can be smoother than the 6 without balance shafts. Throw 4 balance shafts into the 6, then the 6 will probably be smoother, because then _all things are more equal_, and then, at that point, the fact that 6 is bigger than 4 comes into play.
I don't know that a 1 or 2 anything is really in-scope, because they present unique challenges as has been mentioned. a I-3 two stroke would be in scope for Saabs, and there is quite a bit of tortional vibration at idle, but that's more the nature of a 2-stroke's scavenging than anythign else.
I think that's pretty key there.
If you can't feel it, does it matter if there's vibration? Sometimes, "good enough", is.
I'll see your pre-emptive strike, and raise you a dose of gratuitous sillyness.
No, that's what *I* have been saying all along. I think. Damn, now I think I have you confused with me. Or the other way around; yes, that's more likely. Seriously though, let's take a different look at this. What, other than internal stresses, would account for the Saab High Milage list over at (evilplace) having a whole lot more 4's than 6's? Market share is part of it, but I wonder if it's disproportionately skewed towards the I4 during the years when both were offered. I'd bet a pint that it is.
Not if you're saying one is more "harsh" than another; since that's a human-based measurement, the only vibration that matters in that context is what the human can observe in normal operation of the vehicle.
Then you'd have an engine with it's vibration minimum at some point between overrun an maximum output. Again, that would be really easy to spot. All the piston engines I've come across vibrate most at full power and least on overrun.
It seems to fit perfectly with my view that the balance shafts are only there to balance the moving masses.
No. There's a torsional component too - the counter-torque to the torque pulses applied to the crank by the rods.
Was that double negative deliberate ;o)
I feel the increase in mine alright. It never goes to irritating levels IMO, but the increase is unmistakable.
And that point is overrun.
Level playing fields and all that. Then again, no manufacturer that I know of seems to feel the need for a balance-shafted V6, whereas quite a few have gone for balance shafts in their straight fours.
It's not in-scope at-all other than as a demonstration that when engine designers have a choice between reducing inertial vibration or reducing combustion related vibration, they go for the one that will give them the most benefit - combustion vibration.
Nope. This discussion is pretty academic as far as the real world is concerned.
Sometimes, yes.
I'd have to bow out of that one. No experience. I think you'd be stretching it a bit to suggest that it was all down to a catastrophic lack of balance though.
If you insist on bringing engine mounts into it, then you also need to add the seat foam, the sound deadening materials, the carpets, the resonance of the ashtrays, the Youngs modulus of the gear lever gaiter etc. etc. No point going at it half-cocked is there?
I can personally tell you the GM V6 in the Saabs are among the roughest idling engine around. The I4 Saab engine is much smoother. My I4 Saab engine has more power and gets better gas mileage. I bought a Saab V6 for my daugther to learn to drive. It was cheap beause no one wants them, so when it gets damaged in the hands of a beginning driver, there will be no tears shed. I own and drive both, a real Saab with an I4 and the GM V6 Saab. From my personal experience, the V6 GM engine sucks in comparison to the I4 Saab engine. But, like I said, the V6 Saab was cheap - the same car/same year with an I4 engine sells for $2,000 more.
To summarize, I have seen and driven a Saab V6 and I do know it's problems. . .
OK...so you're saying that Saab is destined only to sell cars to people who live where it snows a lot??? That's fairly self-limiting and I don't agree that that's what Saab is all about...especially since it sells a popular convertible model.
I'd get used to the idea. I've heard rumors that a RWD car is not far off in the future for Saab, particularly if GM wants its "premium luxury brand" to compete against BMWs and Audis. While an AWD model would be ideal, I don't think that Saab has the kind of financial/time resources to develop one on its own (I don't seriously view the 9-2x as part of that equation).
Not at all. The iffy benefits of RWD in ideal conditions aren't worth contaminating the brand for. The real benefits of FWD in everything but perfect conditions is why Saab has always been FWD.
Well, since it's your point and not mine, I'm not going to disagree that it's a bad one. Please don't try to tell me what my point is and then why you disagree with it; that's a cheap rhetorical tactic.
What does a roof have to do with where the driven wheels are?
If it's RWD, it won't be an actual Saab, it'll be a badged thing like the Saaburu.
That's how I feel about any RWD they try to pretend is a Saab. If you want a nice RWD, consider a Volvo or a Beemer.
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