More cylinders/V-engine = longer engine life than fewer cylinders/Inline?

[yachtie]

Originally Posted by Huntsman

Remember, too, that V-12s are generally quite high performance affairs, and there are not that many of them. 6s and 8s are a dime-a-dozen in any number of output levels. I knew someone would bring up the flats. Ok, this isn't really all that simple. We had a lively debate in Advanced Thermo on this. There are two main kinds of 'flat' engines, the Boxer and the 180 deg V. They are not equivalent in terms of balance. 1) The Boxer, in which the cylinder motion is mirrored across the crankplane, i.e, both cylinders in each bank are at TDC and later BDC at the same time. For this to be possible, imagine the cylinders at BDC, closest to the crank. Where are the con rod big ends? If the cylinders are perfectly opposed the big end bearings would be occupying the same space, which of course cannot be. Therefore Boxers do not have perfectly opposed cylinders in each bank, they are offset slightly, requiring (as the defining feature of a Boxer) separate crank journals. Now even though the pistons move in opposite directions (inducing primary balance), there is a free secondary couple (erm, tied rotational forces) caused by that cylinder offset. That couple acts to rock the engine around the vertical axis (that is, about an axis normal to the cylinder plane). So while all Boxer configurations can have inherent perfect primary balance, that's kind of big whoop. Secondary balance is much more challenging to achieve, and Boxers can by canceling out the couples with enough cylinders. The Boxer-4 is not perfectly balanced. I think the six is. 2) The 180 degree V. The difference between a Boxer and a 180 degree or flatplane V is that the cylinder motion is not mirrored across the crank. One cylinder in a bank is at TDC while its twin is at BDC, resulting in (just like a crossplane V) two big ends per crank journal. Obviously then, perfect primary balance is not achieved for all configurations. Again, add cylinders to fix this problem. The 180 deg V-6 should be (I think), and I know that the 180 degree V-12 is balanced. However, that is for the same reasons that the V-12 is balanced, not because it is a flat engine. I'm also reasonably certain that the Testarossa uses a 180-V and not a Boxer. 3) Explanations like this are when I wish I was a better kinematician. No clue about the W's. ~ H
IIRC no W-engine is naturally balanced 45 degree V-16's are perfectly balanced as are 60 degree V-12's. Straight sixes and eights are balanced as well. In my personal experience it's not the number of cylinders as much as the engine speed that affects lifespan. Hi revs = short life.

 

[Huntsman]

Originally Posted by yachtie

IIRC no W-engine is naturally balanced 45 degree V-16's are perfectly balanced as are 60 degree V-12's. Straight sixes and eights are balanced as well. In my personal experience it's not the number of cylinders as much as the engine speed that affects lifespan. Hi revs = short life.
I know nothing about the W's, can't even imagine it. But I would presume that a W24 would be balanced! I was surprised about the I8. I didn't think it was balanced inherently, as I know Duesenberg employed two chambers with 1/2lb of mercury at either end of the crank as dynamic dampers on their SJ and J Straight 8's. Apparently, it can be done only with some sneaky timing -- using the best 4cyl configuration and mirroring that across the crank balances out the primary moment that is left unbalanced in the I4. Interesting. I would be prepared to state that V-12s at all V angles are perfectly balanced. If an I6 is perfectly balanced, how can sticking two of them together not be? I would tend to agree that the oversquare hi-revving engines would have shorter life -- especially if the lubrication cannot keep up. ~ H

 

[eg1]

Originally Posted by yachtie

IIRC no W-engine is naturally balanced
45 degree V-16's are perfectly balanced as are 60 degree V-12's. Straight sixes and eights are balanced as well. In my personal experience it's not the number of cylinders as much as the engine speed that affects lifespan.
Hi revs = short life.

Originally Posted by Huntsman

I know nothing about the W's, can't even imagine it. But I would presume that a W24 would be balanced!

I was surprised about the I8. I didn't think it was balanced inherently, as I know Duesenberg employed two chambers with 1/2lb of mercury at either end of the crank as dynamic dampers on their SJ and J Straight 8's. Apparently, it can be done only with some sneaky timing -- using the best 4cyl configuration and mirroring that across the crank balances out the primary moment that is left unbalanced in the I4. Interesting.

I would be prepared to state that V-12s at all V angles are perfectly balanced. If an I6 is perfectly balanced, how can sticking two of them together not be?

I would tend to agree that the oversquare hi-revving engines would have shorter life -- especially if the lubrication cannot keep up.

~ H

I would guess that this is the genesis of the "more cylinders equals longer life" concept, since V8s and other larger engines can run at highway speed with lower RPMs than smaller engines (though this ignores the actual volume of the cylinders).

 

[A Y]

Originally Posted by Huntsman

I would be prepared to state that V-12s at all V angles are perfectly balanced. If an I6 is perfectly balanced, how can sticking two of them together not be?

Perhaps Yachtie was thinking about the smoothness of the engine's power pulses. V12s at integer multiples of 60 degrees are very smooth.

--Andre

 

[Conrad]

There are way too many factors to come up with any reasonable estimate of how long an engine will last in anything.

One run at higher speeds will last less time than one run at low speeds.

One run at constant speed and load will last longer than one run at variable speed and load.

One that sees frequent cold starts and short trips will not last as long as one that is allowed to warm up every time it's driven.

One better maintained will last longer.

And that's just the beginning of it.

I've seen plenty of 4, 6, and 8 cylinders of all descriptions live short, horrible lives.

I've seen plenty that have no reason to still be running, but just won't die.

Just tell him to find a car that's in nice shape and has maintenace records. That's really the best he can do.

And as for V versus inline and life span, look up the Ford 300-6. The 300 is probably the most legendary durability motor the world has ever seen. Lifespans in excess of 350,000 miles are VERY common. They're also the most common gas engine found in airport tugs and have been for at least 30 years. Then look up the Chevy 250 and the Chrysler 225- probably the next two most durable gasoline motors ever built.

However, i'm willing to bet most of it has to deal with the old I-6's only operating at 3500 RPM and less. Wear increases exponentially with RPM.

 

[yachtie]

Originally Posted by Huntsman

I know nothing about the W's, can't even imagine it. But I would presume that a W24 would be balanced! I was surprised about the I8. I didn't think it was balanced inherently, as I know Duesenberg employed two chambers with 1/2lb of mercury at either end of the crank as dynamic dampers on their SJ and J Straight 8's. Apparently, it can be done only with some sneaky timing -- using the best 4cyl configuration and mirroring that across the crank balances out the primary moment that is left unbalanced in the I4. Interesting. I would be prepared to state that V-12s at all V angles are perfectly balanced. If an I6 is perfectly balanced, how can sticking two of them together not be? I would tend to agree that the oversquare hi-revving engines would have shorter life -- especially if the lubrication cannot keep up. ~ H
The J and SJ Duesies had a mercury damper for torsional vibration- crank would twist and un-twist without it. Nothing to do with balance, just a very long crankshaft. Better engineering IMO than Bugatti's "just make it so big that it can't twist" theory. For v-12's the pulse timing is off if you don't go with 60, 120 or 180 degrees. You're correct about crank balance.

 

[dtmt]

Originally Posted by Tck13

I'm talking about ALL models of Subaru before the latest engine. Anyone know what Im talking about or is it just me?

I've mentioned it in passing on the Subaru's forums and I was told that the latest engine was adequate (which I test drove and liked) but others agreed that the older engines were very slow... I didn't ask why...

Subaru has been building the turbocharged Impreza WRX since 1992, so yeah, it's just you.

 

[Conrad]

W's are unique creatures, there are just too many ways to lay them out to say "all X cylinder W's are balanced". The VW W-12 is naturally balanced as it is two VR6's offset to 60*. Therefore, it acts like a 60* V-12

The original W-12 was the Napier-Lion which was three banks of 4 offset 60*, so it acted like two 60* V-8's which would not produce balance on the second order.

As for a W-24, in theory it would have the advantage over a V-12 of balancing on every 30* increment instead of every 60*. However, all W-24's that have been attempted have needed two separate crankshafts, so it's really just two 60* V-12's running simultaneously.

For a shared crank 24 cylinder, look up the X-24. That there is a unique creature.
all kinds of weird layouts out there.

 

[Tck13]

Originally Posted by dtmt

Subaru has been building the turbocharged Impreza WRX since 1992, so yeah, it's just you.

Is it clear that I'm not talking about a supercharged engine?

 

[dtmt]

Originally Posted by Tck13

Is it clear that I'm not talking about a supercharged engine?

Ok, so what you're saying then is that all Subarus are slow, except for the fast ones. Yup, makes total sense.

 

[Tck13]

Originally Posted by dtmt

Ok, so what you're saying then is that all Subarus are slow, except for the fast ones. Yup, makes total sense.

I just did a google search and got my answer. I'll definitely remember to do that first the next time. kthxbai