Does anyone else like driving fast?

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At the time manufacturers were allowed to enter 4 stroke engines of up to 990cc with 3-6 cylinders.

Adding an extra cylinder increases valve space, meaning more fuel/air mixture can enter the cylinder.
It also means the each cylinder can be 20% shorter for the given displacement, reducing the distance the piston needs to travel and thereby increasing redline.

Shorter stroke means higher redline, better breathing means additional power up top.
Both factors should cause the 5 cylinder engine to produce more power than a 4 cylinder engine of similar displacement.

While a 6 cylinder engine should be the most powerful design within the limitations, it may have been more difficult to package in the required size. Engines with fewer cylinders weigh less and produce more torque and may also have superior fuel economy.

I found this intriguing so I looked for a photo. One thing that struck out at me looking at photos is that unlike most V engines, the cylinders are not opposed to each other, rather arranged in a W pattern when viewed from above. Also instead of having 2 separate and angled cylinder heads like a typical V engine the V5 appeared to be of a single flat head design and the head design appeared really simple. The advantage I see of that would be much lower manufacturing costs and some material savings. Of course the compactness as you mentioned is always a good thing, especially in FWD applications where space is tight. Genius piece of engineering although the connecting rods much be on quite the steep angle.

I found this intriguing so I looked for a photo. One thing that struck out at me looking at photos is that unlike most V engines, the cylinders are not opposed to each other, rather arranged in a W pattern when viewed from above. Also instead of having 2 separate and angled cylinder heads like a typical V engine the V5 appeared to be of a single flat head design and the head design appeared really simple. The advantage I see of that would be much lower manufacturing costs and some material savings. Of course the compactness as you mentioned is always a good thing, especially in FWD applications where space is tight. Genius piece of engineering although the connecting rods much be on quite the steep angle.

I hadn't thought of the W thing, that is thinking outside of the box. so instead of a lopsided V engine it is more reminiscent of a zigzag engine.

With a VR you're right though, that there's overlap between cylinders and the cylinders sorta zig-zag across each other.

I couldn't tell in the pictures, but is there a balance shaft hiding in there someplace? and if not how do they tame the vibration?

When comparing piston engines with different configurations in the number of cylinders, the V angle, etc., the term "inherent balance" is used. This term often describes just two categories in the above list that are 'inherent' in the configuration, namely, 3. Phase balance on reciprocating mass, and 13. Phase balance on torque generation.

In rare cases when considering a boxer twin, the categories 4. Plane balance on reciprocating mass, 6. Plane balance on rotating mass and sometimes 14. Plane balance on torque generation are included, however, statements like "A flat-8 boxer engine has a perfect inherent balance" ignore these three categories (as well as 16. Plane imbalance on compression) as flat-8 boxer configuration has inherent imbalance in these four categories by having the left and right banks staggered front to back (not positioned symmetrically in plan view) in the same manner as in boxer twin.

"Inherent mechanical balance" further complicates the discussion in the use of the word 'mechanical' by implying to exclude balances on torque generation and compression for some people (as in the above categorization) while not excluding them for others (as they are the results of mechanical interaction among piston, conrod and crankshaft).

While many items on the above category list are not inherent to a configuration of a multi-cylinder engine, it is safe for a meaningful discussion of inherent balance on multi-cylinder engine configurations to include at least the balances on:

-Reciprocating mass (3.Phase and 4.Plane)
-Rotating mass (6.Plane)
-Torque generation (13.Phase and 14.Plane) and
-Compression (15.Phase and 16.Plane)

...

Inline five cylinder (L5) engine, with crank throws at 72° phase shift to each other, is the common five cylinder configuration. Exceptions are Honda racing V5, and Volkswagen VR5 engine. These typical L5 engines have 13. Evenly spaced firing and perfect 3. Phase balance on reciprocating mass, with 4. Plane imbalance on reciprocating mass, 6. Plane imbalance on rotating mass, 14. Plane imbalance on torque generation, and 16. Plane imbalance on compression. Just like in inline 3 engines above, these first order rocking couples can be countered with heavy counterweights, and the secondary balance is comparable to, or better than an ordinary inline 6 because there are no piston pairs that move together.

Compared to three and four cylinder designs, a major advantage in 4-stroke format is the overlap in power stroke, where the combustion at every 144° of crank rotation ensures a continuous driving torque, which, while not as much noticeable at high rpm, translates to a much smoother idle.

Modern examples such as the 2013 Audi RS3 engine have undersquare design, because the advantage in secondary balance allows it to have longer stroke without sacrificing the higher rpm smoothness, which is desirable for a smaller bore that results in shorter engine length. Honda G20A also with an undersquare design, was originally introduced with a balance shaft driven at the crankshaft speed to counter the wiggling vibration caused by the 6. Plane imbalance on rotating mass, but it evolved into 2.5 Liter G25A with heavier counterweights that does not have the balancer.

rather than make complicated aftermeasures [advanced active motor mounts, balance shafts, electronic vibration control et al] for rough-running motors, why not instead start out making a SMOOTH motor?

Because only V12s, I6s and flat 6s can be perfectly balanced, all other configurations have an inherent imbalance.

can't a pancake or inline 6 be made small enough for all applications?

It doesn't seem to be possible, at the very least the drawbacks seem to outweigh (size and packaging for example, but also sixes are thirstier than fours) whatever advantages there would be. If it was advantageous to use perfectly balanced engines in all applications that's what companies would be putting their focus into. Since they're not it seems unlikely to be feasible.