The primary reason to use a V-engine is largely packaging. They're shorter and more compact than an inline engine.
However, you're getting to the really fun stuff and that's the bank angle and phasing. The first thing to consider is an engine as a purely rotational system. Imagine a one cylinder engine; the rotating crankshaft is massively out of balance. Even if the actual crankshaft was perfectly balanced, the motion of the piston and the forces it applies will never cancel out. This is why most one cylinder engines run a balance shaft; a weighted shaft geared into the crankshaft to mitigate the out-of-balance effects. A balance shaft can be run on other out of balance engines as well.
A V-engine, on the other hand, can be made to be inherently balanced. This means that no matter what speed the engine's running at, the forces from the rotating assembly will always cancel out. Most notably, a 90 degree V4 or V8 engine can be easily balanced and many race motorcycle engines use this configuration (Honda and Ducati in MotoGP). V6s and V12s run balanced at 60 degree bank angle.
Note that I say 'can' be better balanced. This is because you also have to look at your firing orders and phasing. Back to MotoGP, we can look at the Honda NSR500 2 stroke race bike of the '80s and '90s. They ran that engine as an even-fire engine (over 360deg of rotation for a 2 stroke or 720deg of rotation for a 4 stroke), the cylinders fire at even intervals. So if it's a 4 cylinder, they fire every 90 or 180 degrees. # of cylinders/cycle length=cylinder phasing. This is the most ideal way of running an engine and will provide the inherent balance
However they also ran that engine as a big bang engine. By building new crankshaft and camshafts, they made it so that all pistons fired within 72 degrees of each other. This was done for non-engine reasons, tire dynamics actually, but it's a good example of how you can change phasing.
An interesting note: because a V12 is essentially two inline 6 engines stuck together they're naturally balanced regardless of bank angle. This is why V12 Jaguars have a reputation for smoothness. V6s, being two 3 cylinders stuck together, are inherently out of balance.
However, you're getting to the really fun stuff and that's the bank angle and phasing. The first thing to consider is an engine as a purely rotational system. Imagine a one cylinder engine; the rotating crankshaft is massively out of balance. Even if the actual crankshaft was perfectly balanced, the motion of the piston and the forces it applies will never cancel out. This is why most one cylinder engines run a balance shaft; a weighted shaft geared into the crankshaft to mitigate the out-of-balance effects. A balance shaft can be run on other out of balance engines as well.
A V-engine, on the other hand, can be made to be inherently balanced. This means that no matter what speed the engine's running at, the forces from the rotating assembly will always cancel out. Most notably, a 90 degree V4 or V8 engine can be easily balanced and many race motorcycle engines use this configuration (Honda and Ducati in MotoGP). V6s and V12s run balanced at 60 degree bank angle.
Note that I say 'can' be better balanced. This is because you also have to look at your firing orders and phasing. Back to MotoGP, we can look at the Honda NSR500 2 stroke race bike of the '80s and '90s. They ran that engine as an even-fire engine (over 360deg of rotation for a 2 stroke or 720deg of rotation for a 4 stroke), the cylinders fire at even intervals. So if it's a 4 cylinder, they fire every 90 or 180 degrees. # of cylinders/cycle length=cylinder phasing. This is the most ideal way of running an engine and will provide the inherent balance
However they also ran that engine as a big bang engine. By building new crankshaft and camshafts, they made it so that all pistons fired within 72 degrees of each other. This was done for non-engine reasons, tire dynamics actually, but it's a good example of how you can change phasing.
An interesting note: because a V12 is essentially two inline 6 engines stuck together they're naturally balanced regardless of bank angle. This is why V12 Jaguars have a reputation for smoothness. V6s, being two 3 cylinders stuck together, are inherently out of balance.
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