Ferrari Boxer Engines and Flat Cranks

A question was brought up as to why some of the 12-cylinder Ferrari engines are called V12 when they are actually flat (non-V shaped). The reason is because the flat engines are a 180º V12! If you're new to Ferrari engines then this is a bit confusing. Here is what I learned and I hope it will help other newbies...

The following information is mostly from threads taken from www.ferrarichat.com and I have edited it for content and clarity.

First, let's get some basic definitions in place so we're speaking the same language.
TDC: Top Dead Center, when the piston is at the top of its stroke (closest to the spark plug).

BDC: Bottom Dead Center, when the piston is at the bottom of its stroke (furthest away from the spark plug).

Cross-plane crank: The crank pins are 90º apart. Your typical modern Ford, Chevrolet, and Dodge engines in the V8 configuration use this style of crank.
Here's an example of such a crank:


Example of a cross-plane crank in action.	Cross-plane crank. Crank pins are 90° from each other.

Flat-plane crank: The crank pins are on opposite sides of the crank centerline - 180º apart. All the pisons on one bank reach TDC or BDC at the same time.
Thus, the firing order on a flat-plane crank alternates between banks -- on a cross-plane crank it usually doesn't so you periodically get sequential exhaust pulses into the same exhaust side giving the "muscle car" rumble in a dual exhaust. More information is here and here.

Flap-plane crank. Crank pins are 180° from each other.

In-line engine: All the cylinders are lined up in a row. An example would be most modern 4-cylinder imports like the Honda Civic or Volkswagen Golf.
Here's a typical in-line engine...and notice that it's a flat-plane crank:

Inline 4 animation

V engine: When viewed along the line of the crankshaft, the pistons are aligned in the shape of the letter "V". Again, your typical V8 American engine.

Boxer engine: There are two thoughts about what a "boxer" engine is.
1) In the very broadest sense of the word, it's an engine where the cylinder banks are on the same plane as the crank, or 180º separated from each other.
2) More specifically, it's horizontally opposed where the corresponding pistons reach TDC (and also BDC) at the same time because they do not share a crank pin (each piston has its own crank pin) AND it uses a flat-plane crank. They're moving in or out at the same time.
Example of a horizontally opposed boxer motor, like what you would find in an old air-cooled Volkswagen:

Boxer animation

Lastly, do not confuse flat-plane (crank) with flat (or boxer) engine! An engine can be flat but use an non-flat-plane crank. For example, a 12-cylinder engine can be flat but it will use a crank where the crank pins are spaced 60º.

So what is a Ferrari 180º V12?
Well, you could say it's a V12 engine that had its V spread apart and flattened so that the angle between the arms of the V are 180º apart

In this type of Ferrari engine the "180º V" is describing the cylinder orientation only; because each crank pin shares two pistons it would be more accurate to label the 180º V12 as a flat engine. Remember, a boxer engine has only one piston per crank pin.

Here's a good visual example that FerrariChat member DGS provided:
Figure 1 displays the boxer engine (each piston has its own crank pin) while Figure 2 displays the 180º V (the pistons are sharing a crank pin). In a 180º V with a flat crank (Figure 2), opposed cylinders hit TDC 180º apart. So when one piston is at TDC, the opposed cylinder is at BDC. They both move to the right or left (relative to the engine centerline) at the same time. In a boxer engine (Figure 1), the opposed cylinders do not share the same crank offset, and they hit TDC at the same time. They're both moving in or out at the same time.

Figure 1. Boxer engine. Two crank pins.
Figure 2. 180º V engine. One crank pin.

So what about the Ferrari engines that are labeled with with word "boxer"? Well, the use of the word doesn't mean that it's being used correctly. For example: With the 512BB, the "BB" stands for "Berlinetta Boxer". Though the cylinders are in a flat orientation like a boxer engine, is really a flat engine (180º V) because the pistons of this particular engine share a crank pin. If each piston had its own crank pin then it would have been a true boxer motor. In these situations the cylinder configuration as well as the crank throw angles must be determined before labeling an engine a true boxer (180º V with flat-plane crank, Figure 1) or just a flat engine (180º V, Figure 2).

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