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      11-16-2013, 12:41 PM   #1
dparm
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Question Magical ratio of 0.5L per cylinder

Something that I've noticed about BMW: many of their motors have 0.5L of displacement per cylinder:

I-4s are 2.0L
I-6s are 3.0L
V-8s are 4.0L
V-10s are 5.0L
V-12s are 6.0L

There are a few exceptions, such as the current turbo V-8 that's 4.4L, but in general they adhere to the sizing I described above. Even their upcoming I-3 is 1.5L.

Is there some benefit to that "magical ratio"? Or is this done for ease of manufacturing/engineering, i.e. parts sharing? Audi does it a bit too.
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      11-16-2013, 03:55 PM   #2
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that displacement provides the best balance between power and torque which most road cars are wanting...

smaller displacement allows for higher revs/max power output but will suffer low torque and the vice verca...

The bore and stroke also play a part in engine balance too which is another consideration in a road car
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      11-18-2013, 10:39 AM   #3
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You'll notice the higher-rev'ing the engine, the shorter the stroke and larger the bore. Shorter strokes generally lead to less torque but the ability to rev higher.

Hence why the 2.4L V8's in F1 are all 300cc combustion chambers rev'ing to 18k.

Keeping the chamber volume the same saves on a lot of development costs as well.
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