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Just been wondering today about this,

has anyone ever built a 90 degree Inline Four Cylinder engine?
Would it differ from a V4 engine?
I assume it would essentially be a Zero Degree V4?

And for that matter, what does the Degree of Offset on a V-shaped engine affect?
 

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I4 stands for Inline 4. As in all four cylinders inline. You can't have them offset by 90 degrees and still have an i4.
It's a semantics thing regarding the shape of the crankshaft. For example, Ferrari once made a 180 degree v12. Looks like a flat-12, but the crankshaft shape made it behave like a v engine.
 

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Yep, "crossplane" is what you're thinking of. It simply means each adjacent crank lobe is evenly rotated (realtive to 360*) from the one next to it. So on a i4, each lobe is 90* offset from the one next to it. On a triple, it's 120*.

I've ridden a newer crossplane R1, and the engine definitely has a different character. It's very smooth and has better low end torque than you'd expect, along with a very "even", almost burbling exhaust note.

The trade off is that peak power isn't as good as a traditional layout, the R1 consistently places last in literbike shootouts in terms of raw performance. It also creates more vibration compared to a flatplane (traditional) so they usually need balance shafts.

In theory it's better for durability as well, smooths out the power pulses on the rod and crank bearings so less peak force endured.
 
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