Originally Posted By: Eddie
Not a smooth running engine.
^^ This.
Here is an explanation based on my understanding:
Flat-plane crank V8s inherently generate 2nd-order vibration. They work best when they have super-lightweight internals, a short piston stroke, and a high rod/stroke ratio, because those make the vibration much less severe. Those attributes are best suited to small, lightweight engines with stratospheric redlines and lots of top-end power -- in other words, race engines.
Street engines tend to put a higher emphasis on low-end torque, low NVH, and cost control, so a cross-plane crankshaft is better suited. Balance shafts can eliminate the NVH problem for a flat-plane crank V8, but they are complicated to implement and their extra mass largely cancels the benefits of having a flat-plane crank in the first place.
Now, all of that being said, I share your wish for more flat-plane crank V8s. I would happily give up some low-end torque and tolerate some extra vibration in exchange for a huge redline and a screaming top-end.