[aunty_helen]

I always find it interesting that when hp/l stats are quoted they often neglect to include motorcycle engines... which have been in the 180-210 hp/l realm for about 5 years now.

And a high hp/l isn't necessarily the best piston engine as it's often at the cost of massive valve train losses resulting in poor fuel efficiency.

[bradleyland]

It's difficult to compare the specific output of engines of dramatically different displacement. As a general rule, displacement and specific output are inversely correlated. That's not to say that motorcycle engines aren't an absolute marvel of engineering and technology, but it's not possible to compare them directly to engines with twice the displacement because you can't simply scale up the motorcycle engine and get the same results at the larger displacement.