wrote:
If the HP/weight ratio is similar to aircraft engines designed from
scratch then we shouldn't be so quick to dismiss it. A much
higher weight efficiency would seem improbable though.

Well... using the 120hp takeoff rating and 200lbs, 0.6 hp/lb sounds
right as a takeoff rating. 84hp continuous seems like good,
conservative engineering.

Comparable popular engines of similar output like the O-235 (approx
0.55hp/lb), 912 (between 0.55-0.65 hp/lb depending mostly on which
version, 80hp or 100hp), Jabiru 3300 (approx 0.65 hp/lb).

Now, the devil is in the details. I suspect "200lbs" does not include
the radiators and plumbing. In the catalog (6MB download), cited
earlier in this thread by JP, down at the bottom of page 7, there is a
note about the engine weight figures (note, they do include reduction
drive). Anyway, leaving off the radiator weights makes the power:weight
figures less optimistic and more believable.

I think the major reasons for the improved output are
1) the liquid cooling allows a higher compression ratio
2) improved heat dissipation over the well known cooling fin limitation
on VW heads

Just my thoughts. My VW experience is that I rode in a Bug once or twice