I agree that gearing is what brings the engine rpm into the proper range
to generate the needed torque for towing and that gearing is a fairly
important factor for non-turbo non-diesel engines. If you've read the
following article, you realize that torque is the ability to do work (i.e.
pull a trailer through the wind or up a grade) and hp provides the ability
to do work quickly (i.e. acceleration to pass another vehicle or get up
to speed to merge into traffic from an on ramp.)
Towing - horsepower versus torque
For turbo engines and diesel engines most of the engine torque is
available at much lower rpms.
For towing at 60+ mph with our Honda CRV, we often needed to use
the D3 setting on the transmission. That locked out overdrive gearing
and immediately jumped the engine rpm up beyond 3000 rpm.
(Remember that the Honda CRV developed its best torque of
163 lb-ft @ 4400 rpm). Compared to the normal non-towing rpm
of below 2000 rpm, my wife always said that it sounded to her
like the CRV engine was "racing" when we were in D3.
Looking at the torque curve for the Ford 2.0L EB engine, in the
following article, you will see that, at 1700 - 2000 rpm, the Ford
2.0L EB engine generates the same or more than the max
torque of the CRV. A similar high-torque@low-rpm characteristic
is probably available with most of the small diesel engines.
Stout EcoBoost I-4 Plays Well Above Weight Class
With 270 lb-ft of torque and 140 hp, I would expect that the
VW JSW would tow quite nicely and get great economy, but
might not be too quick in passing or accelerating into traffic
from an on ramp. (I don't know that to be true; it would just
be my guess from the stats.)
When we are towing at ~60 mph in the D gear of our Ford Escape
the engine rpm is around 1700-1750. If I put the 6-spd SelectShift
transmission into S or S5, the rpm goes up to about 2250. If you
look at the torque curve for the Ford 2.0L EB, you'll see that we
are getting most of the engines torque in those ranges.
Since the OPs original question was about towing a Scamp16 with
a small diesel, I wish I had the torque curves and 60-mph RPM
ranges for the vehicles that he is considering. Although the general
torque and hp stats are available on sites like Edmunds.com and
Cars.com, I have sometimes found it a little difficult to come up
with the actual torque curve for various engines/vehicles.
Again ..... just my 2 cents worth. As always, YMMV.