The message
from Andy Dingley contains these words:

60 bhp per litre. The same as a '64 Mini Cooper S. Just what you'd expect
from a modern truck engine. Proper sports car engines manage over 100 bhp
per litre.

Well racing car engines possibly. Not many road tuned cars will do it.

100bhp / litre was the mark of a "tuned" car 25 years ago and it often
meant something that had a lumpy idle and didn't deliver until 3000 rpm.
These day's it's just hot hatch territory and 120bhp / litre is nothing
unusual for a perfectly well behaved road car.

I have missed the earlier part of this thread but proper sports cars
back in the 60s an early 70s were mostly way below 100 bhp per litre.

The Lotus Elan at 1600cc as introduced in 1962 had a claimed output of
105 bhp and the figures got worse over the years before they got better.
The S4 std, s/e, Sprint were 90/93/126 respectively and it has since
been alleged in some quarters that at least some of the figures had been
either exagerated or resulted from especially tuned engines. The Lotus
BRM, essentially the prototype Sprint was supposedly 130 bhp but that
didn't have a rev limiter at 6500 rpm while the Sprint reached maximum
power right on that rev limit.

Most of the sports cars of the period were much less powerful both in
power/weight ratio and specific power output per litre. The Elan Sprint
is one of the few cars of the era that can see off todays hot hatches.
Geoffs E Type may be another. Things like MGBs are really pedestrian (I
had a friend in the 70s who reckoned the MGA was a better car) and
Spridgets were a joke sports car from inception. Donald Healey claimed
(back in the 40s I think) that sports cars (even then) should have a
power to weight ratio of at least 100 bhp per ton. It was debatable with
the first of the Austin Healeys, the BN1 100/4 (introduced 1952 IIRC)
and none of the Spridgets (Sprite introduced 1958) came anywhere close.
Almost any modern shopping trolley will see off a Spridget, at least in
a straight line.

--
Roger Chapman