Diesel _tends_ to be around 25% more efficient for the same power output,
given allowances for gearing and such like. They _tend_ to go around 25%
further from a given volume of fuel. There are exceptions to every rule of
For a given power output, *with optimised gearing,* performance is
Diesel dislikers criticised turbodiesels for having a narrow power band.
You might have a power band of say 2,000 rpm to 4,500 rpm. Petrol engine
haters dislike the way you often need to see 4,000 rpm on the tacho to get
into the proper power band. 4,000 rpm to maybe 7,000 rpm isn't much wider
than the diesel power band... again subject to the vagaries of engine
design and gearing (cue a bunch of arguments that some petrol engines have
much broader power bands).
The above arguments may be negated by optimised gearing. As it happens,
many modern turbodiesels are sitting in their (limited it may be) power band
at a motorway cruise in top gear. Relatively few petrol cars are. That
might make the turbodiesel quicker in top but not quicker full stop. Here's
where the driver (or transmission) but change down...
Drive an automatic diesel with a set up transmission back to back with a
same power output automatic petrol with an equally set up transmission, both
with the same power, both will have comparable performance. Except one will
sound whiny and drink funky smelling stuff, whereas the other, hmm nice
rumble and lovely sticky derv to wipe on your shoes... hmm... diesel...
Sorry. Got a bit off topic there. :-)
Most diesels these days are turbocharged, thus produce on paper more torque
than their petrol peers, but the relevance to on road performance is tied in
with the above. More torque at the donk, taller gearing, reduced impact at
Diesel engines tend to be heavier than their petrol counterparts, power for
power, thanks to more use of cast iron blocks.