On 05/03/2017 20:15, Chris Green wrote:
I *think* if you compare a diesel at a steady 70mph on the motorway
with a similar powered petrol engine at the same speed there's very
little to choose between them. It *used* to be that the petrol engine
was more economical but maybe the pressure to make better diesel
engines has meant that they've caught up.

It's a great pity that the 'lean burn' developments of petrol engines
petered out.

My son does silly mileage in a Mazda petrol. It's amazingly economical
on a motorway cruise - must do something odd like lean burn.

It also has a 15:1 compression ratio!

Andy