Tim Dickson, who is Autocar’s letters editor among other jobs, sent me this interesting note from reader Chris Smith of Tunbridge Wells:

Dear Sir, Engine down-sizing, turbocharging, improved economy – all the current trends that we see throughout the industry – from a Fiesta to a Bentley this is the overwhelming target of the manufacturers.

However, in pulling up carpets in an old house I came across the attached advert from 1981 – the points being made could be used verbatim in an advert today!

The Renault 18 Turbo advert boasts an amazing 44 petrol mpg at 56mph. The small print says the period ‘Government Test Figures’ gave a ‘simulated urban cycle’ mpg of 28.8 and a 33.2mpg at a ‘constant 75mph’.

Aside from the amusing £6589 price tag (which includes the 15 per cent VAT levied at the time) does anybody remember whether petrol cars from 30 years ago could really return such respectable economy figures, turbocharged or not?

Of course, cars of this period were much lighter, though many had all the structural integrity of a wet cardboard box. And they also lacked the anti-pollution kit that, initially at least, made petrol engine economy worse.

The EU economy test came in during the mid-1990s and was supposed to be much closer to real-world conditions. As far as I can remember, the old simulated urban cycle was usually hopelessly over-generous.

Does anybody have some real economy figures that prove petrol engines have made surprisingly little gain in economy over the last three decades? Or is it just a case of cars getting far heavier, blunting the improvements in petrol engined technology?

Oh, and why was the old high-speed test conducted at 75mph when the speed limit was 70?