Economy - not a word you'd expect on a website crammed with muscle-car information, but we reckon that the fact that our chancellor wants to push petrol prices up approaching £1 per litre may be making folks think twice about a Mustang.

It's confession time.  My daily drive  is a 193bhp 2.8 litre straight six BMW that's now covered 200k miles.  It gets 28.2 miles to the gallon and carries 4 people in comfort.  Wow! That's great.  But surely a 4.6 litre V8 that develops over 50% more horsepower will consume at least 50% more fuel... er actually no.

The official figures that Ford quote for the V8 are 25 highway and 17 city.  That's yanks for you, what we call "urban driving", they call "city".  Just goes to show, they think that they do things bigger!  That sounds bad, until you consider that this is based on the U.S. Gallon, not the Imperial Gallon. The Americans thought they'd have their own version of the Gallon, as ours was... too big for them.  They still have 8 pints, it's just that their pints have 16floz and ours have 20floz. 

Yes folks, the Imperial gallon is larger than a U.S. gallon.  Finally!  We have something that's bigger than theirs!  And the American mile is just the same as ours - to the inch (all 63,360 of them).

So what does this mean?  It means that their figure of 25 mpg is actually just over 30mpg when the conversion to Imperial is done.  To complicate matters, the U.S floz is bigger than a U.K. floz by a tiny percentage.  We've bypassed this little conundrum by comparing everything in litres.

Want to get mathematical?  OK, here we go.

    1 U.S. Gallon = 3.785411784 (X)  litres        1 Imperial Gallon = 4.54609 (Y) litres

Therefore to convert "miles per gallon" from U.S. to Imperial, multiply by Y over X.  Thus the "city" figure of 17 becomes an "urban" figure of 20.4.  The "highway" figure of 25 becomes 30.0; suddenly these figures make a lot more sense.

Hang on a minute!  These are manufacturers figures, not real world ones!  OK, that's true and your overall economy does depend on how you drive it.  My BMW gets a good stretch every now and then around the rev counter and still my economy is good, over 28 on average.  I regularly drive into London with hours in stop-start traffic, still I get over 28 mpg.

So, the end result is:  petrol consumption depends as much on the use of your right foot than what's under the bonnet.  If you want really great economy, buy a Toyota Prius.  If you want style, raw power and an adrenalin thrill every time you put your foot down - get a Mustang!

Summary : 4.0 V6 petrol will do 34 miles to the (Imperial) gallon in "extra urban"

A 4.6 V8 petrol will do 30.02 miles to the (Imperial) gallon in "extra urban", i.e. on the Motorway.

So... I should pack in the BMW and just drive a Mustang GT every day.  OK, I've convinced myself.  Now, where's that supercharger catalogue...
 

Check out the size, is it really another American "barge"? Of course it isn't.