Could someone please explain to me how Ford state better mpg for the non tubo 3 cylinder than the turbo version.The turbo version is revving far less at the same speed

I assume it's just because the turbo is always going to allow more fuel to be burned. But I'm not sure, when you're just cruising shouldn't a modern turbo engine use no more fuel than the same engine without a turbo?

What figures are you looking at?

In the brochure they both have the same combined figure of 65.7 mpg

Auto catalog.com They say the non turbo 80bhp is doing 4000rpm in top gear at 80mph. but the 125bhp is only turning at 2890rpm due to its higher gearing at 80mph.As the 80bhp is revving far harder i would have thought the fuel consumption would be far higher.Also the cambelt on the 80bhp will have gone around millions of times more when it gets to its 150000mile change time ,if the 125bhp needs a belt change at the above mileage surely the 80bhp needs changing at a far shorter mileage.

It's not all about cruising, and mpg claims definitely won't be made at 80mph. The reason why the 125bhp makes 45bhp more than the 80bhp is because there is much more fuel being shoved into it at full throttle.

At say 60mph constant speed it doesn't always help to be revving at a much lower rpm as the longer gear means the engine has to work harder.

The 125bhp will have to be on boost to maintain the torque required to stay at that speed where as the 80bhp will probably be at a lower throttle position but with more rpm.

Quite simply put power costs money and more fuel. Cruising in general terms weaker engines do well but at different speeds to others but stopping and starting is a whole new ball game, powerful engines work less and should be better to an extent but the fuel tests in the Eu are done over a set of average speeds so you'll never really know what's better until both are tested by real humans.