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Discussion Starter #1
Yesterday I took a trip to the coast in our Ford focus.

This is a 250 mile round trip from here on mixed roads and I just wanted to share my findings.

On the trip our 1.6 litre Focus averaged around 35mpg driven in a slightly spirited fashion.

The last time I went on the same route I used my 2.3 litre Golf. The fuel consumption was pretty much the same at 34MPG.

Are we being told lies that larger engines always use more fuel? The Golf is meant to do about 30mpg, the Focus 40mpg.

Both cars are a similar size and weight, and according to the laws of physics shouldn't it take the same amount of energy to move and accelerate an object at a certain speed? (Give or take a small amount of rolling resistance, aerodynamics etc)

What do we all think about this?
 

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I've found that a bigger engine doesn't automatically mean worse fuel consumption. I know from many years of Sierra ownership that, in the real world, 2.0 ones use less fuel than 1.8s. I also know that on the motorway my 2.0 turbo Saab uses way less fuel than the 1.8 litre Volvo. However, around town its fuel consumption is absolutely dismal and much worse than the S40. Big heavy small-engined cars are generally crap on fuel. It may well be really economical at a steady 56 but in a world with hills and stop-start traffic, you won't get near what the book says it'll do.

In the context of your Focus, I've never found them to be massively underpowered but a 1.6 is possibly slightly too small an engine. However it's sweeter and revs better than the 1.8 so makes up for it, but you pay the price for working it harder at the pumps.

On the physics bit, yes but the question is of how much fuel the car has to burn to produce that amount of energy. Another example: on the motorway at a steady 70 my old Primera GT would do 37-38mpg quite easily. My 156 with the same weight, same size engine and the same power would struggle to get above 32-33.
 

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Discussion Starter #3
I am thinking that a larger engine generally has worse thermal efficiency, but then that would depend on the design of the engine.

I cannot make my mind up on whether the Focus is underpowered or has too tall gearing. At 70mph in 5th gear it will really struggle with any sort of incline unless you drop a cog or two and rev it. But at 70mph in top gear it is doing around 2800 rpm (About the same as my much more torquey Golf)
 

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No one has yet mentioned gearing, my guess is that the gear ratios will have more effect than the simple energy required to move argument.

Think about driving 10 miles in 2nd gear and 10 miles in 4th
 

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No one has yet mentioned gearing, my guess is that the gear ratios will have more effect than the simple energy required to move argument.

Think about driving 10 miles in 2nd gear and 10 miles in 4th
In Symon's case, the gearing compounds the issue because 5th is slightly too tall for the engine to pull cleanly on any sort of incline. You need to either drop into 4th or bury your foot in the carpet. Vauxhall used to equip Cavaliers and Vectras with similarly tall gearing with similar results.
 

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Discussion Starter #6
No one has yet mentioned gearing, my guess is that the gear ratios will have more effect than the simple energy required to move argument.

Think about driving 10 miles in 2nd gear and 10 miles in 4th
I think gearing does affect things to a degree, but only in the extremes.

My 145 QV had shorter overall gearing to my 2.0 156, yet the 145 was better on fuel slightly.

I would think that If the engine is running excessively fast for a given speed it will be wasting more energy as heat than it needs to.
 

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I was quite chuffed to get just under 28mpg from my Gtv on the way back from Scotland last week. 380 miles on one tank is almost a record, and not bad considering i was doing 90mph from Glasgow most of the way back to Lancashire :)
 

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Discussion Starter #8
That is pretty good Gaz. My old GTV was raely average more than about 22mpg.

On the same run as I did in the focus yeasterday I have managed 38 MPG in my BMW 528 and 36 MPG in my Fiat Coupe.
 

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Yeah the subsequent tank of mainly town driving was gone in 210 miles and 19mpg :cry:
 

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My newest car, the 6 cylinder gets 33 mpg.(8.5 litres perkm since new 20,700km) That is combined hwy and city driving.
40 mpg on the hwy and sometimes better. It loves the freeway!!
Auto box with 7 speeds.

Apparently this car appeals to women ;)

My Spider gets 10litres/100km, standard. 28mpg combined. 4cylinder and lighter than my merc., but older technology.
 

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Yesterday I took a trip to the coast in our Ford focus.

This is a 250 mile round trip from here on mixed roads and I just wanted to share my findings.

On the trip our 1.6 litre Focus averaged around 35mpg driven in a slightly spirited fashion.

The last time I went on the same route I used my 2.3 litre Golf. The fuel consumption was pretty much the same at 34MPG.

Are we being told lies that larger engines always use more fuel? The Golf is meant to do about 30mpg, the Focus 40mpg.

Both cars are a similar size and weight, and according to the laws of physics shouldn't it take the same amount of energy to move and accelerate an object at a certain speed? (Give or take a small amount of rolling resistance, aerodynamics etc)

What do we all think about this?
I imagine that if you did the same route in both cars driving like a granny you'd probably get 38mpg in the Golf and 44mpg in the focus
 

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My dad always used to say, a 1300 Cortina MKIII on a motorway doing 70 would have to work so much harder than his 2.0 OHC. Certainly a logic to it as KB suggested above especially taking into the gear ratios.

I only ever get about 45-48 mpg on a decent run in my tractored rattley old spanner box dieseased GT whereas my Ex missus in her 2010/11 2.0 MX5 reckons on a recent business trip the trip puter read 48. She sticks to 65 but even given the error on trip computers I reckon its a good 42-44.

Outside temperature and traffic, so many different variables.
 

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We're assuming both cars are in equally sound condition and are have equally efficient engines.

Focus 1.6 is a an older engine with mapping/pollution control that is maybe 10 years older than the Golf.

And it could have less sophisticated fuel metering and ignition than the Golf... the equivalent of running with a dodgy thermostat etc.



Ralf S.
 

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Discussion Starter #14
We're assuming both cars are in equally sound condition and are have equally efficient engines.

Focus 1.6 is a an older engine with mapping/pollution control that is maybe 10 years older than the Golf.

And it could have less sophisticated fuel metering and ignition than the Golf... the equivalent of running with a dodgy thermostat etc.



Ralf S.
I would have thought that the engine would have been a similar age design wise as both cars came out at a similar time?

The are both CF4 compliant as far as I know, although the Focus does have a throttle cable where as the Golf doesn't.

I think it is just due to the fact that the Focus needs working harder to make any sort of progress.
 
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