fuel consumption

[sambro]

driving normally,(not like a moron), whats the difference in fuel consumption, between a1.25 and a 1.4 ? or is it not worth worrying about?

[RWJ]

Dear Sambro,

So every car's fuel consumption is mesured in MPG (Miles Per Gallon). The higher the MPG the more economical your car is to run*. So different engines are more or less fuel effiencient than one another. There tends to be a correlation between the BHP (Break Horse Power) of a car and the engines overall fuel efficiency measure in MPG. for instance if your car has a 1.25 litre engine, with 60BHP the MPG measured on a combined cycle** (average with town and motorway driving) may be 47 MPG, whereas a slightly more powerful 1.4 litre engine with 80BHP may be slightly less fuel efficient and offer 42 MPG. So as a general tenant the larger and/or more powerful the engine the less fuel effiecient it will be.

*One needs to take into consideration though several other factors; engine size and fuel type. So whilst a 2.0 litre engine may return 25 MPG so may a 3.0 litre depending on how hard the manufacturer has worked to implement a fuel efficient engine and/or how much BHP either engines have (in some cases smaller engines on sportier cars have more BHP than those on larger engines). Consequently MPG is only an accurate measure of fuel economy 'relatively' speaking; clearly a 3.0 litre engine with the same MPG as a two litre will cost mroe to fill up as its petrol tank will be larger, however, with the same MPG figure, this just means that it will run for longer but cost more to fill up, but the difference between the cost to fill up and distance a tank can go will be exactly relative to a 2.0 litres. So secondly, it is important to note that diesel engines are more fuel efficient that petrol ones, so a 2.0 litre petrol engine with 150 BHP may return 30 MPG, and a 2.0 litre diesel engine with 150 BHP will likely return 43 MPG even though they are the same size an power.

I shall now continue in a second post as I have reached the word limit and have not yet fully answered the question

[RWJ]

**MPG is measured by manufacturers and delivered in 3 different figures 1. Combined MPG, as previously mentioned this is the average MPG of an engine if the car is driven over one trip both in town and on the motorway/dual carriageway/A-road etc. as such is a relatively *** good indication of how fuel efficient the car is in comparison to other cars, 2. Urban MPG, as you might expect this calculation is based on a car driving through town, and finally 3. Extra-urban MPG, driving on the motorway. Motorway driving will always (except maybe gridlock on the M25) be more fuel efficient than town driving, as one changes gear less using less petrol and keeps to a constant speed not accelerating a lot, roughly 60 mph which is the ideal speed for fuel efficiency.

*** It is important to note taht when manufacturers calculate the fuel efficiency of their engines they often suspend the car in mid air to 'simulate' it driving and so with no friction on the wheels their calculations are certainly fairly innacurate, so whenver you see a quoted MPG figure its usually wise to take a figure of 5 away from it to get a more accurate real-life figure.

So I hope the above has answered your question, I apologise if you already knew a lot of the technical details such as MPG and difference in fuel type, though its useful to know when deciding to purchase a car or not. Finally I refer you to either Top Gear Magazine or 'What Car?' the back pages contain extremely detailed layouts of each car model and engine in production today including MPG and occasionally even pence per mile calculations.

Have a great day

RWJ

[sambro]

excellent answer rwj