Diesel Payback

[Spencernj]

Originally Posted by Ace Demon

Err, quite.

I agree that modern normally aspirated petrol cars feel gutless. Too much weight and not enough cubes.

It also due to the fact that petrol engines (and particularly small ones) have got more and more over-square in recent years so they have a shorter stroke and wider pistons need to be reved more and produce more bhp at peak but less torque. I am not sure what the thinking behind this is but probably due to reasons of compactness and also that over-square engines have wider bores so have more room for more vales (i.e 16 valve engines) and bigger valves which are better for efficiency.

[seven7]

Originally Posted by Spencernj

It also due to the fact that petrol engines (and particularly small ones) have got more and more over-square in recent years so they have a shorter stroke and wider pistons need to be reved more and produce more bhp at peak but less torque.

Not a fact in all cases. Mr Fords engines were oversquare in the 60's the 1600 x-flow was 81 bore x 78 stroke approx but move to the late 90's and the Focus 2 litre petrol was 85 bore x 87 stroke approx. The 1600 petrol in the Ceed is 77 bore x 85 stroke, not oversquare by any stretch of the imagination..

[Ace Demon]

Originally Posted by Spencernj

It also due to the fact that petrol engines (and particularly small ones) have got more and more over-square in recent years so they have a shorter stroke and wider pistons need to be reved more and produce more bhp at peak but less torque. I am not sure what the thinking behind this is but probably due to reasons of compactness and also that over-square engines have wider bores so have more room for more vales (i.e 16 valve engines) and bigger valves which are better for efficiency.

More valves make better use of head area which allows bore to be reduced. Which is what has happened. Modern engines don't produce less torque. The issue is that cars have got about 30% heavier without a corresponding increase in engine capacity, hence no increase in torque (unless forced). That means more revs are required to get the same response.

[dubster]

Apologies, my last post on this thread was rather off topic, was just thinking aloud
To redeem myself, I've just excel'd last months' fuel usage in petrol, and compared to my current diesel's average on same journey.

Petrol: 1408 miles @ 37mpg (avg) @ 1.38/litre = £236 in fuel (24 sept - 24 oct)
Diesel: 1408 miles @ 46mpg (avg) @ 1.42/litre = £195 in fuel

That's a clear £40 cheaper in that month, £480 per year extrapolating that out!
Even just working out a single month, that completely tallies up with Seven7's figures

In case it's helpful, excel sums are:
Miles / MPG * cost per gallon

[seven7]

Dubster

Not only is the 46 mpg well short of the official urban its 27% short of the official combined of 62.6 mpg.

And people moan that Kia's perform badly compared to the official figures.

If I had my anorak handy I would read what they say on a Seat forum.

[dubster]

Yes indeed mate, it should manage better than 'urban mpg' on my 30 mile country lanes commute!