> Then don't buy a BMW. My '89 525i 2.5l averages 20-25 in town and a little
> better on the highway.

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>> Then don't buy a BMW. My '89 525i 2.5l averages 20-25 in town and a
>> little
[quoted text clipped - 3 lines]
> average over 30 (imperial) from my E36 328i and have had 40mpg on a long
> run with cruise control.
That's a typical US mileage for the M20 or M50 engine.
However, you and the OP are talking UK/Imperial, which he probably
didn't notice.
FloydR
For many years I drove an '84 e30 318i which I replaced with a '91 e30 318is
last year. I've driven the 16 valve engine long enough to be very sure that
it gets about 10% better mileage than the 8 valve engine. I've always
attributed the improved fuel economy to the updated fuel injection system on
the newer car because I couldn't think of any reason that more valves
should increase mileage. It's very clear that more valves should increase
the horsepower available from the same displacement but I can't think of any
reason for the increased mileage. These two cars and engines are very
nearly identical except for these two items. Anyone have an explanation or
similar experience to share??
>> Then don't buy a BMW. My '89 525i 2.5l averages 20-25 in town and a
>> little
[quoted text clipped - 7 lines]
> managing 45 with a light foot but I imagine the average is nearer 35.
> It's a heck of a powerful engine, most owners will rave about it :-)
Floyd Rogers - 28 Nov 2006 04:39 GMT
> For many years I drove an '84 e30 318i which I replaced with a '91 e30
> 318is last year. I've driven the 16 valve engine long enough to be very
[quoted text clipped - 6 lines]
> are very nearly identical except for these two items. Anyone have an
> explanation or similar experience to share??
There are so many things that affect fuel economy that the difference
between
a 2-valve and 4-valve engine is insignificant. For instance, the 4-valve
engine
makes more power, so that allows minor but very significant changes to the
rest of the drivetrain, like a lower numerical differential that allows
lower
rpm at cruise, revised gear ratios in the transmission. Don't forget that
a cleaner burn due to 4 valves allows the engine to run closer to
stoichometric
lean conditions.
It's true that the M50 engined cars had lower mileage than their earlier M20
brothers, but they put the gains into power and performance rather than
mileage.
FloydR
adder1969 - 28 Nov 2006 11:20 GMT
> For many years I drove an '84 e30 318i which I replaced with a '91 e30 318is
> last year. I've driven the 16 valve engine long enough to be very sure that
[quoted text clipped - 6 lines]
> nearly identical except for these two items. Anyone have an explanation or
> similar experience to share??
In general greater efficiency of the engine either results in greater
power and/or greater mileage althoguh one could argue whether a 16v
engine is always more efficient than an 8v one.
As far as advances in engine management goes, I get the same mileage
out of my '96 4.4 740 as my dad used to from his '86 2.0 Saab 900i
hsg@h-gee.co.uk - 29 Nov 2006 19:21 GMT
>For many years I drove an '84 e30 318i which I replaced with a '91 e30 318is
>last year. I've driven the 16 valve engine long enough to be very sure that
[quoted text clipped - 4 lines]
>the horsepower available from the same displacement but I can't think of any
>reason for the increased mileage.
You JUST said it - more power = less throttle for the same power as the 8 valve
engine therefore less fuel.
Power = fuel burnt More power = more fuel but if you don't use the more power
you use less fuel.
Boom Boom
Hugh
> These two cars and engines are very
>nearly identical except for these two items. Anyone have an explanation or
[quoted text clipped - 11 lines]
>> managing 45 with a light foot but I imagine the average is nearer 35.
>> It's a heck of a powerful engine, most owners will rave about it :-)
Sir Hugh of Bognor
The difference between men and boys is the price of their toys.
Intelligence is not knowing the answer but knowing where and how to find it!
Hugh Gundersen
hsg@h-gee.co.uk
Bognor Regis, W.Sussex, England, UK