Conference terri::cars_uk

    	Well, sound's about what I'd expect from a 16V under the conditions
    you descripe but I don't know how it's equivalents do...

    Yep, I don't know waht your reference is but the fuel economy on the
    hot hatches is not that good.
    However if you take the performance into the picture relatively it is
    VERY nice!
    
    Also you will find that once you've become adjusted to this type of car
    the economy will improve 10-25%.
    30-35 mpg is however representative.
    
    Peter

I currently drive a R5 Turbo - Fuel consumption goes something like -
30MPG around town - Driving car like a Go Cart
34MPG "         " - Driving car like the Vicar would 

37MPG M25 - M4    - Driving at 85 - 90 MPH
42MPG M25 - M4    - Driving at 70 MPH , without Turbo kicking in .

Yes I know the R5 is only a 1400cc car and all that , I also have driven a 
2000cc Injection Cavalier, and I got about 40MPG on a run .

Is it the 16V that kills the fuel , like the Turbo does on R5 ?

                        KR

         
>    I currently drive a R5 Turbo - Fuel consumption goes something like -
>    30MPG around town - Driving car like a Go Cart
>    34MPG "         " - Driving car like the Vicar would
>
>    37MPG M25 - M4    - Driving at 85 - 90 MPH
>    42MPG M25 - M4    - Driving at 70 MPH , without Turbo kicking in .
    
    Corr ... I've got an R5 Turbo too, and I don't get anything like that
    kind of economy.  If I remember right, its got a 9.5 gallon tank. 
    Around town I get on average 220 miles/tank, 23.15 mpg  and on a long
    haul, the most I've ever got out of the tank is about 290 miles, 30.5
    mpg, and at 85 -> 90mph I'd expect to get around 250 miles/tank, 26.3 mpg
    
    My around town is probably quite low as I live close to work and just
    about manage to get the choke off by the time I get there.   But, I have 
    other friends with R5 Turbos and their figures are very close to mine.
    
    Either you have one very exceptional car, or your turbo isn't doing as 
    much work as it should.
    
    .. John ..
    

    Actually, a Turbo makes it operate more economical as it delevers
    something for nothing: inlet pressure from energy out of exhaust gas.
    
    The problem in not the Turbo nor the 4 valve head. It's all about
    specific output: Kwatt/litre.
    To reach more power from the same volume one has two options:
    a. increase pressure
    b. increase revs
    Both will involve additional pumping losses and b. in friction losses.
    Also higher revs usally mean shorter stroke meaning more heat loss.
    All in all the higher the specific output the less economic the engine
    will get.
    
    As these models are performance packages the fuel/air ration is aimed
    at maximum energy and not maximum efficiency. Meaning a ratio closer to
    14 than to 16, meaning more fuel.
    
    Peter

    re .5
    
    A Turbo does not deliver something for nothing. The Turbo extracts
    power from the exhaust, but it is not at zero cost. The Turbo causes a
    higher pressure to exist in the exhuast manifold, which restricts the
    flow of the exhaust gas. This causes a small loss of power when you
    have a large volume of exhaust gas, as the piston has to work harder to
    drive the exhaust gas out of the cylinder.
    
    Also the Turbo engine has to have a lower than normal compression
    ratio, to compensate for the greater amount of fuel/air mixture being
    compressed in the cylinder during the compression stroke. This reduced
    compression ratio makes the engine less efficient than a similar sized
    non-Turbo engine during normal driving conditions.
    
    Andrew

    .6�    A Turbo does not deliver something for nothing. The Turbo extracts
    .6�    power from the exhaust, but it is not at zero cost. The Turbo causes a
    .6�    higher pressure to exist in the exhuast manifold, which restricts the
    
    It has a nice advantage: noise is much lower (because the energy goes
    into the turbine as you rightly point out). In terms of cost (and
    weight) a turbocharged engine requires a smaller muffler.

   >> Also higher revs usally mean shorter stroke meaning more heat loss.
    
    Really ?
    
    Does the con rod 'grow' with high revs ?
    
    Pete

    re .8
    
    The changing the length of the con rod won't change the stroke, although
    it will change the compression ratio. To change the stroke you need to
    change the crankshaft (and then the con rod to maintain compression
    ratio).
    
    I think .5 was suggesting that a higher rev design would use a shorter
    stroke (presumably to reduce the forces due to imperfect balancing).
    Quite why a shorter stroke means more heat loss I dont know.
    
    As for a richer mixture in a higher output engine. With good design the
    misture would be richer only when producing more power (I.e. full
    throttle). When at idle or cruise it should use the same mixture as the
    lower powered variant.
    
    Andrew

    A shorter stroke means a less ideal cumbustion chamber shape, resulting
    in more surface resulting in more radiation losses.
    Also a shorter stroke usually results in increased side forces on piston.
    
    An engine deseigned and tuned to deliver max. output at high revs WILL
    be less fuel efficient at lower revs/output.
    
    Obviously the engine consumes less when delivering 50 KWatt then when
    putting out 100 KWatt. However an engine to operate at 50 KWatt level 
    will be far more efficient when delivering this than an engine designed 
    to operate at 100 KWatt level.
    In other words a car designed for everyday use will be more efficient
    during evryday use then a car designed for high cruising speed or track
    racing.
    This daily fuel consumption however is no indication for the specific
    fuel economy for the engine in question, just for the design at that
    particular use.
    
    Peter

    42 mpg from a REnault 5 Turbo - NO WAY!
    
    I assume your working these out manually, whereas on the Renault 19
    your using the computer?
    
    My Renault 19 16v saloon averages about 29.2 mpg after 700 odd miles!
    
    Greg

    Fuel consumption depends a LOT on driving style.
    
    While in the US I had a car with a 2.2l Turbo engine. Most of the time
    I averaged around 31 mpg. That is US gallons, which means about 40mpg
    in UK gallons. This was for a heavier car, with bigger engine, with
    full US emission controls and using AC in the Summer.
    
    The key was that most of the time I (more or less) obeyed the speed
    limits. These are so low that the only time you need brakes are when
    coming to a stop. Virtually all bends can be taken at the speed limit
    in all weather conditions. So not only do you save energy by going
    slower, but also you save energy by not heating up the discs.
    
    At the end of 46000 miles the brake pads still had 70% unused. Only
    two tyres were replaced, because they got damaged.
    
    Andrew

    
    After 22K of R19 16v use the computer says:
    
    		38 at a steady 75
    		36 at          85
    
    		31 on short halls (2-6 miles 2*perday from cold)
    
    		27 when having fun. Well as much fun as you can have when
    		   the mid range punch is PATHETIC.
    
    When new these figures were a bit less. Note the CAT has a lot to do
    with more heavy fuel consumption, espesially when cold.
    
    P.S Get a RS2000 or CLIO, both handle well and accellerate better in
    mid range.
    
    

    
    
    During the period I ran my R5 GT Turbo, I tried a spell running the
    car "off the boost" and the difference in fuel consumption was quite
    dramatic, 42 mpg is pushing it a bit, but I'd say I got about 38-39
    mpg .... but zero fun factor !!!
    
    
    Graham

    These fuel computers readings are fun, but they're only 'instantaneous
    snap-shots' which are difficult to compare with overall averaging which
    is what most people (and the government figures) have to quote. (Yes I
    know they have an average readout, but how accurate is the fuel flow
    meter over high volumes??)
    
    So I'd prefer figures calculated from several, Tank to tank/ elapsed
    distance readings. 
    
    In my case I always reset my trip meter on fill ups and (less often
    now) calculate my consumption. My Rover 416 GSi (1600cc 16v single-cam
    multipoint EFi) gives around 33-35 mpg, If I have a particular thrash
    it can go down to 30-31. The best I've got is just over 35mpg.
    
    Now bear in mind this is the AVERAGE over a tank which is usually
    300 miles (sometimes more). In this distance I may have tip-toed around
    like a church mouse for several miles, then thashed it like whatsisname
    mansel for several other miles, so this I feel is a truer AVERAGE.  
    
    Richard

My Calibra 16v consistently gives the following averages on tank-to-tank measurement:

30-35 Plodding around towns
40-45 Light right foot, long run ave 70-75mph
30-35 long run ave 80-85 mph
25-30 SET DRIVER/MODE=LEADFOOT (>90mph)

But it's bl**dy boring driving 500 miles at 70mph (ave)

Clive

Taking a long term (> 2500 mile) average from the trip computer, a constant
34mpg is the norm.  A dash to Swindon from Reading comes out at around 29-30mpg.
42 mpg is the highest figure ever seen on the display, but that was at a 
constant 55mph on empty A class roads.

Terry

    Re: .15 �fuel computers... 'instantaneous snap-shots'
    
    On the R19 16v the mpg reading are not just snapshots, they are the
    average since the computer was reset.                          
    
    Roy (who has unexpectedly got a R19 16v on test for a few days)

    I get about 31 mpg in my Renault 21 Turbo which is not to bad for a 
    2 litre engine, As long as you don't drive like a man possesed its
    pretty good mpg.
    
    
                                 Steve.

    Roy, 
    
    What do you reckon to it then?
    
    
    Greg (missing the turbo)

    re:          <<< Note 2002.18 by KERNEL::SHELLEYR "Hypodeemic nerdle" >>>

    >>Re: .15 �fuel computers... 'instantaneous snap-shots'
    
>>    On the R19 16v the mpg reading are not just snapshots, they are the
>>    average since the computer was reset.                          
    
>>    Roy (who has unexpectedly got a R19 16v on test for a few days)

    Further along in my reply I also mentioned about the computer's
    average, and the accuracy of the transducers.
    
    However, I was referring more to the type of
    "at a constant 50 MPH I get xxMPG" These MUST be instantaneous
    snapshots, you couldn't possibly drive the car for an entire tankfull
    at EXACTLY 50 MPH, no more no less, no starting, no stopping etc.
    
    Now do you see what i'm getting at?. These figures are interesting,
    just as the governments 55 and 75 figures are interesting, but for the
    average car you need to know the OVERALL average over an extended
    period. 
    
    I think the miles/gallons is a more accurate indication, the filling
    pump must be accurate by law, and the amount you use over many fillings
    evens out 'brimming' inconsistencies, and your odometer must also be
    accurate by law. However the accuracy of the transducers (particularly
    the flow) used in these cars is not guaranteed (most motoring magazines
    use very expensive meters for their testing EVEN if a fuel computer is
    fitted).
    
    Richard