Miles per gallon

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tom
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Post by tom » Tue Feb 06, 2007 9:10 pm

The hydraulic pump makes less difference than you'd think, it is only loaded when the wheels are steering or if the accumulator is being recharged. The figures are by no means poor by comparison with other vehicles of similar weight and horsepower although leaner burn engines have come a long way since Simca designed the XU engine. Computer controlled ignition has helped a lot and fuel injection is far more refined. Carburetted engines are thirsty. Worn carburetted engines with worn carburettors very much worse.
The Turbodiesel BX estate is between 10 and 20% more frugal than a current Golf 1.9TD
at a steady 80 MPH!
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Post by Doz » Tue Feb 06, 2007 10:11 pm

Eric Brough wrote:I'm running a BX16 TXi - the late monopoint injection system. Over the last 20000 miles I've averaged 432 miles-per-filling. That comes out at 37.7 mpg.
E.
Now thats more like my old 16RS... I've found my strobe , so I'll tackle the thing tomorrow... I have thought about tracking down the bits and bobs and adding monopoint injection on and getting shot of the carb altogether ... I did it to my sisters Pug 205XS years ago....
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Way2go
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Post by Way2go » Wed Feb 07, 2007 2:46 am

tom wrote:The hydraulic pump makes less difference than you'd think, it is only loaded when the wheels are steering or if the accumulator is being recharged. The figures are by no means poor by comparison with other vehicles of similar weight and horsepower although leaner burn engines have come a long way since Simca designed the XU engine. Computer controlled ignition has helped a lot and fuel injection is far more refined. Carburetted engines are thirsty. Worn carburetted engines with worn carburettors very much worse.
This is a good answer regarding the pump, but why for example when the GTi is injected and controlled by ecu does it not achieve much better than 30mpg even when being driven calmly in a controlled manner?
Offhand I don't know what the mpg figures for a 2.0l Ford Mondeo are but I suspect much higher and it's a heavier car. :?
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pindimar
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MPG in petrol BX19

Post by pindimar » Wed Feb 07, 2007 7:09 am

well, my BX19 TZi manual wagon gets around 28 mpg or 9.81 litres/ per hundred kilometres on a country/city cycle, but around town it drops down to 24-25 mpg or 11.33 litres / per 100 kms. Total freeway & country running seems to be around 35-38 mpg.

How accurate my checks are is another matter, I guess??

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sleepy0905
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Post by sleepy0905 » Wed Feb 07, 2007 8:40 pm

well I am getting 37MPG out of my little petrol Whoo what a big difference :lol: :lol: It beats 16-17MPG from my previous car.
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Post by DavidRutherford » Thu Feb 08, 2007 10:12 am

Way2go wrote:when the GTi is injected and controlled by ecu does it not achieve much better than 30mpg even when being driven calmly in a controlled manner?
Fuel injection varies massively. One electronic injection system can be so different to another that there is no comparison.

For instance.... is the system single point, multi-point-paralell or multi-point-sequential. Airflow sensor... flap-type or hot-wire-type?

etc.etc.etc.

The BX fuel injection system (as I understand) is not massively advanced, as it uses a fair bit of analogue electronics to modify a basic fuel curve from a look-up-table. This is fairly crude, and not much more advanced than a carburettor (although far less likely to wear out)

As processor speeds have increased, modern fuel injection systems have become fully digital, and as such can be far more tightly controlled.

The same is true of ignition timing. Early electronic systems used little more than a MAP sensor and rpm speed sensor, and were analogue. The ignition scatter was large, and hence the engine could never run with optimum advance all the time.

Modern systems are far more advanced than this, with the same ECU controlling ignition and fuelling with fully digital control, and as such the engine can be on the limit of advance and the limit of lean-ness all the time.

Given that Electronic control has now advanced to the point that the processor is faster than the engine speed, I doubt that we will see the same advances in engine efficiency over the next 20 years that we have seen over the last.
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Post by docchevron » Thu Feb 08, 2007 11:58 am

..that_

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Post by Way2go » Thu Feb 08, 2007 1:29 pm

Excellent answer David! :D :D :D

Mine is the Motronic multipoint parallel. But of course injection is pre inlet valves so additional benefits on later engines will also probably advance through 2 stages 1) increasing from 2 to 4 valves per cylinder and 2) direct metered injection.

Presumably it's 'cos Doc's car has 16 valves he was able to reach his staggering 42mpg on that occasion. =D> I think that will never be attainable in my 8v auto. :cry:
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Post by tim leech » Thu Feb 08, 2007 1:46 pm

If yo work out how much modern cars weight compared to a car from the 80s its amazing.

This is down to ompuers and most fo all sfaety features Useing a mid range Golf as a reference, a 1.9TDI has approx 105bhp but weights 1400kgs where a BX 1.7TD has 90bhp but weights approx 1000kgs. So the BX has 15bhp per tonne more. So will be faster and more economical.

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Post by Philip Chidlow » Thu Feb 08, 2007 1:48 pm

Power to Weight ratios - interesting.

What's a 16v compared to a BMW 320 I wonder... and so on!
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Post by tim leech » Thu Feb 08, 2007 1:56 pm

Alot faster Phil! If you think that a standard D6C 16v is bang on a 1000kgs iirc and it has 160bhp thats 160bhp per tonne, depending which age 320 you have the range from about 150-175bhp and thats a big heavy straight 6 lump up front so I would imagine they weight about 1300-1400kgs.

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Post by tom » Thu Feb 08, 2007 8:44 pm

As David points out, much is due to the way the injection system is metred. K-jetronic was once considered very efficient but it ran on the principle of four injectors spraying fuel constantly. Multipoint is better as a rule but the Motronic system is controlled by an air mass meter which is very sensitive to leaky pipes of which there can be many on a GTI/TZI.
To get a real world figure, look at Doc's 16V which is well rebuilt. 42 is very good but it will drop a long way used hard. The average GTI is strangled by its cat and usually has a worn distributor plus big carbon buildups on the inlet valves, all of which causes its efficiency to plummet.
A good decoke can work wonders on them.
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tim leech

Post by tim leech » Thu Feb 08, 2007 9:34 pm

Tom do you rate any of these decokers you can put in your tank? I dont want to take my head off my 16v.

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docchevron
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Post by docchevron » Thu Feb 08, 2007 9:38 pm

The best way to de-coke a valver is give it a Billy special tune up.
Warm it up fully, then lots of high revs and over-run from high revs, clears an amazing amount of rubbish out.

Taking the head off aint too hard to do, but, use the engine as it was intended now and again and it'll keep itself in pretty good nick.

Of course, decent fuel helps too..

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Post by ken newbold » Thu Feb 08, 2007 10:00 pm

Philip chidlow wrote:I'm getting low to mid forties around town with the TXD and I would have expected better - I'm not driving it hard but there is a fair amount of stop/start and sub 5 mile trips.

Best on a trip was 52 mpg. Doesn't sound right to me - with all these stories of people getting 58 to 60 mpg out of theirs
Best I could get out of a n/a 19D Estate was about 55. I found my TZD estate would do quite a bit better.