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Author Topic: Fuel consumption  (Read 8098 times)
Lennart Sorth
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« on: October 30, 2006, 08:45:37 pm »

Since I had the 1.9i XU9JA (205 gti) engine put in  (courtesy of MatraMagic), it has always quite consistently done 11-11.5km/l (31 mpg), which I have found quite acceptable.

As you know, I recently had the engine rebuilt (long story) - and a local wizard finetuned the mixture adjustment,  and measured on a rolling road, where it delivered an impressive 136hp/206Nm

I have now done two complete tanks of unleaded 98.

The first full tank was spent doing "Christian Driving" - in James May style - as I wanted to see just HOW  far  I  could  push  the economy. In other words super-delicate acceleration, a lot of coasting in idle, etc - all the way down to slipstreaming trucks! - and the result was an impressive 13,1  km/l - ie 37 mpg!   - which really is very good indeed.

However, this is not what the car was made to do, so the next tankful, I decided to do a majority of "hair-on-fire" driving, with far more cold-start-short-trips (where I normally would mis-treat  my  Peugeot 106),  fast driving - still not breaking the speed limits of course, but many fullthrottle accelrerations - in other words, quite "inspired driving" to say the least, and this has resulted in 12.5 km/l    - ie 35mpg!

Having these two tankfulls back to back gives a trustworthy combined consumption which is simply astonishing.

I wonder how much hair I can still set on fire on that next tankfull ... Smiley
« Last Edit: October 31, 2006, 08:31:37 pm by Lennart Sorth » Logged

Lennart.Sorth@matrasport.dk
Murena 1983 1.9i silver // Alfa Romeo Giulietta 2.0d 2012 white // Smart 4two cdi 2010 blue //
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« Reply #1 on: October 30, 2006, 08:58:49 pm »

Sounds great! I have found can barely get 20mpg from my twin Dellorto setup.
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Anders Dinsen
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« Reply #2 on: October 30, 2006, 11:21:41 pm »

Sounds great! I have found can barely get 20mpg from my twin Dellorto setup.

That doesn't sound that bad, but tuning of the carbs with fresh gaskets may improve it somewhat, plus give you a more lively engine.
But the twin carb setup has never been designed for economy - it's performance it does, and particularly performance in the high revs!
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« Reply #3 on: October 31, 2006, 08:31:21 am »

I was impressed with my murenas fuel economy when i brought it home.
On the stretch from Esbjerg to Aalborg i recon it must have done at least 12km/l.
though I must admitt that the driving style was very "defensive" Smiley
Still... runnig twin Delorthos and a hot cam i find it very reasonable indeed....
But lets wait and see how it will do next summer  Grin
« Last Edit: October 31, 2006, 08:30:43 pm by Lennart Sorth » Logged
Will Falconer
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« Reply #4 on: October 31, 2006, 08:33:14 am »

A genuine 'S' on Solex 40's can get about 28mpg driven carefully but the Dellortos always seem very thirsty.

I think sometimes Dellorto 45's have been used and perhaps they dump more fuel into the engine than is necessary.

Of course Lennart's XU9 engine runs a standard Peugeot injection system which was designed to carefully meter the fuel being used subject to information that the various sensors give it. Tht's a very good result.
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« Reply #5 on: October 31, 2006, 08:55:28 am »

"a lot of coating in idle"

Assuming you mean coasting, isn't it better to coast with the engine in gear as the 1.9gti engine management runs a fuel injection over-run cut-off, so if you leave it in a high gear and remove your foot from the gas, it will use no fuel at all. Whereas if you let it idle, there will be some fuel used to maintain the idle speed.

Just a thought...
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Lennart Sorth
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« Reply #6 on: October 31, 2006, 08:40:09 pm »

isn't it better to coast with the engine in gear

haha - yes, I ment coasting and have fixed my typo - thanks. :-)

I'm not sure the LE2-Jetronic actually cuts off fuel alltogether, - it is a quite rudimentary system, without lambda sensor. But even if it does cut off fuel, I think the money saved on petrol would go into replacing the clutch some miles before it would otherwise had needed to.

/Lennart
« Last Edit: November 01, 2006, 11:26:04 pm by Lennart Sorth » Logged

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« Reply #7 on: November 02, 2006, 11:51:13 am »

isn't it better to coast with the engine in gear
I'm not sure the LE2-Jetronic actually cuts off fuel alltogether, - it is a quite rudimentary system, without lambda sensor. But even if it does cut off fuel, I think the money saved on petrol would go into replacing the clutch some miles before it would otherwise had needed to.

It probably does cut off fuel - it's not that primitive Wink though in your configuration it is optimized for performance, not economy and environment (which is why it doesn't have the lambda sensor and catalytic converter).

Besides, this should have no effect on the lasting of the clutch, as fuel cut off practically only happen when the clutch is fully released (i.e. in contact). But perhaps you meant something else?

- Anders
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« Reply #8 on: November 02, 2006, 04:03:21 pm »

It probably does cut off fuel
Yes I think you are right, - but the transition is a bit rough, so I have adopted a drivingstyle where I avoid it. Thats why I had forgotten :-)
When in a queue, doing 1000 rpm in fifth, and the queue slows down a little, I declutch, otherwise the transition from powered running, to fuel cut-off braking gives a shudder - not bigtime, but enough to make me want to save the clutch and transmission, - so I declutch by reflex.

There is however no shudder when using the engine more deliberately for braking (or maybe it is just masked at higher speeds/revs), - so its just when you are at almost-idle revs.  And yes, engine braking will also cause clutch wear, - don't expect me to be consistant :-)

only happen when the clutch is fully released
indeed, but even then it will cause wear, just as acceleration does.  Nitpicking maybe.


/Lennart
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« Reply #9 on: November 02, 2006, 10:35:04 pm »

It probably does cut off fuel
Yes I think you are right, - but the transition is a bit rough, so I have adopted a drivingstyle where I avoid it. Thats why I had forgotten :-)
When in a queue, doing 1000 rpm in fifth, and the queue slows down a little, I declutch, otherwise the transition from powered running, to fuel cut-off braking gives a shudder - not bigtime, but enough to make me want to save the clutch and transmission, - so I declutch by reflex.

I don't think it's the fuel cut off that you are feeling here, as it generally should not kick in when the engine is below 2000 rpm... meaning that your engine should receive a bit of fuel when you are running this slow. I just think it can't pull cleanly at that low rpm - I would suspect your flywheel is quite light, so that probably doesn't help either? Wink
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« Reply #10 on: November 02, 2006, 11:46:24 pm »

205 gtis are infamous for their jerky throttle at low revs. A remap or Superchip should cure it.
You should try my XS with a big Weber DGAS carb and wild cam at low revs - it is almost undriveable!
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Lennart Sorth
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« Reply #11 on: November 03, 2006, 12:17:23 am »

I just think it can't pull cleanly at that low rpm
nonono - it actually pulls incredibly cleanly and quite powerfull eg from 1000 in fifth.

Its only when you let go of the throttle to the point where the car starts to coast by its own inertia, rather than being propelled along by the engine, that I get that shudder. The slack in the gearbox/diff is being shifted around, and the car is now being slowed down by the engine.

The other way, - getting on the throttle again after having coasted a bit in gear, also requires a very gentle foot, and will never be totally smooth either - which is why I have taken to use the clutch during that transition.

In my Espace this is all taken care of by the Deep Thought ECU, and I never feel the transition at all - however, that car is almosty twice as heavy, so maybe it doesn't take much ECU magic to make it smoother.

PS: Macaroni: - yes, I know the 205's were known to jerky low revs/speeds - in fact I was driving along with a 1.9gti this morning, and noticed this. However, I think you need the Motronic ECU to be able to remap any chip. Thats at least what my rolling road tuning expert told me, and he should know, as he wrote his own software to chip all sorts of cars, but in particular the Peugeot gti's. Your XS sounds like a potential whiplash inducer in idle, but at the same time it must be a fantastic car :-)

/Lennart
« Last Edit: November 03, 2006, 12:20:52 am by Lennart Sorth » Logged

Lennart.Sorth@matrasport.dk
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« Reply #12 on: November 03, 2006, 08:42:43 am »

I just think it can't pull cleanly at that low rpm
nonono - it actually pulls incredibly cleanly and quite powerfull eg from 1000 in fifth.

Its only when you let go of the throttle to the point where the car starts to coast by its own inertia, rather than being propelled along by the engine, that I get that shudder. The slack in the gearbox/diff is being shifted around, and the car is now being slowed down by the engine.

Just a thought: It could also be the idle control starting to kick in? It shouldn't do that much around 1000 rpm, but the idle control (which is a so called PID controller implemented in the computer - for those of us who has studied control engineering Wink ) is activated as soon as you lift your foot from the throttle so depending on the mechanics/electronics/software involved, may start oscillate a bit when the idle isn't really an idling engine, but is actually loaded by the vehicle.
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Lennart Sorth
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« Reply #13 on: November 03, 2006, 06:38:09 pm »

It could also be the idle control
I guess you refer to the throttle switch, which is sensing when the throttle is back on its stop.

However, that slight shudder I refer to can also happen when the throttle is held away from its lower stop, if the car coasts faster by inertia than the throttleinput makes the engine run.

Anyway, - the conclusion is that the LE Jetronic probably does cut off fuel when I lift the throttle, and it could lead to improved fuel economy - at the minimal expense of maybe a bit more clutch wear.

However, if you are right about the 2000 rpm limit for the cut-off operation, then it will hardly ever happen on my daily commute to work, as I rarely get above 2000 (80km/h in fifth)  - more often I am trundling along just under 1000 rpm in fifth. In fact on the way to work today, I was pulling away from 800 (idle) ... still in fifth :-)
That was for the experiments sake of course, normally I would use the other gears as well - but it worked fine.

I also had a nice, free motorway ahead of me, when starting from a light crossing (I'm sure Anders can figure out where this is) ... and *boy* does that exhaust sound nice - all the way to an indicated 5200 rpm (which I know is more like 6000).  And when I eventually lifted the throttle, I DID save fuel on the suspiciously long way down to the  - ehm speedlimit. Ahem. :-)   

but as I said, I was all alone on that stretch of motorway.

/Lennart
« Last Edit: November 03, 2006, 07:58:02 pm by Lennart Sorth » Logged

Lennart.Sorth@matrasport.dk
Murena 1983 1.9i silver // Alfa Romeo Giulietta 2.0d 2012 white // Smart 4two cdi 2010 blue //
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