Still not sure you really get it! Not that I doubt you hypermiling skills but I think anyone would be challenged in London! I am happy with my 40mpg and can get high 60s out of town. Trouble is the majority of my time is in town.

I've little doubt you've got it worse than me, but your tank average is 16mph, my commuters average 19mph (I said 20 before but that was lazy mental arithmetic). I actually leave after peak hour and normally get home before the afternoon peak or our averages would be surprisingly close. Just roughly it takes me 45 mins in the morning to travel 20km, that's 26km/h or 16.5mph for just the commute, my tank average speed bumps up a bit from the odd freeway run, but it's only by a couple mph.

I only see the slightest improvement in mpg on longer trips. With a petrol 5 speed you're burning more fuel than you need to at any speed above ~30mph.

UFI said:

My main secret to good economy across all my cars is high load/ low-moderate revs. Peak engine efficiency occurs just prior to enrichment.

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The problem is that the enrichment of small turbocharged petrol engines can already start between 50 and 75 % load. This is the main reason why many of these engines have a poor fuel economy in real life, although they perform very well in the NEDC. With such engines running high load at moderate revs is the worst you can do for fuel economy, since you will definitely run into the enrichment. Fortunately most cars with such engines have a gear shift indicator that warns you not to do this.

UFI said:

With a petrol 5 speed you're burning more fuel than you need to at any speed above ~30mph.

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Having driven our 1.6 16v Clio for many years up and down the country .......... we've had her since new in 2001 ............ going up the motorway at circa 70mph we consume maybe 40mpg, but when we come off the motorway and take it easy, the mpg'ness goes up circa 45mpg. We can do a steady 60mph and get 50mpg, but as the speed increases, the mpg goes down exponentially. Doing the same in the 85TA 500, the mpg is about 60mpg at a steady 60mph, and the same exponential thing happens as speed increases.

Round here, we average maybe 20mph or less, and we have hills! Loads of them! I mean it, HILLS.

Mpg seems to be in the low 30mpgs for the Clio over the years, but I've accurately logged 35.58mpg for the 85TA 500 over 7 fill-ups and 1,500miles.

We've only had the 85TA 500 a few short months, compared to the Clio of 14years.

Regards to all,
Mick.

UFI said:

I only see the slightest improvement in mpg on longer trips. With a petrol 5 speed you're burning more fuel than you need to at any speed above ~30mph.

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I'm sorry, but I don't agree that 5 speed boxes are less efficient. In fact a 6 speed will be less efficient given the same top gear ratio a 6 speed box will be between 3-5% less efficient.

But that's rarely the case, I've got a mix of 5 & 6 speeds, and generally can pull 5th gear in a 4 cyl petrol from 38km/h while a six speed needs something like 55km/h to get into top gear.

Even if you've got a close ratio six speed you're better able to keep the engine at peak efficiency with the extra ratios. There's a reason we're now seeing 9&10 speed automatics.

Both of these factors will override the small gearbox losses of an extra ratio. It only takes ~50W/h per km to spin the entire drive train of a FWD car at 40km/h.

AGH1965 said:

The problem is that the enrichment of small turbocharged petrol engines can already start between 50 and 75 % load. This is the main reason why many of these engines have a poor fuel economy in real life, although they perform very well in the NEDC. With such engines running high load at moderate revs is the worst you can do for fuel economy, since you will definitely run into the enrichment. Fortunately most cars with such engines have a gear shift indicator that warns you not to do this.

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I don't know about this. I've always used high load/ low revs and have always had one of the most economical TA's on here (and I still go for a play on the track or in the hills quite a bit). Where enrichment comes in isn't just dependent on load but RPM as well, ie less enrichment at lower revs. Some ECU's also factor in road speed, ie my Jeep 4.0 won't stray from 14.7 A/F unless it's doing over 90km/h.

UFI's shift indicator is happy with me running 100% load and it usually doesn't tell me to downshift. This is certainly something to investigate if I'm going to break 100mpg. I've got 8 months of warranty left then I can fit some proper hard wired instruments.

So anyway, did some testing today, the fuel trim data I was hoping to use seems to generate an almost random effect, so I tried the O2 sensors.

I wasn't driving (I was playing with the instruments), but there appears to be slight enrichment at around 1500-2500rpm (around where I drive) but it becomes quite a lot richer after that. I'll have to drive the car myself to find the sweetest spot regarding load and revs. Is it possible to do better at low load and higher revs? With no throttle plate load is less critical so it's possible.

UFI said:

So anyway, did some testing today, the fuel trim data I was hoping to use seems to generate an almost random effect, so I tried the O2 sensors.

I wasn't driving (I was playing with the instruments), but there appears to be slight enrichment at around 1500-2500rpm (around where I drive) but it becomes quite a lot richer after that. I'll have to drive the car myself to find the sweetest spot regarding load and revs. Is it possible to do better at low load and higher revs? With no throttle plate load is less critical so it's possible.

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I find my TA is a bit more economical at say 2300 rpm in 4th then 1800 in 5th. Bearing in mind peak torque is 1900 I guess anything under that is not going to be as efficient?

Please correct me if I'm wrong ............

Gentle driving results in better fuel consumption. The further you put the pedal down, the more fuel is consumed.

RPM is less important than pedal position.

Right or wrong?
If I'm wrong, why?

Mick.

Throttle position is largely irrelevant, all my OBD gauges can display throttle position but I've never found it to be of any use. IMO throttle position should be mostly ignored and Load should be considered in it's place. If you're at say 25% throttle, your load could be anywhere between zero (or close to it) and 100%.

Load x Rpm is what determines fuel use (this is how the MFD gives you an MPG read out), throttle opening is only relevant in that it's the mechanism to control load.

I'm very much a low Rpm/ high Load proponent, and I'd say most people who've delved into the topic are. Somewhat anecdotally, the Prius engine is restricted to 4000rpm and in motorsport if they want to save fuel they shift earlier but keep the accelerator to the floor.

In much the same way as drag on your car increases with the square of speed, so holds true for the moving parts of an ICE.

So, load is reference to torque, kind of, or at least use of torque (if that makes any sense). So does it not make sense to use the rev range that refers to maximum torque? I kind of get that but I can't get it out of my head that the harder an engine works the more fuel it is going to use (somewhat irrespective of how efficiently it happens to be working). Very much armchair physics but with an attempt to link it to common sense).

Mercky said:

I find my TA is a bit more economical at say 2300 rpm in 4th then 1800 in 5th. Bearing in mind peak torque is 1900 I guess anything under that is not going to be as efficient?

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BSFC charts tell us that peak efficiency will never occur above peak torque. What are you basing your observations on? Unfortunately the MFD is useless when trying to really fine tune driving style and OBD gauges are only very slightly better.

babyferrari said:

I kind of get that but I can't get it out of my head that the harder an engine works the more fuel it is going to use (somewhat irrespective of how efficiently it happens to be working).

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Load is the percentage of torque being produced for a given engine speed (in other words, at 100% load the engine is producing all the torque it can for that RPM - off idle that won't be very much).

It's true that as load increases, so does fuel use, but when I connected a device to count injector pulses to 2.3l four cylinder, I actually saw a noticeable dip in fuel use right at the expected BSFC (peak efficiency) window, it used more fuel both above and below that point.

I might see if I can connect this to UFI temporarily as it really would tell us a lot. We need some real world testing with some accurate instruments, the TA with Multiair won't necessarily behave like a more conventional engine would.

UFI said:

BSFC charts tell us that peak efficiency will never occur above peak torque. What are you basing your observations on? Unfortunately the MFD is useless when trying to really fine tune driving style and OBD gauges are only very slightly better.

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Just going by the mfd

On my last tank the MFD turned out to be 7mpg off As I head into the 60's that will only get worse. I don't understand why Fiat want to hide the fact that you're getting great MPG from you (Part of the problem is they use the same basic software from 500 to Ducato). By comparison Renault are spot on with theirs and are more accurate than the aftermarket stuff

UFI said:

On my last tank the MFD turned out to be 7mpg off As I head into the 60's that will only get worse. I don't understand why Fiat want to hide the fact that you're getting great MPG from you (Part of the problem is they use the same basic software from 500 to Ducato). By comparison Renault are spot on with theirs and are more accurate than the aftermarket stuff

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Lol! Welcome to the real world of TA mpg figures. You might want to consider doing yourself a massive favour, stop worrying about driving in the most economical fashion possible and start actually enjoying the car. I appreciate you are taking the whole thing very seriously and it clearly means a great deal to you, but if I spent ever driving hour worrying about how much mpg I'm getting or what peak torque is being produced or any such thing, I'd fall asleep in utter boredom! :devil:

Still UFI I have great respect for you....enjoy! it's what makes us all different and keeps the world turning!

Funnily enough I have always said I don't give a stuff about the mpg but more about the gpm. But I still find it an interesting topic!

I'm half way in this.
I like not worrying about the fuel, but because the info is there on the dash board, it's interesting to see if you can maximise the fuel economy.

We've had the Clio for nearly 14years and that shows MPG, and when rolling along up the motorway, it focuses your mind on fuel consumption. It has actually slowed me down over the years.

Back in the day when I was commuting from Cornwall to Glasgow once a fortnight in our Peugeot 205 diesel, I would leave here at 9ish in the evening and do a steady 80mph all the way on a full tank - 500miles - got to my digs around 3am. It had a big 50Ltr tank, thank goodness. That is 11 imperial gallons, so at a steady 80, the car was doing at least 45mpg.

No instrumentation/computer, just a fuel gauge and a speedo.

If I were doing the same journey at the same speed in a 500TA, I doubt I could get there without refueling ............ even if the 500 had a nice big 50Ltr tank as 45mpg at a steady 80mph is rather uneconomical.

Thank you UFI, I'm very interested in your findings and knowledge. Very interested indeed.

Regards,
Mick.

UFI said:

On my last tank the MFD turned out to be 7mpg off

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It's very hard to fill your tank everytime exactly to the same level, but if you don't do that, the calculated MPGs will be off. Therefore it's much better to calculate the MPGs over several consecutive tanks. I myself always use the same pump of the same gas station and park my car always exactly the same way next to the pump and always stop filling the tank the same way. Only with this procedure I find a persistent offset of the MFD of approximately 0.2 l/100km. So in my opinion the MFD of the 500 isn't useless at all.