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Old 08-08-2018   #31
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Quote Originally Posted by alexGS View Post
Any turbocharged engine is more efficient than a naturally-aspirated engine of the same capacity. Basic thermodynamics! The turbocharger or supercharger ensures volumetric efficiency (filling the cylinders completely) and this is particularly apparent when comparing our 1.4 Lounge with my 1.4 Abarth. Driving the Abarth so that the turbocharger is boosting only slightly, I can make the same trip as in the Lounge, but with one less litre used per 100km.

Andy made mention of supercar engines being efficient. I think thatís particularly hilarious. In the case of the Lamborghini Gallardoís non-Turbo 5L V10 (for example), itís extremely inefficient! Useful torque is produced over a narrow range from 4000 to 6000RPM - accessible when climbing a hill in 2nd gear, for example. At 2000RPM the engine struggles to pull the skin off a rice pudding, which equates to many driving conditions in 4th, 5th, and 6th gear - so it has to be kept Ďon the boilí in low gears. The only time it might be efficient is if cruising at 4000RPM in 6th - so 100mph+, in which it might use a similar amount of fuel to a Ďnormalí car travelling at 100mph. But with too many cylinders and poor volumetric efficiency, I wouldnít hold your breath. Overall average economy is in the region of 12mpg. I imagine driving an F1 car on the road would be broadly similar.

My Mercedes CLS had an even larger engine (5.5L V8) but was a lot more economical, 35mpg was achievable on trips and 26mpg as an overall average. Probably because it only had 392bhp and therefore excellent low-RPM torque. 100Nm was available at idle speed!

The reason the 500 with 1.2 is economical is, in my opinion, because it is tuned for a good spread of torque at 1500-3000RPM when engine and transmission frictional losses are low. The gearing exploits this torque to move the 900kg vehicle around easily at low speeds, even in high gears. The 69bhp allows for a top speed around 100mph. Attempting to cruise at 100mph would be difficult and inefficient.

The reason the Gallardo with 5.0 is uneconomical is, in my opinion, because it is tuned for the maximum possible power at 8400RPM when frictional losses are high. The gearing exploits this high RPM and is therefore less useful at moving the 1700kg vehicle around at low speeds. The 520bhp allows for a top speed around 200mph. Attempting to cruise at 100mph would be easy and relatively efficient.

Personally I feel thereís nothing wrong with the TwinAir apart from the ridiculous claims made for it. Similarly unrealistic claims were made for Alfa Romeoís 1.4 MultiAir.

-Alex
A turbocharged engine has the POTENTIAL to be more economical, it also has the potential to be far less efficient.
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Old 08-08-2018   #32
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Re: Why Twinair never really worked

Quote Originally Posted by alexGS View Post
Any turbocharged engine is more efficient than a naturally-aspirated engine of the same capacity. Basic thermodynamics! The turbocharger or supercharger ensures volumetric efficiency (filling the cylinders completely) and this is particularly apparent when comparing our 1.4 Lounge with my 1.4 Abarth. Driving the Abarth so that the turbocharger is boosting only slightly all the way, I can make the same trip as in the Lounge, but with one less litre used per 100km.

Andy made mention of supercar engines being efficient. I think thatís particularly hilarious. In the case of the Lamborghini Gallardoís non-Turbo 5L V10 (for example), itís extremely inefficient!

Super cars (generally) are more efficient at getting power out of the fuel they burn, thatís not to say they donít burn a whole oil tanker worth of fuel.

The best example I can think of is the Mercedes 6.3 (M156) which is you look on fuelly gets about 16ish MPG, however this engine has 7 times the capacity of the twin air, 4 times as many cylinders and 5 times the power output, however using the example above of 50mpg from a twinair which seems a fair average, the massive Mercedes engine is only using 3.125x as much fuel

On a like for like basis the huge gas guzzling Mercedes only uses a touch over 3 times as much fuel with 4 times as many cylinders to produce 5 times the power with 7 times the capacity.....

This is where super car engines are more efficient, itís not that the use less or little fuel itís that they get their power more efficiently from the fuel.

This comes down to the way they are tuned and designed to much higher standards and tolerances.

I believe the Gallardo gets a similar fuel economy and power output as the Mercedes but from a 5.2 litre engine.

Still over 5 times the capacity and 5 times as many cylinders and 5.5 times the Bhp.

The best analogy is Ďa sledge hammer to crack a nutí

Use a big enough hammer and the only effort required is to put the hammer on the nut, the weight will do the rest.

Start with a tiny hammer, not only do you need to lift it, you need a massive swing and a huge run up to get the same result. Fitting a turbo to a small engine is like adding a longer handle to the hammer, gives you more energy from your swing but you still require a little bit more effort to make the same swing.

If all you want to do is tap the nut gently, then a little tiny hammer (engine) is perfect, as you need barely any effort to lift the hammer to tap it. With the sledge hammer (Lamborghini) you still require a huge effort just to get it off the ground (keep the engine ticking over)

Hopefully that all makes sense itís very hot here and I think itís affecting my brain.
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Old 08-08-2018   #33
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Re: Why Twinair never really worked

Well, as some regulars will know, I'm now in a position to compare and contrast aTwinair (owned from 2011 to 2017) with a 1.2, which my wife bought 2 weeks ago. Early days with the 1.2, but it seems overall to return similar mpg to the TA, perhaps slightly better on a long a-road run.
Sold as an eco car, I have to agree that the TA and other small turbos don't really work. But if you want more performance, and the potential for good economy, they mostly do. Also, the TA's character is perfect for the 500, but a 3-cylinder would probably be more suited to power other cars such as the Tipo.
I was very impressed with a 1.0 turbo Astra I hired a couple of years ago, which seemed to pull at least as well as a N/A 1.6, but returned 50mpg.
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Old 08-08-2018   #34
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Re: Why Twinair never really worked

Quote Originally Posted by 306maxi View Post
Just to build on what you said, the twinair was sold as an eco engine, it isnít an eco engine.
Of all of the cars I owned since 1984, I registered each and every refuelling to calculate true mpg figures. Up to 2011 I saw relatively small car to car mpg differences. Of course later cars performed better, but normally this was only 1 or 2 mpg better than the previous car. In 2011 I bought my first 500 with TA. Then I saw someting that I hadn't seen before, a true trend break: This car was a whopping 10 mpg better than the previous car! Therefore my conclusion can only be that the TA is a true eco engine!
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Old 08-08-2018   #35
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Quote Originally Posted by AGH1965 View Post
Of all of the cars I owned since 1984, I registered each and every refuelling to calculate true mpg figures. Up to 2011 I saw relatively small car to car mpg differences. Of course later cars performed better, but normally this was only 1 or 2 mpg better than the previous car. In 2011 I bought my first 500 with TA. Then I saw someting that I hadn't seen before, a true trend break: This car was a whopping 10 mpg better than the previous car! Therefore my conclusion can only be that the TA is a true eco engine!
Exactly, my 3 series has one of those power meters on the idrive display. To travel along at 60mph uses only a tiny bit of power and torque and because itís got a high final drive, very few RPM are needed so itís stupid efficient.
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Old 08-08-2018   #36
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Quote Originally Posted by AGH1965 View Post
Of all of the cars I owned since 1984, I registered each and every refuelling to calculate true mpg figures. Up to 2011 I saw relatively small car to car mpg differences. Of course later cars performed better, but normally this was only 1 or 2 mpg better than the previous car. In 2011 I bought my first 500 with TA. Then I saw someting that I hadn't seen before, a true trend break: This car was a whopping 10 mpg better than the previous car! Therefore my conclusion can only be that the TA is a true eco engine!
what other cars were you driving before? Sounds like youíve been driving rather uneconomical cars in the past.
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Old 08-08-2018   #37
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Re: Why Twinair never really worked

Quote Originally Posted by 306maxi View Post
what other cars were you driving before? Sounds like youíve been driving rather uneconomical cars in the past.
Rather uneconomical? Rather normal would be more accurate in my opinion.

Before 2011 I drove: FIAT 128, Opel Corsa (twice), Peugeot 106 and 206. So all of these are small cars with not really powerful, naturally aspirated 4 cylinder petrol engines.
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Old 08-08-2018   #38
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Quote Originally Posted by AGH1965 View Post
Rather uneconomical? Rather normal would be more accurate in my opinion.

Before 2011 I drove: FIAT 128, Opel Corsa (twice), Peugeot 106 and 206. So all of these are small cars with not really powerful, naturally aspirated 4 cylinder petrol engines.
What engines are we talking about?

Just a car model name doesnít really say anything. Was it a Corsa VXR? That 3 cylinder Diesel one they did or the smallest petrol engine you could find?

Something with a small engine thatís overstressed is always going to return poor fuel economy, @jrkitching can testify to how much better the 1.2 Panda is on fuel than the 1.1.
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Old 08-08-2018   #39
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Re: Why Twinair never really worked

Quote Originally Posted by 306maxi View Post
Just a car model name doesnít really say anything.
The car model name would say enough if the TA would really be as terrible as you suggest. However: all petrol, never the smallest engine available, but nothing sporty either.

In my opinion the TA is the perfect example of an engine that is fully optimised for the legal test cycle (NEDC). There is nothing wrong with that. It results in lower official CO2 figures and therefore in lower taxes and lower pricing.
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Old 08-08-2018   #40
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Quote Originally Posted by AGH1965 View Post
The car model name would say enough if the TA would really be as terrible as you suggest. However: all petrol, never the smallest engine available, but nothing sporty either.

In my opinion the TA is the perfect example of an engine that is fully optimised for the legal test cycle (NEDC). There is nothing wrong with that. It results in lower official CO2 figures and therefore in lower taxes and lower pricing.
The survey says no unfortunately. The whole point of tests is to give people a good example of what their car will do in the real world, the Twinair is clearly a fail in this regard.
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Old 08-08-2018   #41
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Re: Why Twinair never really worked

Quote Originally Posted by 306maxi View Post
The survey says no unfortunately. The whole point of tests is to give people a good example of what their car will do in the real world, the Twinair is clearly a fail in this regard.
Note from that picture that the car with the least discrepancy between real world and test figures, is the biggest engine of the bunch.

Whatís also interesting is that the extra 20bhp difference between the 85hp and the 105hp twinair equated to less than 1mpg difference in fuel economy, which goes to show how much difference an optimised engine map can do despite the big increase in power.
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Old 08-08-2018   #42
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Re: Why Twinair never really worked

Quote Originally Posted by 306maxi View Post
The whole point of tests is to give people a good example of what their car will do in the real world
That is what unknowing people like to believe...

Looking in the survey, I see both the 1.2 and the TA105 reach 47.6 mpg in reality. The TA105 performs much better though. Therefore I would consider the 1.2 being the true fail here.
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Old 08-08-2018   #43
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Re: Why Twinair never really worked

Quote Originally Posted by AndyRKett View Post
the car with the least discrepancy between real world and test figures, is the biggest engine of the bunch.
Who cares about the discrepancy? I don't. The test results are just numbers that determine taxes. Nothing more, nothing less.
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Old 08-08-2018   #44
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Re: Why Twinair never really worked

Quote Originally Posted by AGH1965 View Post
That is what unknowing people like to believe...

Looking in the survey, I see both the 1.2 and the TA105 reach 47.6 mpg in reality. The TA105 performs much better though. Therefore I would consider the 1.2 being the true fail here.
The 1.2 is an ancient engine design that has been well developed over several decades.

The TA is an ultra-small ultra complicated engine with turbo and lots of clever and modern highly engineered technology, so to reach the same MPG figures in the real world as an ancient design, is the real fail, not only that but when the TA goes wrong, it goes really really wrong £thousand repair bills. The worse that goes wrong with the 1.2 is a head gasket which appears very infrequent on newer models and any garage can fix it with very little effort.

The TA is supposed to be a super-duper modern engine and extra economic and with next to no emissions yet in truth is manages to be equal too, what it is supposed to replace.

Your opinion is that the TA performs much better, but that is only conjecture, whereas the figures above, come from real-world testing of both cars side by side scientifically on the road.

Quote Originally Posted by AGH1965 View Post
Who cares about the discrepancy? I don't. The test results are just numbers that determine taxes. Nothing more, nothing less.
So if you had bought the much more expensive and complex TA over the 1.2 on the basis that it would be cheaper to run with better fuel economy, only to find out it was only 'as good' as the 1.2 and cost considerably more to repair and service, then I don't think you'd be quite so delusive.
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Old 08-08-2018   #45
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Re: Why Twinair never really worked

Quote Originally Posted by AndyRKett View Post
Note from that picture that the car with the least discrepancy between real world and test figures, is the biggest engine of the bunch.

What’s also interesting is that the extra 20bhp difference between the 85hp and the 105hp twinair equated to less than 1mpg difference in fuel economy, which goes to show how much difference an optimised engine map can do despite the big increase in power.
And I think this is the underlying truth, really... the 1.4 gives the most consistent economy, but is not the most economical. Over all of our 500 Lounge driving, we’ve averaged 6.1L/100 - the claimed figure is 6.2L/100 - so we are happy. It seems to work well in our driving conditions.

I’m still certain that the comments about supercar efficiency can be summarised as ‘not efficient in typical driving conditions’, otherwise they’d be turning in good mpg and low emissions too.

-Alex
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