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Technical Why Twinair never really worked

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Technical Why Twinair never really worked

306maxi said:
While yes, it is people’s fault somewhat, as the video shows, you end up with a lot of performance that you can’t use without burning a lot of fuel.
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Indeed, if you want power out you have to put the same amount of fuel in, the very act of burning the fuel has not yielded any significant improvements in the last 100 years, any gains have been modest at best.

With small engines most of he gains come from the engine being physically smaller hence less losses in number of moving parts and reduced friction.

These days the design of he cylinder can be carefully made on computer and the most efficient designs planned out before a piece of metal is cast, the next major leap would only come from a radical redesign of the internal combustion engine, or as the manufacturers are realising a switch to electric is far more efficient.
 
AndyRKett said:
Indeed, if you want power out you have to put the same amount of fuel in, the very act of burning the fuel has not yielded any significant improvements in the last 100 years, any gains have been modest at best.

With small engines most of he gains come from the engine being physically smaller hence less losses in number of moving parts and reduced friction.

These days the design of he cylinder can be carefully made on computer and the most efficient designs planned out before a piece of metal is cast, the next major leap would only come from a radical redesign of the internal combustion engine, or as the manufacturers are realising a switch to electric is far more efficient.
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Watch the video, you can actually get better economy by using a bigger engine that’s a bit less stressed as it doesn’t have to enrich the air to fuel mixture to prevent detonation as much in typical use cases.
 
306maxi said:
Watch the video, you can actually get better economy by using a bigger engine that’s a bit less stressed as it doesn’t have to enrich the air to fuel mixture to prevent detonation as much in typical use cases.
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But you then have frictional increases etc to overcome. The twin air if kept below boosting point should match or beat the 1.2 - but the gearing does not encourage this.

A small engine at 20% of performance will be better than a larger engine - but a smaller engine at 40% is likely to use more than a larger engine at 20%. Its down to the driver.

Their is still lots of way to improve petrol engines, variable compression springs to mind.

My xsr is capable of 55mpg if driven like a granny, but I can also manage 8 mpg if I am driving like a a loon.
 
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306maxi said:
Watch the video, you can actually get better economy by using a bigger engine that’s a bit less stressed as it doesn’t have to enrich the air to fuel mixture to prevent detonation as much in typical use cases.
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I did watch the video. With better engineering and more money spent you could overcome the problems such as pre-detonation and knock, when dealing. With small engine mass market cars it doesn’t make any commercial sense to chase these problems when the real goal is to get high figures from the standardised economy tests which are done at low loads in a controlled environment.

Essentially the small turbo engine is great for passing these tests but naff all use in terms of economy in the real world.

If you want a small engine with great economy and a turbo the best engine fiat have, (and have made for many years) is the 1.3 multijet one of their most robust engines and will easily get 60+ mpg all day every day no matter what you throw at it.


If there was any benefit to be had then I could see that they would try to fix the inherent problems, but given the looming electric revolution that’s going to happen in the next few years, the R&D money would be and is being spent elsewhere now.
 
AndyRKett; If you want a small engine with great economy and a turbo the best engine fiat have said:
Except short journeys on cold days, that engine chucked out no heat for at least 4 miles, too damn efficient for its own good.

Must point out I only managed 45mpg average with a best of 60 when I had it in my grande Punto. Sadly they discontinued the 6 speed just as I ordered.
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AndyRKett said:
Indeed, if you want power out you have to put the same amount of fuel in, the very act of burning the fuel has not yielded any significant improvements in the last 100 years, any gains have been modest at best.

With small engines most of he gains come from the engine being physically smaller hence less losses in number of moving parts and reduced friction.
Click to expand...


:yeahthat:


Reducing friction is the simplest way of gaining a modest improvement in efficiency. Fiat exploited this with the eco Panda in 2009 by moving to low rolling resistance tyres and thinner oil ; the two taken together were just enough to enable the car to make the 119g/km cut, allowing the car to just squeeze into what was then the £35 RFL band.
 
306maxi said:
Just to build on what you said, the twinair was sold as an eco engine, it isn’t an eco engine.
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That, in a nutshell, is perhaps the best single-sentence answer to the question posed in the thread title.

Although the real truth about this engine was out there soon after launch for anyone who took the trouble to research it, anyone buying it as an eco choice based solely on Fiat's marketing literature and published economy figures would, IMO, have a valid claim for misrepresentation.
 
Perhaps not an Eco engine as such but it's not exactly a guzzler either and considering the performance (relatively) it's pretty economical I think, currently over 50mpg on mine. There's not many petrol cars/engines that are as characterful and fun to drive that also achieve over 50mpg under normal urban conditions
 
Mercky said:
Perhaps not an Eco engine as such but it's not exactly a guzzler either and considering the performance (relatively) it's pretty economical I think, currently over 50mpg on mine.
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It’s no gas guzzler, you’re right, but that said it’s not really much better than cars built 20-30 years ago that are the same size.

The very old Citroen AX diesel built in the 1980’s could achieve 100mpg

A 1990s petrol fiesta could be eeked out to 50mpg.

The truth is that these cars are not really anymore economical than they where years ago, these days it’s their ability to pass emissions standards which is being sold to the general public as an improvement in economy.

All cars with an engine pollute, your average paying customer is not going to draw a distinction between 119kg/km versus 150kg/km of CO2, however tell them that they will get 5mpg more then they are more motivated to pick your car. Also by getting he CO2 figures down it changed the car tax bracket so again another reason to buy the car when really in the real world the car was no more economical than any other, in this case it is purely the engine technology used, helped the car look good on paper.
 
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 that’s particularly hilarious. In the case of the Lamborghini Gallardo’s non-Turbo 5L V10 (for example), it’s 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 ‘on the boil’ 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 ‘normal’ car travelling at 100mph. But with too many cylinders and poor volumetric efficiency, I wouldn’t 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 there’s nothing wrong with the TwinAir apart from the ridiculous claims made for it. Similarly unrealistic claims were made for Alfa Romeo’s 1.4 MultiAir.

-Alex
 
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alexGS said:
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 that’s particularly hilarious. In the case of the Lamborghini Gallardo’s non-Turbo 5L V10 (for example), it’s 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 ‘on the boil’ 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 ‘normal’ car travelling at 100mph. But with too many cylinders and poor volumetric efficiency, I wouldn’t 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 there’s nothing wrong with the TwinAir apart from the ridiculous claims made for it. Similarly unrealistic claims were made for Alfa Romeo’s 1.4 MultiAir.

-Alex
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A turbocharged engine has the POTENTIAL to be more economical, it also has the potential to be far less efficient.
 
alexGS said:
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 that’s particularly hilarious. In the case of the Lamborghini Gallardo’s non-Turbo 5L V10 (for example), it’s extremely inefficient!
Click to expand...


Super cars (generally) are more efficient at getting power out of the fuel they burn, that’s not to say they don’t 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, it’s not that the use less or little fuel it’s 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 ‘a sledge hammer to crack a nut’

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 it’s very hot here and I think it’s affecting my brain.
 
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.
 
306maxi said:
Just to build on what you said, the twinair was sold as an eco engine, it isn’t an eco engine.
Click to expand...

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!
 
AGH1965 said:
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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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 it’s got a high final drive, very few RPM are needed so it’s stupid efficient.
 
AGH1965 said:
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!
Click to expand...
what other cars were you driving before? Sounds like you’ve been driving rather uneconomical cars in the past.
 
306maxi said:
what other cars were you driving before? Sounds like you’ve been driving rather uneconomical cars in the past.
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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.
 
AGH1965 said:
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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What engines are we talking about?

Just a car model name doesn’t 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 that’s 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.
 
306maxi said:
Just a car model name doesn’t really say anything.
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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.
 
AGH1965 said:
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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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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