Small-turbo-engines don't deliver economy - now there is a surprise.

[Ausmartin1]

http://news.consumerreports.org/cars/2013/02/consumer-reports-finds-small-turbo-engines-dont-deliver-on-fuel-economy-claims.html

What I always suspected.... the chickens have come home to roost.

That won't be good for the Falcon 4 Cyl either I guess.....

[seedyrom]

Got to put some freeway miles on the wife's Ecoboost Mondeo.
Her around town avg. is 10.4 l/100.
Resetting the trip meter and driving back from Canberra on cruise control, the best I could get it to was 7.0 l/100.

I was expecting better quite frankly.

[IJ.]

No real surprise.. it takes xx amount of Fuel to produce yy HP to do zz Work... small engine+big car is never going to be a winner as you're still accelerating the mass from standstill (zz component)

[Jag530G]

The Cruze and Dart certainly justify having a smaller turbo 4. better performance for same (Cruze) or better (Dart) fuel economy. The BMW and F150 are pretty same same but the other comparions are different cars so hard to say.

Bear in mind the new CAFE requirements are based on EPA figures and small turbo engines certainly get better EPA numbers, hence CAFE numbers. Won't matter what the real world economy is. The industry is moving towards replacing 6 cylinders with 4s. Look at BMW, who are famous for their straight sixes. The only atmo 6s you get with BMW are the 125i and 325i. That's it.

If you have a look through the back of Wheels magazine, there are very few atmo 6 cyl sedans left. Hyundai have made mention that when they developed the i45 they delibrately chose to have only 4cyl and no V6 option is it lightened the design, not having to allow for the extra weight in the front end.

Cheers, Matthew

[Jag530G]

No real surprise.. it takes xx amount of Fuel to produce yy HP to do zz Work... small engine+big car is never going to be a winner as you're still accelerating the mass from standstill (zz component)

The key engineering point behind using a turbo is energy efficiency. A turbo partially recovers thermal energy lost in the exhaust, hence you don't need quite as much fuel to make the same power. An atmo engine simply wastes all the thermal energy in the exhaust. Also there is the issue of internal friction, a 4cyl has much less internal friction then a 6.

So far we are seeing turbo 4s replace 6s. Give it a few years and turbo 3s will replace atmo 4s.

Cheers, Matthew

[redvxr8clubby]

Got to put some freeway miles on the wife's Ecoboost Mondeo.
Her around town avg. is 10.4 l/100.
Resetting the trip meter and driving back from Canberra on cruise control, the best I could get it to was 7.0 l/100.

I was expecting better quite frankly.

7.0 l/100Km sounds OK to me, I have a Fiesta (1.6 petrol manual) and it does 7.0l/ 100Km, doesn't matter if it's highway, or peak hour Sydney it's that close to 7.0 l/ 100Km that it doesn't matter. I also have a 2.4 lancer wagon auto, it does more like 11 litres per 100 around town (don't use much for highway), VE SV6 auto, peak hour Sydney about 12.7 per/ 100, or about 8.5 on highway trip

[Woodchukka]

Mmmm. So a V8 stands to recover even more thermal energy with the addition of turbo chargers. Who thinks we can convince manufacturers V8 turbos as they stand to get greater gains in economy? :idea::lol:

[Jag530G]

Mmmm. So a V8 stands to recover even more thermal energy with the addition of turbo chargers. Who thinks we can convince manufacturers V8 turbos as they stand to get greater gains in economy? :idea::lol:

Already are. AMG are phasing out the 6.2L atmo and replacing it with a 5.5L twin turbo.
C63 AMG 6.2L V8 336KW 12.1L/100kms
E63 AMG 5.5L TTV8 386KW 10.0 L/100kms
more power less fuel, even in a bigger heavier car in this example.

BMW got rid of their old 5.0L V8 and replaced it with the twin turbo 4.4L V8. Better fuel economy and better emissions.

It's the way of the future.

Cheers, Matthew

[Xjas]

The key engineering point behind using a turbo is energy efficiency. A turbo partially recovers thermal energy lost in the exhaust, hence you don't need quite as much fuel to make the same power.

They do recover thermal energy but it is only effective when the engine is under sufficent load to produce boost, most of the time when you are crusing along at low loads they are nothing more than a exhaust restriction which I suppose would explain why they do well around town but are not much better than our N/A dinosaurs on the freeway.

[duke5700]

The Jetta I have gets into the 6's and the missus drives it around town in the 7-8s no worries. I thought that was ok for a 1450kg car with a little bit of go. It is no diesel miser, but its pretty good.

[whitels1ss]

I have an Audi TT for a runaround car it is great on fuel.
It goes around corners quite well also:yup:

[IJ.]

The key engineering point behind using a turbo is energy efficiency. A turbo partially recovers thermal energy lost in the exhaust, hence you don't need quite as much fuel to make the same power. An atmo engine simply wastes all the thermal energy in the exhaust. Also there is the issue of internal friction, a 4cyl has much less internal friction then a 6.

So far we are seeing turbo 4s replace 6s. Give it a few years and turbo 3s will replace atmo 4s.

Cheers, Matthew

Pardon?

It takes xx fuel/yy air to produce 100hp, only way it's going to use less fuel is if you run it at a leaner AF ratio.

Something like a Miller Cycle engine does this but in a conventional 4 stroke adding a turbo makes the smaller engine have the same output as a larger one but it still takes the same amount of power to move the same amount of mass.

All the turbo is doing is squeezing the 4.0L airmass into a 2.0L engine, it may have less parasitic drag with less cylinders and less overall mass due to the lighter engine.

[redvxr8clubby]

The key engineering point behind using a turbo is energy efficiency. A turbo partially recovers thermal energy lost in the exhaust, hence you don't need quite as much fuel to make the same power. An atmo engine simply wastes all the thermal energy in the exhaust. Also there is the issue of internal friction, a 4cyl has much less internal friction then a 6.

So far we are seeing turbo 4s replace 6s. Give it a few years and turbo 3s will replace atmo 4s.

Cheers, Matthew

Can't say I agree with the first paragraph, but with regards the turbo 3's replacing NA 4, I'm pretty sure Ford will be releasing a turbo 3 1.0 Fiesta early this year, I believe the turbo will be a premium price and an additional model, the 1.6 will continue to be available. If you look at the current small turbos replacing larger NA's they do seem to deliver better low to mid range torque and pretty good fuel consumption. VW Polo and Golf seem to be very good examples of this. It would be interesting to know what would be the manufacturing cost of a turbo 4 versus a NA six, or even a turbo 3, versus a NA 4.
Getting off the tubos for a moment, I was looking at a new Mazda six last weekend, can't help but notice they claim 6.6 l/ 100Km, the Fiesta is quoted at 6.1l/100km. Talking about claimed fuel consumption, would a Mazda 6 only use about .5l/ 100km more than a little Fiesta, I am sceptical.

[Jag530G]

Pardon?

It takes xx fuel/yy air to produce 100hp, only way it's going to use less fuel is if you run it at a leaner AF ratio.

Something like a Miller Cycle engine does this but in a conventional 4 stroke adding a turbo makes the smaller engine have the same output as a larger one but it still takes the same amount of power to move the same amount of mass.

All the turbo is doing is squeezing the 4.0L airmass into a 2.0L engine, it may have less parasitic drag with less cylinders and less overall mass due to the lighter engine.

The issue is the power lost in operating the engine to produce the 100hp NET power in your example. A turbo engine needs to make less GROSS power to make the same net power, hence less fuel is used.

Using your numbers, think of the energy needed for the intake and compression strokes of an atmo engine, that is 100% mechanical energy and thermal energy in the exhaust is wasted. In a turbo engine some of the otherwise wasted thermal energy is actually harnessed by the turbo for the same intake and compression, hence less mechanical energy is needed. That is where the better efficiency comes from.

Cheers, Matthew

[Ausmartin1]

The issue is the power lost in operating the engine to produce the 100hp NET power in your example. A turbo engine needs to make less GROSS power to make the same net power, hence less fuel is used.

Using your numbers, think of the energy needed for the intake and compression strokes of an atmo engine, that is 100% mechanical energy and thermal energy in the exhaust is wasted. In a turbo engine some of the otherwise wasted thermal energy is actually harnessed by the turbo for the same intake and compression, hence less mechanical energy is needed. That is where the better efficiency comes from.

Cheers, Matthew

Ok if that is the case (I'm not disputing EPA numbers) but in the real world it worse - where I guess drivers are driving them like their NA larger capacity engine ones.

Plus you have the Turbo lag, risk of shorter engine life (delicate for regular servicing) , potential turbo repairs/replacements..... So in the real world are the EPA figures real?
After all manufactures have been tweaking their models to get great government EPA results (with a detriment to eg. shift points in auto's etc.)

I realize all manufactures are heading down this path but don't expect the nirvana in the real world yet - unless you drive like miss daisy once you get your smaller turbo engine car.

Cheers,
Martin

[V28VX37]

I find the headline a bit misleading at a quick glance:

Consumer Reports finds small turbo engines don't deliver on fuel economy claims

You have to read right through the article to confirm that they talk about small turbo petrol engines. This is important because small capacity turbo diesels are a different story altogether.

My Monaro's all time average was 16.1 l/100km (5.7L V8, cammed, heads, 290rwkw)

The Skyline's all time average is 12.1 l/100km (2.5L I6, stock turbo, 200rwkw)

Dad's Toyota turbodiesel people mover back in Europe is always under 6 l/100km no matter what he does, towing a caravan included. It seats 7 people too.

This is real life fuel consumption data over the long term. I find it crazy that we talk about fuel 'economy' here with figures like 8 and 9 l/100km still being considered good. IMHO anything over 5l/100km for any normal use is not 'fuel economy', it's rubbish. Modded performance cars for enthusiast use are a excluded from this of course :)

[IJ.]

Interesting discussion guys, I came from 20+ years of smaller Turbo engines after starting out with larger V8's and while I can see and understand Matt's point like Martin in the real world it doesn't work that way :)

My Stock 240K km LS1 Adventra cruises not that far off my 3.0L Turbo cars L/100km and I'm sure with a freshen up and a tweak on the tune it can get much better, The Bigger engine in the Tonner is going to take some work but I think it too can return reasonable economy while having MUCH better driveabilty than the Turbo engine ever did!

[Jag530G]

http://www.epi-eng.com/piston_engine_technology/turbocharger_technology.htm

Here is a good scientific article on the physics behind turbocharger efficiency.

To Ausmartin. Trucks have long showed the reliability of turbochargers although I have some doubts about their longevity if subjected to irregular maintenence.

I suspect that twin turbo small capacity engines will work much better than single turbos because you could have one turbo set up to give boost at very low RPM, say highway cruising and the second turbo set up for mid range torque for accelerating around town.

I look at the CR report and don't see much of a problem when comparing like for like, sometimes same, sometimes better fuel economy/performance. I think if they threw in a few more examples, say TTV6 Mustang vs V8 atmo Mustang, the AMG's I mentioned, BMWs then I think the evidence will come out well in favour of turbos. The name of the game is meeting the new CAFE standards, so we can be a bit cynical about all this. CAFE will be based on EPA numbers so if the car makers game the EPA system yet deliver crappy real world numbers, they won't really care.

Cheers, Matthew

[redvxr8clubby]

The Jetta I have gets into the 6's and the missus drives it around town in the 7-8s no worries. I thought that was ok for a 1450kg car with a little bit of go. It is no diesel miser, but its pretty good.

Around town is quite variable also, I notice your location is ACT, I have driven around town in Canberra and it's nothing like around town in Sydney. I had a VX II LS1 Calais about 2 years ago. Around town in Sydney about 16.7 litres per 100km, around town when I was in Brisbane seemed to be in the high 11's. Once you get to end of the F3 and hit Pennant Hills Rd I am sure there is some mysterious force that sucks fuel out of LS1's.

[Party Pete]

The problem with turbo engines is they might gain some thermal efficiency from the turbo in some circumstances, but when you add boost you add intake heat reducing efficiency and increase compression meaning that fuel mixtures go up timing comes down to prevent detonation. The end result is that the wonderful on paper gains that come out in EPA tests (or ADR tests in Australia) normally don't translate into real world experience unless you are a real feather foot. Everyone is going the smaller engine with turbo route now not because it offers real advantages but because of the CAFE rules in the US which are based on the EPA figures. It won't actually reduce carbon dioxide emissions from cars in the real world, but since when do politicians worry about the real world when coming up with these rules.

For the record, I don't dislike turbo engines as such and accept that they can be very potent power plants, my comments are purely on this something for nothing marketing that is pushed about them at the moment.

[Pickles]

Well, the overall trend seems to be, smaller more fuel efficient engines, producing the same, if not more, power, by various means, including F/I.
Interesting to note though, that with the well publicized "Ecoboost" motor in the Falcon, said to give "almost" the same performance as the venerable 4.0L 6 cyl, that if one does try to emulate the 6 cyl's performance, yes the 2L turbo will "almost" do it, but in doing so, its fuel economy is very close to that of the 6 cyl!
Cheers, Pickles.

[IJ.]

Well, the overall trend seems to be, smaller more fuel efficient engines, producing the same, if not more, power, by various means, including F/I.
Interesting to note though, that with the well publicized "Ecoboost" motor in the Falcon, said to give "almost" the same performance as the venerable 4.0L 6 cyl, that if one does try to emulate the 6 cyl's performance, yes the 2L turbo will "almost" do it, but in doing so, its fuel economy is very close to that of the 6 cyl!Cheers, Pickles.

My point exactly, it takes fuel to make power to perform work, there are no magic engines ;)

Drive your modern well tuned/maintained V8 gently and they're surprisingly good, GEN3 has "Lean Cruise in the PCM it's just not enabled as it's a bit of an emissions nightmare If I freshen up the Adventra engine I'll have a play with it and see what happens.

[duke5700]

Around town is quite variable also, I notice your location is ACT, I have driven around town in Canberra and it's nothing like around town in Sydney. I had a VX II LS1 Calais about 2 years ago. Around town in Sydney about 16.7 litres per 100km, around town when I was in Brisbane seemed to be in the high 11's. Once you get to end of the F3 and hit Pennant Hills Rd I am sure there is some mysterious force that sucks fuel out of LS1's.

And people bag Canberra as being a horrible place to live.. good roads, no traffic, expensive living but can't have it all. Back on topic, even in Sydney the Jetta is pretty good. She has relo's there and we do spend a bit of time up there. The car doesn't seem to mind much at all, hwy is high 6's, around town 7-8s. My VX SS when it was stockish was mid 8's on the hwy with lean cruise @ 110kp/h and around Canberra 12.0 day in day out. Avg speed was 60km/h or so by the read out on the dash.


My point exactly, it takes fuel to make power to perform work, there are no magic engines ;)

Drive your modern well tuned/maintained V8 gently and they're surprisingly good, GEN3 has "Lean Cruise in the PCM it's just not enabled as it's a bit of an emissions nightmare If I freshen up the Adventra engine I'll have a play with it and see what happens.

It does require the same energy to move the same mass, that never changes, but with the newer technology they are trying to improve on the combustion process and make it more efficient, so it can take less fuel to give the same work when the current process is inefficient. The amount of energy that is currently wasted is quite large in the combustion chamber and this will be the point they are trying to improve on. You never know, they might move to the Brayton or Joule cycle as a powerplant for the car.

[duke5700]

http://www.brennanletkeman.com/blog/wp-content/uploads/2012/03/63-Chrysler-Turbine.jpg

[VYBerlinaV8]

A lot depends on how the car is driven and where. Lots of acceleration = lots of fuel used. Hills don't help either.

Living Canberra I found my stock VY would get mid 12s around town and high 8s to mid 9s on a trip. My 2011 WRX (also stock) gets about 9l/100km around town in Canberra.

Canberra is not a normal city, though, as it has stuff all hills and lots of 80-90km/h cruising even in peak hour.

[Jag530G]

^^^^^ The Bronze Blowtorch. Chrysler Turbine Car. Great stuff.

To IJ. Yes you need X KW to propel a car at Y velocity but the issue here is how much of the energy unleashed combusting a certain amount of fuel actually makes it to the flywheel. What you are talking about is X flywheel KW and yes that doesn't change but the amount of fuel needed to produce X flywheel KW has changed, much for the better. a VE2 3.0L 6 produces 190Kwand 290Nm and VL 3.0L 6 produces 114KW and 240Nm yet both get similar fuel consumption. Amount of fuel being used is roughly the same but the power is up by 67% and torque up by 21%. The torque increase is actually the interesting one, because torque is directly proportional to BMEP (Brake Mean Effective Pressure) in the combustion chamber. over the last 20 odd years engine designers have managed to get a 21% increase in BMEP for basically the same Specific Fuel Consumption. Also that increase BMEP is driven by higher compression ratio yet it is with the same fuel, 91 octane. A lot of it is due to improving computational fluid dynamics, designing the combustion chamber on computers to minimise pre-ignition and allow for the higher compression ratio.

Cheers, Matthew

[IJ.]

The weight of the VE is probably up by about the same percentage Matt ;)

[sv300 - 75]

some of the other things that have changed over the years is the actuall efficency of the engine.
by this i mean friction surfaces, mechanical loss, and combustion efficency (i call it the cannon ball effect)

i saw this in a doco about an F1 car.
if you imagine an old school cannon with a 100mm bore with 1kg of explosive.
if the cannon ball is 95mm in diameter the ball when fired might reach 300m in distance.
if the cannon ball is 99mm it might reach a distance of 450m.

there is less engergy missing the cannon ball so there is more energy pushing it out the cannon.

in an F1 car the gap between the piston and cylinder wall is soo tight that it cannot move when its cold.
the engine needs to be heated up with hot water before it can even start.
this tight tollerence means that they can get even more horsepower out of the same amount of fuel because its more efficent.

with better technology they have more accurate clearances in the engine making it more efficent.

a turbo engine helps with the air to fuel ratio but might not help with the efficency of the engine.

[Jag530G]

The weight of the VE is probably up by about the same percentage Matt ;)

Yes, which leads me to suspect the specific fuel consumption of the 3.0L HFV6 is actually better than the RB30E despite much more power and torque. In the previous post I was making a fuel consumption comparison based on the over all car's fuel consumption. A VE is heavier by about 450Kg, has a bigger frontal area but on the plus side has a better Cd (0.34 vs 0.45) and 6 speed auto vs 4 speed auto. Probably nearly balances out.

Something to bear in mind with these new "small capacity" turbo engines is that they run fairly low boost to keep the compression ratio up, which means less turbo lag and much less of a torque hole off boost. The name of the game is fattening the low(ish)-mid range torque curve (ie increasing the area on the curve) to match the low/mid range torque curve of a bigger capacity engine. Its not like the old high performance turbos with low comp ratios and big boost levels. I'm a great believer that the key to good city fuel economy is good low/mid range torque, everything else being equal.

On a side (but slightly related) note, I read recently that the new 6.2L LT1 produces more torque 0 - 4,000 rpm then the old 7.0L LS7. Some people are a bit critical of the fact that it is only 10Kw more than the HSV GTS spec LS3 but LT1's big fat torque curve ought to make a noticeable difference in real world driving and economy.

Cheers, Matthew