475HP 7L 3760lb Z/28 $36K - How do we get there?
#46
Camaro weighs more that one competitor direct competitor, of course it is interesting that you don't mention that it is lighter than the Challanger. While the Mustang is a key competitor GM will not sell 100,000 cars to would be Mustang buyers. Unlike guys like us most folks that buy a new car have no idea what it weighs. They care about overall performance and value which is where GM has spent their time and money. I would love to have a Camaro that weighs less than a 4cyl FWD car but that aint gonna happen. Also instead of the 328 why not look at the M3 or 335? Perhaps because they weigh about the same as the Camaro. There was a guy a few weeks ago who tried to use the Smart car as a basis of comparison.
SE 3720lbs
R/T 4041 lbs
SRT8 4170
The 335i coupe, BTW, weighs 3571 lbs. Is that the same as the Camaro? No. The M3, which is certainly in a different league here, weighs 3704 lbs. Does even the lowliest, most basic, V6 Camaro weigh that? Once again NO.
Also, 100,000 Camaros was the sales goal here.
If you're not bothered by the Camaro's weight - well that's fine. But don't try to spin a tale of inaccurate facts to justify it. That's just annoying.
Last edited by Z284ever; 10-12-2008 at 11:46 PM.
#47
But it does depend on how you've designed and tuned the engine. If you're just going for output and speed, certainly the mileage will go down. If you're trying to take advantage of the bsfc improvement (europe), you'll find turbo/super is an advantage.
Just think about it: if you spend an extra 20Hp to rotate a blower, you can get an extra 50+ in output. It's a net gain in efficiency.
But what you're talking about now is fuel consumed per displacement...which really doesn't tell you much. Of course a blown 6.2 is going to consume more fuel than a n/a 6.2 (or 7.0): the blown has much higher output and is burning much more fuel.
But that doesn't really tell you which is more efficient.
As a point of reference, I point you to the 1996 Mazda Millenia, where a supercharger was used for efficiency. With the s/c, they were able to get higher output with better fuel economy; i.e. better bsfc.
Last edited by blackflag; 10-13-2008 at 12:43 AM.
#48
I have to disagree. First of all, you can't quote one number for bsfc for an engine. bsfc changes across engine speed and engine load...and with valvetrain, and from engine to engine. So quoting one number is silly. On the contrary, bsfc improves with forced induction. Turbocharged or supercharged engines offer better fuel economy...or better bsfc...which is why they're used so frequently in europe.
BSFC is related to how much energy you can draw out from the same amount of FUEL, not DISPLACEMENT. Boost requires richer mixtures for the same hp levels a larger, but equal hp, engine requires. Why? because compressing air charge will ALWAYS increase the temperature of the charge, and reduce the knock resistance of the intake charge. Likewise, the higher compression temperatures will cause faster flame fronts, requiring less advance timing and more need to richen the mixture to avoid detonation. boost + lean = boom.
But it does depend on how you've designed and tuned the engine. If you're just going for output and speed, certainly the mileage will go down. If you're trying to take advantage of the bsfc improvement (europe), you'll find turbo/super is an advantage.
Yes, it is true that compressors of different sizes spool up at different rpms/air flow but those efficiency curves relate the thermal efficiency of compression... not how fuel efficient the turbo becomes. two different concepts.
Just think about it: if you spend an extra 20Hp to rotate a blower, you can get an extra 50+ in output. It's a net gain in efficiency.
The fact is that a 500hp blown engine (like the Terminator) needs more than 5#/h larger injectors to make the same hp numbers as a 500hp N/A engine... that should be a big tip off about fuel efficiency under load.
It's really not about little engines, as you can find tractor-trailers with turbos (where you want fuel economy), etc. But you're right...when comparing comparable power, the boosted engine can give the same output - with less displacement, less friction, less parasitic losses, etc. Therefore, lower bsfc.
But comparing similar displacements doesn't make sense. You're talking about bsfc - or how much fuel is consumed per horsepower. When you look at it that way - how much fuel you're burning per horsepower - for the same output, the boosted is burning less. More efficient.
As a point of reference, I point you to the 1996 Mazda Millenia, where a supercharger was used for efficiency. With the s/c, they were able to get higher output with better fuel economy; i.e. better bsfc.
Volumetric efficiency is NOT equal to BSFC (fuel efficiency).
Next week's lecture: Why boost is NOT equal to air-flow. Tune in early
#49
Nope, sorry, it just doesn't work that way.
BSFC is related to how much energy you can draw out from the same amount of FUEL, not DISPLACEMENT. Boost requires richer mixtures for the same hp levels a larger, but equal hp, engine requires. Why? because compressing air charge will ALWAYS increase the temperature of the charge, and reduce the knock resistance of the intake charge. Likewise, the higher compression temperatures will cause faster flame fronts, requiring less advance timing and more need to richen the mixture to avoid detonation. boost + lean = boom.
BSFC is related to how much energy you can draw out from the same amount of FUEL, not DISPLACEMENT. Boost requires richer mixtures for the same hp levels a larger, but equal hp, engine requires. Why? because compressing air charge will ALWAYS increase the temperature of the charge, and reduce the knock resistance of the intake charge. Likewise, the higher compression temperatures will cause faster flame fronts, requiring less advance timing and more need to richen the mixture to avoid detonation. boost + lean = boom.
In fact, if an automaker released any car that was running rich throughout the operating range, it would never, ever pass emissions.
Trust me, everything europe does is for better fuel economy. Everything.
How about this... for the same amount of air you can either use 90% VE with a 6.5L engine, or a 100%VE 5.9L engine, or a 130%VE 4.5L engine. Same air flow, and EVEN if you ignore the need to richen the boosted engine, or the incrased charge temps, you could get the same hp of combustion... BUT you lose hp that gets to the wheels since some is eaten up turning the blower, or backing up the exhaust.
Like my example pointed out - you can spend 20Hp driving the belt of a supercharger...or in output loss from turbo backpressure...but end up with a 50+ Hp net gain. More output, same displacement. Higher efficiency.
(And that also explains how you can get to 120% VE. Only with boosting. Higher efficiency.)
turbos on diesel engines are COMPLETELY different animals. why? because diesel has a VERY high resistance to knock, and the very mode of operation accounts for such an event. Diesel engines use turbos because there is untapped energy potential in the fuel that would not be tapped (and WASN'T) until you increase compression ratios. Pump gas? ~8.5 to 9 DCR. Diesel? 14DCR isn't uncommon. apples and oranges. If you plan on sticking with gasoline, running boost will NOT increase BSFC... it decreases it.
As I've said, the use of a blower is minimal at idle and essientially you have a N/A engine... a SMALLER N/A engine... which of course will produce less hp and consume less fuel than a larger N/A engine. Last time I checked, the EPA doesn't do milage testing at WOT, under boost.
Do they run at WOT? Unlcear, depends on the weight of the vehicle and size of the engine. There are some cars that have run the epa and have gone into wot. But that's irrelevant, because you don't have to be at wot to have boost. (For example, you could be at 3000rpm and 75% throttle and be in boost.)
But seriously...if you designed a turbocharged engine...then it failed to boost through a large portion of its operating cycle...you will have really screwed things up. It would be like driving a car with a small engine with a compression ratio of 8...it would be a disaster. In fact, you could simulate this if you wanted to. You could take a production turbo engine and put on a turbocharger that's twice as big as it should be. A turbo from a big truck. It would be way, way underpowered...and probably never boost until wot.
Fortunately, nobody does that. They do the opposite...and use turbos on the small side.
Again, as evidence of a boosted engine with greater fuel economy (greater efficiency)...look at the supercharged Millenia. Better fuel economy. And more output, too.
Same with the Solstice. Turbo gets better fuel economy. Same with dozens of applications across Europe.
#50
sigh... I'm not going to argue vauge opinions with you. There simply isn't any science to support your boost=better BSFC claim. It doesn't exist, it never has.
OVER 50% of all european sales in the past 2 years have been DIESEL. Much different issue... you NEED the boost to get full energy extraction from the high-knock resistant fuel... gasoline doesn't need that if you pick the right DCR.
Wow... its scarry to think you calibrated an engine.
1) stoich (14.7 pounds air:1 pound gasoline) is NOT the "ideal" for max hp generation. Running rich is required in nearly EVERY engine at WOT, in an attempt to prevent knock from creeping up. Why? because the most heat you can generate from gasoline would be with complete combustion at stocih mixtures.
Any leaner and you are just adding excess air which dilutes the combustion charge, reducing how much fuel enters the cylinder. (which is why hot EGR gases REDUCE exhaust gas temps).
Any richer and the hydrocarbons are incompletely combusted (CO emissions and even unburt HC emmissions climb, while the exhaust temperature drops due to less heat being released by combustion).
In a perfect thermodynamic view you would run at stoich for max hp at all times and limit the air and fuel that enters at each cycle. Unfortunately, the high temps generated from complete combustion climb proportionally with the amount of fuel being combusted in a given cylinder... part throttle leads to very low VE% (say 40% instead of 100 N/A or 130 boosted) and the amount of fuel in the cylinder is fine. At WOT, there is so much heat being generated in the same combustion space that tempertures spike fast as shown by NOx emissions spikes. EGR was used to reduce these temps and hense the effective VE/BSFC. Under boost the intake charge is even hotter and spikes to hotter temps which can melt pistons, tulip valves, and kill NOx emmisions.
As a result, even NA engines do NOT run stoich at WOT, or even 85% throttle... they run rich (~12:1 AFR) to reduce the temps while not sacrificing as much hp as if they ran lean to do the same thing (~17:1 would do it if you wanted to... but excess fuel drops to absorb heat is a safer bet).
Boosted engines? heat is an even bigger concern for safety reasons (and is why intercoolers, water injection, and nitrous can have such beneficial hp gains) and they have to go even RICHER than N/A... which INCREASES their BSFC, and why engine of similar max hp, and similar max rpm, need larger injectors in a boosted application.
This is not a new concept, it's been known for YEARS, and by millions of engineers and engine builders.
How can a "turbo engine" be more fuel efficient than a N/A engine?
1) smaller displacement - the HAS to happen. Even if there is no boost, the turbo/blower engine still has inherant power losses over an identically sized engine due to:
a) the decreased DCR nessesitated by the boost levels and in the case of a blower,
b) the hp losses (however minimal it may be when at or near idle... it's still there)
c) the extra weight of the engine/car due to turbo/blower/intercooler (100-200 pounds)
2) Test only at idle, cruise, and part throttle where stoich levels are maintained. Once you go WOT you will never be able to get the same hp out of a given amount of fuel as a NA engine for the need to be rich and power the power adder.
Boost Power Adders are designed to add power capacity, not increase efficiency. Volumetric efficiency? yes... but the extra heat requires adjustements which in the gasoline world involves going rich.
I dare you to show me even 1 boosted vehicle that runs stoich at WOT. If you do, it's got some serious extra weight in the heads, block, or intercooler. That's just the physics at play.
OVER 50% of all european sales in the past 2 years have been DIESEL. Much different issue... you NEED the boost to get full energy extraction from the high-knock resistant fuel... gasoline doesn't need that if you pick the right DCR.
Actually, boosted engines - when designed from the factory - operate at stoichiometric when not at wot. Stoich is how fuel burns, regardless of whether it's boosted or not. So boosted does not mean richer...and I know, because I've calibrated them.
1) stoich (14.7 pounds air:1 pound gasoline) is NOT the "ideal" for max hp generation. Running rich is required in nearly EVERY engine at WOT, in an attempt to prevent knock from creeping up. Why? because the most heat you can generate from gasoline would be with complete combustion at stocih mixtures.
Any leaner and you are just adding excess air which dilutes the combustion charge, reducing how much fuel enters the cylinder. (which is why hot EGR gases REDUCE exhaust gas temps).
Any richer and the hydrocarbons are incompletely combusted (CO emissions and even unburt HC emmissions climb, while the exhaust temperature drops due to less heat being released by combustion).
In a perfect thermodynamic view you would run at stoich for max hp at all times and limit the air and fuel that enters at each cycle. Unfortunately, the high temps generated from complete combustion climb proportionally with the amount of fuel being combusted in a given cylinder... part throttle leads to very low VE% (say 40% instead of 100 N/A or 130 boosted) and the amount of fuel in the cylinder is fine. At WOT, there is so much heat being generated in the same combustion space that tempertures spike fast as shown by NOx emissions spikes. EGR was used to reduce these temps and hense the effective VE/BSFC. Under boost the intake charge is even hotter and spikes to hotter temps which can melt pistons, tulip valves, and kill NOx emmisions.
As a result, even NA engines do NOT run stoich at WOT, or even 85% throttle... they run rich (~12:1 AFR) to reduce the temps while not sacrificing as much hp as if they ran lean to do the same thing (~17:1 would do it if you wanted to... but excess fuel drops to absorb heat is a safer bet).
Boosted engines? heat is an even bigger concern for safety reasons (and is why intercoolers, water injection, and nitrous can have such beneficial hp gains) and they have to go even RICHER than N/A... which INCREASES their BSFC, and why engine of similar max hp, and similar max rpm, need larger injectors in a boosted application.
This is not a new concept, it's been known for YEARS, and by millions of engineers and engine builders.
How can a "turbo engine" be more fuel efficient than a N/A engine?
1) smaller displacement - the HAS to happen. Even if there is no boost, the turbo/blower engine still has inherant power losses over an identically sized engine due to:
a) the decreased DCR nessesitated by the boost levels and in the case of a blower,
b) the hp losses (however minimal it may be when at or near idle... it's still there)
c) the extra weight of the engine/car due to turbo/blower/intercooler (100-200 pounds)
2) Test only at idle, cruise, and part throttle where stoich levels are maintained. Once you go WOT you will never be able to get the same hp out of a given amount of fuel as a NA engine for the need to be rich and power the power adder.
Boost Power Adders are designed to add power capacity, not increase efficiency. Volumetric efficiency? yes... but the extra heat requires adjustements which in the gasoline world involves going rich.
I dare you to show me even 1 boosted vehicle that runs stoich at WOT. If you do, it's got some serious extra weight in the heads, block, or intercooler. That's just the physics at play.
#51
if you designed a turbocharged engine...then it failed to boost through a large portion of its operating cycle...you will have really screwed things up. It would be like driving a car with a small engine with a compression ratio of 8...it would be a disaster. In fact, you could simulate this if you wanted to. You could take a production turbo engine and put on a turbocharger that's twice as big as it should be. A turbo from a big truck. It would be way, way underpowered...and probably never boost until wot. Fortunately, nobody does that. They do the opposite...and use turbos on the small side.
The first thing that gets axed in a modded turbo car looking for performance is this very concept... mapping for low to mid rpms/throttle and accepting massive charge heating at WOT/high rpms. It's NOT a good way to build a sportscar or in this case, a Camaro. Variable turbo tech can help reduce this somewhat, but it's always there... you pick a compressor for your target airflow rate.
So a small turbo is a perfect replacement for displacement? no. Even at peak heat efficiency, it still heats intake charge, and still needs intercoolers (weight) to survive. A much better option is to go with Cylinder deactivation to artificially reduce the displacement when hp demands are low without the equipment to heat and then cool the intake charge.
Again, as evidence of a boosted engine with greater fuel economy (greater efficiency)...look at the supercharged Millenia. Better fuel economy. And more output, too.
If you want a fuel efficient engine you need smaller displacement and higher DCR without compromising AFR. If you can get a turbo to boost at low air flow you better hope its a diesel engine with a 4k redline... otherwise you're in for some serious problems at WOT.
#52
On the other hand, I have seen it with my own eyes on a dyno. I've seen it in books and papers. And the proof is in the cars I pointed to...where the boosted example is more efficient. How can you just ignore the proof? I mean, address why you think these cars are more efficient?
In fact, it's not really open for debate...it's kind of understood within the engine community...
"BSFC is always lower on a turbocharged engine."
http://www.greencarcongress.com/2007...dds_biopo.html
SAE 2007-01-1560 : BMW High Precision Fuel Injection in Conjunction with Twin-Turbo Technology: A Combination for Maximum Dynamic and High Fuel Efficiency
SAE 2004-01-0988 : Advanced Gasoline Engine Turbocharging Technology for Fuel Economy Improvements
I mean, I'll ask you this...have you taken an oem engine, calibrated it, measured bsfc...then taken the same engine, boosted it, and measured bsfc? Out in Seattle, where the big 3 are, maybe?
The big 3 don't calibrate part-throttle operation for max hp. They don't. They all run closed-loop stoich.
Do you know what closed loop means? It means it's controlled to run at constant 14.7 when not at wot.
And how can you say the boosted engine has "inherant" power losses over the identically size n/a engine... when, in fact, output is higher? You do recognize that on identically sized engine - one boosted and one n/a - that the boosted has higher output, right?
Higher volumetric efficiency means higher thermodynamic efficency means higher fuel economy means lower bsfc. It's mathematical.
"Different magnitudes of fuel economy improvement can be obtained by applying the turbocharger to gasoline and diesel engines depending on the utilization of the increased power."
SAE 810004 An Overview of Some Turbocharged Gasoline and Diesel Engine Automobiles
But I'm not really sure of your point, regardless. You said cars don't run WOT in the epa cycle, right?
So you have two cars running the EPA cycle. One boosted, one n/a. Neither go to wot. Both run at stoichiometric. Which one gets better fuel economy in the epa city and highway cycle? Boosted. Sorry, that's reality.
AGAIN - see Millenia. See Solstice. See gas turbo applications in Europe.
#53
The TURBO is not making it more efficient... the smaller DISPLACEMENT is. A turbo engine at WOT with the same hp as a NA engine WILL consume more fuel and have a higher BSFC. There's no getting around it. There's no magic happening at idle or cruise with a turbo that isn't spooled up... turbo engines are NOT more fuel efficient... smaller engines are. Apples and Oranges.
And you still haven't explained, why there are examples of cars with two engines, same displacement, one n/a and one boosted...and the boosted version gets higher fuel economy. You need to focus on that issue if you want to learn from this exercise.
#54
1) ALL the cars you point out has having better EPA milage have SMALLER displacement. That's your savings...NOTHING to do with the turbo being efficient when it isn't even functional.
2) Turbo's are NOT functional at idle and low cruise speeds... they simply are NOT designed to spool up until the throttle is opened up and air flow has increased.
Well, now you're just out in left field. If you take two engines, identical in design...like a 2.3L 4 and a 4.6L 8...the 4 isn't more efficient, in terms of volumetric efficiency or thermodynamic efficiency.
If you want to save gas, you need to get by with less hp... that's a fact. N/A engines can use deactivation to make 4 cylinders fill more efficiently than 8 cylinders with the same air flow... that leads to higher VE numbers (say 40% and 0% in the banks, vs 20% in all 8 without deactivation). The higher VE allows for a better burn. If it didn't work, car manufactures wouldn't do it or see the gains they do. DISPLACEMENT is the issue here. Manufactureres using turbos use displacement decreases to acknowlege the same issue... smaller displacement means higher VE% at a given part-throttle condition. HP demands determine your airflow demands...
And you still haven't explained, why there are examples of cars with two engines, same displacement, one n/a and one boosted...and the boosted version gets higher fuel economy.
I'm still waiting to see:
a) a turbo engine get better fuel effiency than a NA engine of the same displacement. (EPA idle/cruise numbers would be fine)
b) a turbo engine of the same hp as a larger NA engine use as much or less fuel to do so (This would be the BSFC at WOT you use to select fuel injector sizes).
I'm sure with all the calibrating you've done you could spare me one example of turbos breaking the laws of physics...
The truth is that turbo charging makes an engine less fuel efficient (BSFC) at WOT due to the mixture enrichment (than a NA engine of equal hp), but manufacturers DON'T CARE. max hp sells cars, not max hp/gallon. To drive sales further, they reduce the displacement to try and raise EPA ratings which without the displacement drop would be WORSE than a NA engine of the same size.
Last edited by Steve in Seattle; 10-13-2008 at 11:07 PM.
#55
This is pointless, because I'm citing real evidence: quoting SAE papers, pointing to real world fuel economy in vehicles, and describing my experience on dynos...and you're just saying "sigh - I disagree." That's really effective.
Anyways...
2003 PT was 2.4L n/a 19/26mpg.
2.4L turbo was 21/27.
1996 Millenia was 2.5L n/a 20/27
2.3L super was 20/28
There are a lot more examples in Europe (because they care more about fuel economy.) I know, because I summarized them all in a document...but I don't have it in front of me right now.
Yeah, manufacturers don't care about fuel economy...especially in europe where more cars are boosted...
Of course you're right. You're right, you're right... That's why ORT trucks use turbochargers. Because they don't care about fuel economy. And we know Europe is all about performance and doesn't care about fuel economy. And, of course, the people who write SAE papers and calibrate engines for a living don't know what they're talking about...but you do... whatever...
#56
In point of fact, there is nothing to support your contention that the BSFC is the same of higher. It's just your statement.
On the other hand, I have seen it with my own eyes on a dyno. I've seen it in books and papers. And the proof is in the cars I pointed to...where the boosted example is more efficient. How can you just ignore the proof? I mean, address why you think these cars are more efficient?
In fact, it's not really open for debate...it's kind of understood within the engine community...
"BSFC is always lower on a turbocharged engine."
http://www.greencarcongress.com/2007...dds_biopo.html
SAE 2007-01-1560 : BMW High Precision Fuel Injection in Conjunction with Twin-Turbo Technology: A Combination for Maximum Dynamic and High Fuel Efficiency
SAE 2004-01-0988 : Advanced Gasoline Engine Turbocharging Technology for Fuel Economy Improvements
Higher volumetric efficiency means higher thermodynamic efficency means higher fuel economy means lower bsfc. It's mathematical.
"Different magnitudes of fuel economy improvement can be obtained by applying the turbocharger to gasoline and diesel engines depending on the utilization of the increased power."
SAE 810004 An Overview of Some Turbocharged Gasoline and Diesel Engine Automobiles
I mean, I'll ask you this...have you taken an oem engine, calibrated it, measured bsfc...then taken the same engine, boosted it, and measured bsfc? Out in Seattle, where the big 3 are, maybe?
On the other hand, I have seen it with my own eyes on a dyno. I've seen it in books and papers. And the proof is in the cars I pointed to...where the boosted example is more efficient. How can you just ignore the proof? I mean, address why you think these cars are more efficient?
In fact, it's not really open for debate...it's kind of understood within the engine community...
"BSFC is always lower on a turbocharged engine."
http://www.greencarcongress.com/2007...dds_biopo.html
SAE 2007-01-1560 : BMW High Precision Fuel Injection in Conjunction with Twin-Turbo Technology: A Combination for Maximum Dynamic and High Fuel Efficiency
SAE 2004-01-0988 : Advanced Gasoline Engine Turbocharging Technology for Fuel Economy Improvements
Higher volumetric efficiency means higher thermodynamic efficency means higher fuel economy means lower bsfc. It's mathematical.
"Different magnitudes of fuel economy improvement can be obtained by applying the turbocharger to gasoline and diesel engines depending on the utilization of the increased power."
SAE 810004 An Overview of Some Turbocharged Gasoline and Diesel Engine Automobiles
I mean, I'll ask you this...have you taken an oem engine, calibrated it, measured bsfc...then taken the same engine, boosted it, and measured bsfc? Out in Seattle, where the big 3 are, maybe?
#57
In fact, it's not really open for debate...it's kind of understood within the engine community..."BSFC is always lower on a turbocharged engine."
http://www.greencarcongress.com/2007...dds_biopo.html
http://www.greencarcongress.com/2007...dds_biopo.html
SAE 2007-01-1560 : BMW High Precision Fuel Injection in Conjunction with Twin-Turbo Technology: A Combination for Maximum Dynamic and High Fuel Efficiency
http://www.sae.org/servlets/productD...D=2007-01-1560
"Therefore, the new Twin-Turbo power unit offers the same muscle as a much larger normal-aspiration engine".
So WHERE exactly do you think they get the EPA milage gains? SMALLER DISPLACEMENT. This simply would NOT be a paper about fuel efficiency if they used the same displacement. Turbos do NOT decrease BSFC (regardless of blog posts).
SAE 2004-01-0988 : Advanced Gasoline Engine Turbocharging Technology for Fuel Economy Improvements
http://www.sae.org/servlets/productD...D=2004-01-0988
Again, the 8-10% fuel effiency gains only exist in a comparibel turbo engine with 30% LESS DISPLACEMENT. The issue here isn't that the EPA fuel milage can be less in a smaller engine, it's that the same thing is available for ANY smaller engine. When the turbo is spooled, and compressing air, you will need to enrich the mixture (you know, that fancy PE mode fuel table) and you BSFC drops.
Do you know what closed loop means? It means it's controlled to run at constant 14.7 when not at wot.
You can have two engines, same size, one boosted, one not. See Mazda Millenia.
And how can you say the boosted engine has "inherant" power losses over the identically size n/a engine... when, in fact, output is higher? You do recognize that on identically sized engine - one boosted and one n/a - that the boosted has higher output, right?
Higher volumetric efficiency means higher thermodynamic efficency means higher fuel economy means lower bsfc. It's mathematical.
Higher VE is determined by how much charge (air) can be crammed into an engine of fixed displacement.
Here's your problem: Turbos are thermodynamically more efficient than superchargers... but LESS than an N/A setup which has NO compression losses. This is the very reason you see turbos and blowers talking about adiabatic efficiency of a turbo approaching 94%, while blowers are lower (60% to 85%). What do you think is the 100% standard they're using? Adiabatic is a fancy word that describes how much compression can happen without excess heat being generated and imparted on the intake charge.
Second, "higher thermodynamic efficnecy means higher fuel milage". I'll give you the benefit of the doubt here and assume your not talking about adiabatic losses from compression being 0, but instead the actual thermodynamics of the otto cycle. If that's what you meant, then we have another problem.... you're assuming that the thermodynamics/fuel economy is directly related to cylinder pressure (VE)... and it's not.
As mentioned before, the higher temps from turbos and the need to burn MORE fuel for MORE gas expanion to get the same piston velocity as a NA engine (due to earlier exhasut valve opening needed to evac turbo cylinders since the turbine has a nasty habit of reducing gas evac speed) means you simply HAVE to combust more fuel in a turbo design to get the same output hp as a NA engine would. Again, this is why, again, you need more fuel delivery to power a 500hp blown engine than you do a 500hp NA engine REGARDLESS of displacement.
"Different magnitudes of fuel economy improvement can be obtained by applying the turbocharger to gasoline and diesel engines depending on the utilization of the increased power."
SAE 810004 An Overview of Some Turbocharged Gasoline and Diesel Engine Automobiles
SAE 810004 An Overview of Some Turbocharged Gasoline and Diesel Engine Automobiles
So you have two cars running the EPA cycle. One boosted, one n/a. Neither go to wot. Both run at stoichiometric. Which one gets better fuel economy in the epa city and highway cycle? Boosted. Sorry, that's reality.
AGAIN - see Millenia. See Solstice. See gas turbo applications in Europe.
2.5L 170hp V6
2.3L 210hp V6 (supercharged miller cycle)
"Both models have returned similar gas mileage: 21.8 mpg for the S and 21.4 for the base." -- Consumer Guide Auto.com
Yep... notice the 2.3L blower engine had the higher milage and it had even lower displacement. What's that tell you?
1996 Millenia
"2.5L V6 EPA: 20/27=22"
"2.3L V6 supercharged EPA: 20/28=22"
so yet again, we see the blower engine with the same or a bti worse milage, but with a nearly 10% displacement advantage. What's that tell you about it's BSFC? for the engine, it's nearly the same... yet we're comparing tow differently sized engines. Are you suggesting that decreasing the engine size to 2.3L made it LESS fuel efficient, but thankfully the supercharger was there to improve it to stay comperable?
2009 Pontiac Solstice:
2.0L I4 turbo Auto EPA: 19/27=21
2.0L I4 turbo Manual EPA: 19/24=21
2.4L I4 Auto EPA: 19/25=21
2.4L I4 Manual EPA: 19/28=22
So again, we see the turbo engine has nearly identical fuel milage as the NA version that is 20% larger displacement. If turbo charging makes an engine more fuel efficient, why are they the same milage with the turbo having a 20% displacement advantage? becuase the turbo doesn't improve BSFC...
Any other examples? I guarantee they'll be exactly the same... MPG improvements through decreased displacement, not through turbocharging.
#58
BTW, here's an excellent example of why cylinder deactivation, and more importantly a smaller displacement will give you better BSFC: http://autospeed.com/cms/A_110216/ar...popularArticle
About half way down you'll see this chart showing how the more throttle restriction you have, the worse the VE, and hence the worse BSFC becomes. This is exacly why a 5L engine operating at 10% throttle has worse BSFC than a 2.5L engine at 20% throttle. Adding yet ANOTHER intake restriction beyond the thottle (say an turbo compressor that hasn't spooled up yet) and you get even worse BSFC.
About half way down you'll see this chart showing how the more throttle restriction you have, the worse the VE, and hence the worse BSFC becomes. This is exacly why a 5L engine operating at 10% throttle has worse BSFC than a 2.5L engine at 20% throttle. Adding yet ANOTHER intake restriction beyond the thottle (say an turbo compressor that hasn't spooled up yet) and you get even worse BSFC.
#59
Back to the issue at hand:
GM Fuel Economytalking about SAABs prototype 2.0L turbo converted to E100:
Without the knock ceiling typical with pump gas, the E100 turbo can make some crazy hp numbers on par with any turbo diesel but with the added benefit of nearly elliminating particulate and CO emissions. 300hp from a 2L... you could only imagine what they could do with a 6L.
Boy I wish gasoline didn't have that nasty knock issue to deal with.
GM Fuel Economytalking about SAABs prototype 2.0L turbo converted to E100:
On full throttle openings, the turbocharger packs up to 1.2 bar (17.4 psi) boost, without risk of ‘knocking’ from the high octane fuel. It gives the BioPower 100 Concept driver access to the sort of in-gear performance typical of a modern, naturally-aspirated engine of four liters or more. The smooth power delivery - without fossil fuel emissions - takes Saab’s traditional ‘less is more’ turbo philosophy to a new level.
That impressive 150 hp/liter specific power output also indicates considerable potential for engine ‘rightsizing’, giving the driver the performance characteristics of a ‘large’ engine without incurring its additional weight, greater complexity or higher fuel consumption. In this way, E100 offers significant potential to reduce the displacement of an engine - thereby reducing fuel consumption - while still achieving a desired power level.
That impressive 150 hp/liter specific power output also indicates considerable potential for engine ‘rightsizing’, giving the driver the performance characteristics of a ‘large’ engine without incurring its additional weight, greater complexity or higher fuel consumption. In this way, E100 offers significant potential to reduce the displacement of an engine - thereby reducing fuel consumption - while still achieving a desired power level.
Boy I wish gasoline didn't have that nasty knock issue to deal with.
#60
From GM Powertrain Tech:
Notice the qualifier. If max hp is the same, the turbo can come in under the NA engine's EPA ratings using smaller displacement. The displacement is the key here... turbos simply do NOT spool up at idle or off-idle and hence are detrimental to economy at low air flow. You'll also note they aren't comparing which engine does better at WOT... but we all get that idea by now.
1.4-Liter Turbo
The 1.4-liter Turbo engine is a new addition to an engine family that ranges from 1.0 - 1.4-liter displacement. The engine will produce an estimated output ranging from 88 kW/120 hp to 104 kW/140 hp and torque values of 175 to 200 Nm. It will deliver an approximate 8 percent improvement in fuel consumption (compared to a higher displacement naturally aspirated engine with similar output) and will be EURO 5 compliant. Key features include a turbocharger integrated into the exhaust manifold, full variable valve timing, thermal management, flow-controlled oil pump, and a reinforced crankshaft and connecting rod
The 1.4-liter Turbo engine is a new addition to an engine family that ranges from 1.0 - 1.4-liter displacement. The engine will produce an estimated output ranging from 88 kW/120 hp to 104 kW/140 hp and torque values of 175 to 200 Nm. It will deliver an approximate 8 percent improvement in fuel consumption (compared to a higher displacement naturally aspirated engine with similar output) and will be EURO 5 compliant. Key features include a turbocharger integrated into the exhaust manifold, full variable valve timing, thermal management, flow-controlled oil pump, and a reinforced crankshaft and connecting rod
Last edited by Steve in Seattle; 10-14-2008 at 08:10 AM.