Z284ever

Well, the Challenger, as I'm sure you know, is a much larger car than the Camaro, that seats 5, but weighs in, in the same class.

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.

blackflag

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.

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.


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.

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.

And that's because the s/c is more efficient. The s/c can provide the same amount of work - same output - while using less fuel. That's why you have to look at per unit output (bsfc - or fuel per horsepower), and not fuel consumption per liter of displacement.

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.

Steve in Seattle

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.

actually the reason turbos and centrifugal blowers are used in Europe is that they don't boost at low rpms/throttle. Since a majority of driving is at idle or cruise(2k-3k) most turbos/blowers are simply NOT used.

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.

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.

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.

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.

nope... just compare fuel injector sizes and you'll see how off that is.

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.


Volumetric efficiency is NOT equal to BSFC (fuel efficiency).

Next week's lecture: Why boost is NOT equal to air-flow. Tune in early

blackflag

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.

In fact, if an automaker released any car that was running rich throughout the operating range, it would never, ever pass emissions.


So are they used or not? First, the euro driving cycle for economy and emissions runs at low speed and high speed. Second, modern turbocharged engines are designed with small, low inertia turbochargers to boost right off idle. Definitely at 2000rpm or before. So turbochargers are definitely used in the certification cycles.

Trust me, everything europe does is for better fuel economy. Everything.

That's right...when you add the backpressure of a turbo or the belt load of a s/c, it's a loss in energy. But the increase in power from the boost more than outweighs it. So it's a net gain in output. A net gain in output means greater efficiency. Which is what makes them so interesting...especially as gas prices rise. It's interesting, isn't it?

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.)

But that doesn't tell you how efficient the engine is. That just tells you how much gross fuel is used. It doesn't say anything about output or efficiency. That's why bsfc is required.

It's not that different. One runs in knock, and one doesn't. But knock can be controlled through spark advance, or compression ratio, or cam events, or intercooling, or a number of ways... but ultimately turbochargers are used on OTR trucks. Why? Because they care about fuel economy. And they most certainly do increase bsfc, because I've seen it with my own eyes.

Again, that just tells you how much fuel is used. It doesn't tell you how much fuel per horsepower. It's also misleading because different engines/manufacturers use different duty cycles for their injectors...so there's not a direct correlation between injector size and output/displacement.


First, the epa cycles run at highway speeds. They run at high speeds. They run at high loads. They run 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.

Steve in Seattle

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.

Steve in Seattle

which is how you get anemic factory turbo designs like the 80's MR2 which spec'd the turbo to fall off the efficency map at exhasut flow above 4000 rpms... which makes the need to run even RICHER at WOT a bigger problem.

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.

More MAX output... the smaller displacement in ALL your examples is the EXACT proof of this whole arguement. 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.

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.

blackflag

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

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?

Is it 'scarry?' Read my quote. I never said max hp. And I said NOT at wot. So now you're just mischaracterizing what I said.

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.

Again, what you're saying just doesn't make sense and isn't borne out in reality. Why do you HAVE to have smaller displacement? 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.

"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'm not even sure who you're arguing against here. I never said stoich at WOT.

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.

blackflag

We're not in the 80's anymore. Why don't you address the more modern cars I pointed you to, where the boosted example gets higher fuel economy?

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. That's just silly.

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.

Steve in Seattle

Alright.. I'll type slow so i dont' lose you here.

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.


*sigh* read it again.

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...

sigh... i have yet to see an example. EVERY car you listed used a SMALLER displacement engine on the turbo to get milage gains... and the max hp numbers go up due to turbo boost at high air flow numbers. NO WHERE in ANY of this discussion have you shown how a TURBO can make your BSFC drop to N/A levels... because it can't be done. It can get close, but not equal or BETTER as you claim.

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.

blackflag

"sigh sigh sigh"
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.


Are you going to offer any proof besides your opinon? I've given papers, websites, examples of cars, and my experience. You give...your opinion based on nothing?

Yeah, manufacturers don't care about fuel economy...especially in europe where more cars are boosted...

Let me bottom line it for you: wot is irrelevant. People don't drive constantly at wot. And neither the epa city nor highway cycles are at wot for 95% of vehicles. So back here in the real world... where people care about real world fuel economy and not wot... boosted is higher efficency, lower bsfc.

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...

blackflag

...

Steve in Seattle

I have repeatedly... it has everythign to do with VE% and lower displacement.

Did you seriously just quote a blog posting from an unknown source?

Lol... ok, thank you for proving my point...
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).

"Data on several hundred family sedan production vehicles over a ten-year period are analyzed to compare turbocharged with non-turbocharged engines. It is shown that for the same power turbocharging enables gasoline engine downsizing by about 30%, improves fuel economy by 8-10% while improving torque and acceleration performance."
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.


thanks for the outline.

Again, you're missing the fundamental difference between VOLUMETRIC EFFICIENCY (i.e. max torque you can get out of fixed displacement), and FUEL EFFICIENCY (BSFC... or how much hp you can get out of a fixed amount of fuel). Two VERY different concepts.

faulty logic.

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.

Exactly my point. The entire statement is that if you have an application where a max HP value is needed (cars saels for example ), you can get there with either a large N/A engine, or a smaller turbo engine. The fuel effiency of the turbo engine at WOT (and generating that max hp you need) will be LESS than the N/A engine by its very nature, but the smaller displacement allows for less fuel consumption at idle/cruise speeds when the turbo isn't spooled up (or if it is, is providing very little pressure gains that would nessesitate enrichment). In a diesel engine turbos are total winners becasue there is no need for enrichment... the fuel simply will NOT detonate as in a sparkplug engine using gasoline.

are we comparing engines of the same size? or same max hp? If it's the size, then the NA one wins hands down. If it's max hp, the turbo engine has a LARGE displacement advantage. That however, in NO way proves anything about BSFC... only that smaller displacements are less fuel hungry.

1995-2002 Millenia:
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.

Steve in Seattle

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.

Steve in Seattle

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.

Steve in Seattle

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.