2009 Subaru Impreza line changes?

[AKLGT]

If they build a Spec B with a DSG box and closer to 300 hp to boot, I can almost guarantee I will have one. Unless the price tag is absolutely ridiculous! I love my 08 STI, but I still love driving my 05 LGT 5EAT around town. It's just so smooth and classy looking imo. The STI is a joy for the track and hurling myself around cones, but for daily driving, I really have to say that I prefer the LGT.

 

However, if they bump the power on the LGT, they'd have to bump the power on the STI as well because that is Subaru's "power" horse. It's going to be very interesting to see what happens with the next gen Subies... all the way down the line.

[mikesae]

I know it's not gonna happen but for the LGT, I'd like to see the current power ratings maintained, but with greater fuel economy.

[IwannaSportSedan]

If they would follow Porsche's lead and DI their boxers, they would have more power AND better fuel economy. Possibly even on low-octane.

[rudy]

If they would follow Porsche's lead and DI their boxers, they would have more power AND better fuel economy. Possibly even on low-octane.

 

Doubtful on the latter point. If they add DI, they'll up the compression, which almost certainly will require premium. I don't see what the big deal is, premium is 20 cents more a gallon than regular, so you're talking less than $3 a tank difference.

[IwannaSportSedan]

that is true, but lower octane gas burns easier, and more completely. more complete burn gets the energy out of the fuel, and leaves less particulate matter behind. more of it gets combusted and broken down into simpler gasses.

 

If you eliminate pre-detonation by directly injecting the fuel, there isn't THAT much requirement for higher octane ratings which make fuel harder to completely and quickly combust.

 

And DI with a turbo can only raise compression so far before parts fail under load. Static compression plus forced induction = a lot of pressure.

[Jon in CT]

that is true, but lower octane gas burns easier, and more completely. more complete burn gets the energy out of the fuel, and leaves less particulate matter behind. more of it gets combusted and broken down into simpler gasses.

 

If you eliminate pre-detonation by directly injecting the fuel, there isn't THAT much requirement for higher octane ratings which make fuel harder to completely and quickly combust.

Total nonsense.

[IwannaSportSedan]

Exactly HOW is that nonsense?

 

It is completely rude to refute someone without actually making your point.

 

Do you know what octane ratings are a measure of, and what they pertain to?

[krzyss]

They (octanes) are definately not to measure completness of burning process.

 

Isn't it rude it propagate nonsense?

 

http://en.wikipedia.org/wiki/Octane_rating

 

enjoy reading

 

Krzys

[IwannaSportSedan]

BTW, Wikipedia is not the most reliable source to reference, but for these purposes we'll assume that it isn't inaccurate.

 

It should be noted that octane rating does not relate to the energy content of the fuel (see heating value), nor the speed at which the flame initiated by the spark plug propagates across the cylinder. It is only a measure of the fuel's resistance to autoignition.

 

Fuel that is resistant to autoignite is by definition, harder to burn completely. Fuel that resists autoignition, resists ALL FORMS of ignition. If it is harder to oxidize, it is always harder to oxidize, but of course, not impossible, it just takes more energy. Hotter spark, higher engine temps, and either higher static or dynamic compression, and/or more timing advance.

That resistance has to be overcome at the proper time, to offset resistance to ignite at the WRONG time. That is GOOD for preventing knock, but not the most efficient and complete way to burn fuel.

 

KNOCK is pre-ignition, fuel igniting before TDC, usually in the intake port when the fuel mix hits the hot walls of the cylinder head passages. because fuel is injected before the cylinder head, or carbureted before that point.

 

Increased air pressure from a forced induction device, requiring commensurately more fuel, creates more power, and more heat. More Air/Fuel mix hitting HOTTER cylinder head ports pre-ignites easier.

 

What else can cause more heat? higher static compression ratios and more aggressive advance curve. All serve to make the engine run stronger, but also hotter. Hotter means more potential for pre-ignition.

 

Higher octane, being harder to ignite and burn, resists that.

 

OK. Remedial chemistry lesson taking effect so far???

 

Part 2. Direct Injection. Injecting fuel DIRECTLY into the cylinder through the combustion chamber. Also, by definition, much closer to the time of ignition by the spark plug.

 

So. Fuel is injected just before combustion, and doesn't interact with the intake ports at all. Only AIR in the intake.

 

So... pre-detonation is all but ruled completely out.

 

So why would an engine need higher octane fuel at that point? lower octane fuel does not necessitate lower energy content, or difference in flame front propagation.

 

But, by definition, lower octane fuel is easier to ignite, and thus easier to completely combust ALL of that fuel, instead of pushing unburned hydrocarbons out through the exhaust, to backfire, or burn out catalysts. (post-detonation.)

 

So, if you can directly inject lower octane fuel, and burn it completely, you can actually convert ALL of those chemical bonds to heat, pressure, and thus more kinetic energy into the piston, and through the crankshaft. MORE POWER.

 

ALSO, fuel easier to burn requires slightly less fuel volume per cycle than higher octane fuel to get the same power, and needs to run less rich. Again, less hydrocarbons into the exhaust. More completely burning fuel requires less allowance for a rich mixture for optimum power.

 

There is a reason that burning high octane gas in a car that doesn't require it, gets you WORSE gas mileage, and LESS power than lower octane fuel. An engine has to be tuned to burn higher octane gas more aggressively than lower octane fuel, in order to compensate for needing higher octane fuel to prevent pre-detonation. DI takes Pre-detonation out of the equation.

 

DI is also the first step toward HCCI compression-ignition gasoline engines, that mix the benefits of gasoline and diesel engines by compression igniting gasoline under higher pressure for more output, like a Diesel engine does. But burning thinner fuel gives it some of the RPM and flexibility that gasoline engines have.

 

AGAIN, WHERE IS THIS NONSENSE???????????

[Jon in CT]

AGAIN, WHERE IS THIS NONSENSE???????????

Everything you just wrote, except the Wikipedia quote, is more nonsense.

 

Pre-ignition and knock are two completely different types of abnormal combustion.

 

Pre-ignition occurs when the mixture is ignited by a hot spot on a combustion chamber surface before the spark plug fires. It may or may not provoke knock. Old cars with carburetors and a lot of carbon buildup will sometimes continue running for a short while after the ignition is turned off. This is called dieseling and is the result of pre-ignition. Retarding spark advance obviously has no affect on curbing pre-ignition. Knowing a fuel's octane number tells you nothing about its propensity for pre-ignition.

 

Knock occurs during the power stroke when one or more areas of the end gas autoignite prior to the arrival of the flame front. Octane numbers indicate the fuel's resistance to this type of abnormal combustion.

 

Ethanol has a much higher octane number than gasoline and yet it produces fewer unburned hydrocarbons in the exhaust. Octane number has no relationship to how efficient combustion is nor to how clean/complete the combustion is.

 

Read part 3 of the Gasoline FAQ, unless you wish to remain clueless.

[IwannaSportSedan]

Ok. so I am learning something, but I don't see why what I wrote is completely inconsistent. Perhaps not as specific in the details, or my understanding of the term "knock", but not necessarily inconsistent in the effects.

 

A fuel that is more resistant to knock and power stroke pressure spikes is more resistant to combustion, if pressure and heat have less effect to cause auto-ignition. Pressure and heat are the only things that can really cause auto-ignition. Add spark energy as an input for actual intentional combustion. but still mostly heat and pressure.

 

It still strikes me that a fuel or additive, being less susceptible to auto-ignition, is correspondingly more resistant of any type of ignition, and the actual ignition impulse, started by the spark plug(s) has to be more aggressive with more energy, heat, or pressure, to burn that more resistant fuel over that resistance.

 

So while my explanation might be "glossing over", or slightly inaccurate, the details in that FAQ, the real world effects are not disparate from what I describe. More stable fuel variant that is a bit harder to burn, takes more energy to burn intentionally, but resists unwanted ignition effects.

 

Ethanol is a separate issue, being a different fuel, and a different chemical. Less energy dense, less complex a molecule (fewer chemical bonds to break for simple alcohols like ethanol or methanol), but a higher octane comparison index (stronger, more stable bonds). Alcohol burns very completely because it is alcohol, of course, not because it is higher octane. The same net energy can break fewer, stronger chemical bonds, or more quantity of weaker chemical bonds, as a general principle. I was comparing gasoline to gasoline regarding octane rating, not gasoline to alcohol.

 

Perhaps Direct injection does NOT automatically use lower octane fuel, and knock might still exist. I will concede that point, and welcome the new information.

 

However, other effects of tuning a DI engine, or even other technologies, like ceramic coatings, might negate some of the effects of the engine design that increases the propensity for unpredictable pressure spikes during combustion (knock), also negating the need for premium fuel, even with forced induction and it's associated higher mixture quantities and pressure.

 

Perhaps engineers can develop engines that run at a more consistent, but lower peak temperature, and less aggressively in the combustion chamber, and run lower octane gas more efficiently, even with a turbocharger. The premise is still possible, even if not as simple as I originally thought.

 

 

 

And one more thing.

 

Wouldn't it have been easier on ALL of us, if you had just brought forth this information the FIRST time you responded to me? instead of merely being a heckler, and causing conflict?

 

I have NO problem being corrected, and I welcome the data you have finally put forward. But nobody likes being put down unceremoniously. I am sure you don't either. It makes any of us defensive.

 

Next time, might I suggest, that you offer information in response first, rather than chiding...

[SubieDriver]

But it's the Nasioc way to chide first and don't bother to offer any valuable info at all.

 

Oh, wait, we're not on Nasioc. My bad.

[TrueWhiteBoy]

I kinda prefer to be able to refresh the page and not have 20 new posts

 

Sounds like it'll be a fun car, I actually proposed the same question on NASIOC that AKLGT did in here earlier about wondering what's going to happen to the STI

 

But I don't think I'm entirely up to date and might have skipped a page if someone did mention it

[iowasuby]

I wonder if the changes will really be released on Thursday though. I have a nice deal on an '08 Legacy 3.0R but I like 5 doors better. I wish they'd hurry up, I think Subaru incentives end on Aug. 4

[Jon in CT]

I wonder if the changes will really be released on Thursday though. I have a nice deal on an '08 Legacy 3.0R but I like 5 doors better. I wish they'd hurry up, I think Subaru incentives end on Aug. 4

The 09 Imprezas won't arrive at dealers until around Sept 1 and Subaru's incentives require that you take delivery before they expire.

[Jon in CT]

It still strikes me that a fuel or additive, being less susceptible to auto-ignition, is correspondingly more resistant of any type of ignition, and the actual ignition impulse, started by the spark plug(s) has to be more aggressive with more energy, heat, or pressure, to burn that more resistant fuel over that resistance.

You still don't get it. It's really annoying when someone without even a rudimentary understanding of a subject starts 'explaining' it to others.

 

Here's the situation, at an elementary school level. There's an expanding ball of flame emanating from the spark plug. The portion of the mixture which this ball of flame hasn't reached yet is called the endgas. The temperature of the gases inside the ball of flame is orders of magnitude hotter than that of the endgas. During normal combustion, the hydrocarbon and oxygen molecules in the endgas wait patiently for the flame front to arrive so they can combust in an orderly, controlled, gradual fashion when the very high temperature flame front engulfs them. If the octane level is too low, some of the hydrocarbon and oxygen molecules in the endgas can't tolerate the pressure/heat buildup prior to the arrival of the flame front and autoignite as a group. This produces pressure waves which resonate in the combustion chamber. The main frequency of the sound produced depends primarily on bore size and the speed of sound in the combustion chamber. The sound is called knock or ping.

 

Bottom line: a fuel's octane number has no relationship with how easily it burns.

[IwannaSportSedan]

YOU JUST SAID:

If the octane level is too low, some of the hydrocarbon and oxygen molecules in the endgas can't tolerate the pressure/heat buildup prior to the arrival of the flame front and autoignite as a group

 

HOW, in any realm of chemistry, does being resistant to autoignition due to heat and pressure, NOT MAKE IT RESISTANT TO IGNITION????????????????????????

 

If it resists ignition under heat and pressure, it resists IGNITION PERIOD!!!!!!!!!!!!!! The spark impulse has to be hotter, and the pressure is usually higher due to high static compression or forced induction. Being resistant to ignition does not mean that it can't be ignited, it is a matter of degree.

 

You can NOT say that it resists ignition, but it doesn't. It is either harder to ignite, or it isn't. Perhaps you have a different definition for fuel ignition than fuel burning? Are you going to tell us that those are two different things, now?

 

Maybe basic logic is failing you. I have taken SEVERAL chemistry college level chemistry classes, and did pretty well. I may not have a degree IN chemistry, but I have NEVER heard of a chemical that is hard to ignite, but simultaneously isn't hard to ignite.

 

It isn't that esoteric. It is quite plain.

 

How else do you explain cars that are TUNED to run regular 87 octane gas, that produce slightly *less* power, and get slightly *less* fuel economy when fed higher octane fuel, especially 93 octane.

HOW ELSE CAN THAT HAPPEN, if higher octane fuel is NOT harder to ignite?

 

If higher octane fuel is not harder to burn, the power and efficiency losses should not happen. If higher octane fuel is not harder to ignite, it would not resist autoignition under heat and pressure conditions, and would "knock" just as easily as lower octane fuel. It either is or isn't.

 

 

I am sorry, but what you say defies logic, and chemistry. Maybe *you* should revisit it before you condescend to lecture us mere mortals.

[Jon in CT]

Yet more nonsense. The arrival of the flame front introduces much much higher temperatures to the mixture. Nothing resists combustion unless there are insufficient oxygen or hydrocarbon molecules available.

 

You're an idiot, which I hope most readers have already gleaned that for themselves.

[IwannaSportSedan]

C'mon.

 

Prove me WRONG.

 

Demonstrate how higher octane fuel can be less likely to ignite, as you explain "If the octane level is too low, some of the hydrocarbon and oxygen molecules in the endgas can't tolerate the pressure/heat buildup prior to the arrival of the flame front and autoignite as a group."

 

but yet "Bottom line: a fuel's octane number has no relationship with how easily it burns."

 

Those two statements are at odds with each other. Either the octane rating signifies how much it resists ignition, auto- or otherwise, or it has no relationship. WHICH IS IT?

 

Otherwise, I think you are flat out wrong. You haven't DISPROVEN what I have said, *specifically about ignition resistance* since you chimed in with your rude chiding the first time.

 

I have amended my understanding of "knock", and I am now using the explanation you offered documentation of, and it still doesn't make sense that "a fuel's octane number has no relationship with how easily it burns."

[SubieDriver]

The difference is whether the air/fuel mixture ignites due to the spark plug-initiated flame front or auto-ignites. If the octane is high enough to prevent auto-ignition, then you have a consistent flame front spreading through the cylinder, and you have a smooth-running engine.

 

Too low octane causes auto-ignition, like a diesel, where the ignition is caused by the heat and pressure in the cylinder, rather than the spark plug.

 

Auto-ignition is fine for diesels, but gas engines are not really designed for that.

 

When you have pockets auto-igniting, you have flame-front collisions, which cause shock waves which you hear as pinging or knocking. Also, if too much of the air/fuel gets burned before the piston is at or near top dead center, the explosion will be trying to push the piston down when it's still supposed to be coming up, reducing the power produced.

[IwannaSportSedan]

Ok... Thank you for a reasonable response. Most of what you say makes sense, and there is a definite difference in temperature and pressure between end gasses, and the flame front. And you do seem to be describing knock consistent with Jon's source, the Gasoline FAQ he mentioned.

 

However, that isn't my point. My point is that the energy required to ignite gasoline is higher corresponding the octane rating.

 

a more stable gasoline hydrocarbon molecule (higher octane comparison measurement), that resists a combustion reaction before the flame front reaches it, under increasing pressure and heat, means that the chemical bond arrangement in that molecule requires more energy input to start that reaction to break those bonds.

 

Breaking those bonds releases the atomic bond energy contained there, and allow the hydrocarbons to progressively break down into mostly carbon and hydrogen, and re-combine with the oxygen and other gas elements in the air mixture (like nitrogen) instead, in an oxidation reaction. It results in mostly CO2, and H20, and some other nitrogen based simple compounds. It is air, not pure oxygen, after all. But for every mole of fuel and air that get combusted, it takes some energy in, and releases a lot more energy out. The energy input is what I am discussing.

 

Am I OK, so far?

 

Ok, so if those chemical bonds in higher octane gasoline require more energy (heat energy or pressure-kinetic energy from molecular collisions) to start oxidizing by combustion, that means that those molecules exhibit those characteristics ALL THE TIME. They ALWAYS take more energy to start combusting. It takes more energy than there is available in the end gasses, and it uses more energy present in the flame front. The basis for the octane measurement doesn't change in the fuel molecule between the end gas stage and the flame front. Energy input is static, it is just a matter of it being above a certain threshold in the end gas stage.

 

In a high compression situation (additional pressure), or a high dynamic compression (forced induction) situation, increased pressure usually adds the energy needed to overcome the ignition resistance for those fuel molecules to combust.

 

However, in a lower compression, or lower heat-level engine, (or any situation with less input energy to contribute), there is less total energy in the flame front, some of which gets used to ignite more of the fuel molecules, some of which creates pressure, and results in kinetic energy into the piston face, driving it "down" and creating crankshaft rotation. That is the whole point, is it not?

 

With higher octane fuel in that lower energy engine, less of the fuel gets combusted before the cycle ends, and the ambient residual energy level falls low enough to stop the flame front, which happens earlier with fuel more resistant to ignition.

 

A less stable (lower octane) molecule requires less input energy to break the bonds, which are still mostly Carbon-hydrogen bonds with the same potential energy, but in a less stable arrangement, and more readily releases the stored energy in the molecule. It is less resistant to ignition. ALL the time, in every circumstance. It conserves more of the flame front energy to burn the rest of the molecules, which also have lower ignition energy thresholds.

 

Chemically speaking, either the fuel requires more input energy to start combusting (the definition of the word "ignition") or it requires less energy.

 

The variance between more and less is the difference between autoignition, pre-detonation, and "knock", or ignition on the flame front, as it is supposed to.

 

But the difference between more and less is ALWAYS fixed, as measured compared to heptane and iso-octane, and figured into the "Octane rating" measurement. 93 octane being MORE, and 87 octane being less, as examples. 87 is 87, and is always 6 points less than 93. It is the definition of the measurement. It may not mean joules or calories per mole, or anything, but the measurement is a measurement.

 

The Octane measurement accounts for a mix of molecules in a ratio, not a homogenous volume of molecules of ALL the same arrangement or even the same chemical. Gasoline isn't a single element or compound molecule, but a mixture of fairly light hydrocarbons compared to thicker petrochemicals like diesel/fuel oil, and lubricant oils. If Gasoline were homogenous, we would call it by whatever chemical it was. Pentane, Hexane, Butane, Octane, etc.. Those are homogenous groups of all of the same molecule in volume.

 

The Octane rating gauges the behavior of the mixture as an aggregate, gauging the behavior on a larger level than molecule by molecule, a little bit like measuring the even consistency of concrete, concrete is still a mix of things making up the whole substance of concrete. It is an average measurement of the whole mixture. Octane rating is a little bit like measuring the consistency of ease of combustibility of the fuel. The analogy is a bit clumsy, but not entirely wrong, as far as I understand organic chemistry.

 

That means that the octane rating correlates directly to the fuel requiring more or less energy to ignite, and what I referred to as harder or easier to burn, respectively.

[SubieDriver]

I'm not a chemist, but followed what you said. I agree with most of what you say.

 

Regarding the temp difference between end gasses and flame front - if you're getting auto-ignition, the temps will be similar, because you have the air/fuel mixture burning in both end gasses and flame front. For any given octane, the fuel should burn at a fairly consistent temp, no matter how it was ignited.

 

You want the flash point to be high enough so that you don't get auto-ignition from the latent heat and compression, but low enough to be ignited by the spark plug. The higher the octane, the higher the flash point, which requires higher temp/pressure to ignite it. Conversely, lower octane = lower flash-point = higher risk of auto-ignition, for a given compression ratio.

 

If you're getting auto-ignition, you need to either raise the flash point above the latent heat level (higher octane fuel), lower the latent heat level to below the flash-point (lower temp thermostat, or better cooling system), or reduce the compression ratio to reduce the compression-induced heat added in. Do any one of those, and your problem's solved. Of course the easiest one is to get higher octane fuel.

 

Raise the compression ratio, and you're adding in more heat (from the additional compression), and pushing the fuel past its flash point again, requiring a higher octane fuel.

[SBT]

Okay - energetic and enlightening off-topic side-bar discussion. Let's agree that there's more to combustion chamber dynamics than just air, fuel (and its associated octane level) and spark and call it a day. DI may be in Subaru's future, but it's certainly been bench tested here already.

 

Let's get back on topic.

[IwannaSportSedan]

By all means, and thank you, Subietonic.

 

Do we know if any of the special UK impreza models will be coming to the US, along with the split of the WRX auto and manual version into low and higher power ratings, respectively?

[SBT]

By all means, and thank you, Subietonic.

 

Do we know if any of the special UK impreza models will be coming to the US, along with the split of the WRX auto and manual version into low and higher power ratings, respectively?

 

I hadn't heard the potential for a WRX power "split" mentioned previously IIRC.