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Scion MPG-Real World Numbers

191012141525

Comments

  • aathertonaatherton Posts: 617
    Alternating tanks of 87 and 91 is going to make a mix varying around 89, if the fill-ups only put 7-8 gallons in a tank that holds almost 12. So the effect of premuium gas on mileage would be hard to discern. You would be running on 88-90 all the time. To get a tank of 91, do two premium fill-ups in succession.

    Another factor makes the effect of premium even more difficult to discern. Premium is only of benefit in preventing the knock sensor from operating, and the knock sensor only operates at heavy throttle and/or high rpms. And for premium to affect the mileage of a whole tank of gas, you need to spend a lot of time at those conditions.

    If you are driving gently for economy, you will not see any improvement in mpg from premium. If you sometimes use full throttle for passing or high speed, you may feel the extra power from premium under those conditions. And when you use those conditions, less premium is required than regular to make the same power. If you use those conditions a lot, the increased mpg from premium becomes discernable.

    However, under the hardest continuous driving, the difference between a tank of regular and a tank of premium is maybe only 2 mpg. For most hard drivers, the difference may only be 1 mpg. For the average driver, the improvement will be so small that it is overcome by other variables and is not discernable.

    Would you like to see Scion info on (a) the knock sensor or (b) the extra power of premium?
  • icanoeicanoe Posts: 5
    I just purchased the Salsa Red xB this past weekend(automatic). I have only driven it 42 miles, but the gas gauge has not moved. I am not used to THAT!

    I was test driving both the Honda FIT and the xB. The xB won, because of the room, the great airconditioner, and my wife thought it was cute. kudos for me.

    I actually traded in my Grey 2000 Silverado Ext Cab 4X4 Z71 5.3 liter V8. I did really like that truck, but driving back and forth to work, 35 miles, it was eating me alive in fuel costs...at about 14 Mpg or less. If you punched it a few times you could actually see the gas gauge move. When I was a landlord and moving stuff all the time, the truck was great. Now that the property is sold...I just didn't need the truck and the gross fuel economy. I am glad I made the switch. Stay tuned for my MPH...I'll update it in a month..not like the truck where I was spending $200 per month on gas. Now the money I save on gas is my car payment!
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,664
    Yes your comments make sense, definitely. I think what surprised me is that using premium gives me markedly LESS mpg.

    There isn't, of course, any more energy in high test gasoline, or any more "power". It just burns more evenly (the "flame front") in the combustion chamber.

    So, as you say, there are times when a steady even flame front is important to the engine, and other times when it doesn't much matter. It rather depends on what you're doing with the engine at the time.

    It's always been my understanding, from the physics of automobile engine anatomy, that using high test would make more sense in stop and go or heavy duty driving than it would on a flat even highway.

    I do think, though, that the xA runs better on high test, regardless of the mpg.

    I don't fill up until about the 350 mile mark, so the tank's pretty empty.
  • aathertonaatherton Posts: 617
    HIgh octane does not burn more evenly or steady. High octane is simply harder to detonate, which means that higher compression can be used. Higher compression makes more HP.

    Conversely, if low octane is used in a high compression engine, it will detonate under load. Detonate means that it will ignite too soon on the pistons upstroke - too many degrees before top dead center. This is knocking which is destructive, can burn a hole in a piston.

    Modern high compression engines like the xB have knock sensors, which retard the ignition at the first few knocks. Retarding the ignition reduces power. Reducing the HP of an engine means more gas is needed to make up the lost power.

    The xB and xA have the same engine and low octane is recommended for both. Both run perfectly on low octane, but will make more power on high octane. In some other post I offered to paste info on the effect of octane on the xB's power, and info on the knock sensor that allows xBs to use low octane gas. But there was no interest.
  • Yeah it does. High octane means a more controlled burn. That's the whole point. You get an even flame front, it's not ragged or spontaneous, and yes, this is due to the fact that it is harder to burn. So we are both saying the same thing differently.

    Personally, I don't think you get any more power out of an xA or xB with high octane. I might try to prove or disprove this on a dyno sometime soon.

    I think what we are sensing is a smoother engine.
  • aathertonaatherton Posts: 617
    "... Personally, I don't think you get any more power out of an xA or xB with high octane. I might try to prove or disprove this on a dyno sometime soon. "

    That has already been done by Scion and reported below.

    2005 xB tested on premium gas
    108 hp @ 6000 rpm
    105 ft-lb @ 4200 rpm
    http://www.automotive.com/2005/12/scion/xb/specifications/index.html

    2006 xB tested on regular gas
    103 hp @ 6000 rpm
    101 ft-lb @ 4200 rpm
    http://www.automotive.com/2006/12/scion/xb/specifications/index.html

    That was the first item I offered to post and it sounds like you asked for it indirectly. But do you understand the reason for the change? The engine did not change.

    The other item was the Scion info on the knock sensor that allows regular gas to be used. Ask and it shall be posted as well.
  • aathertonaatherton Posts: 617
    "... . High octane means a more controlled burn. That's the whole point. You get an even flame front, it's not ragged or spontaneous, and yes, this is due to the fact that it is harder to burn. So we are both saying the same thing differently. "

    We are not saying the same thing at all.

    The "burn" occurs after ignition, and is controlled by the shape of the combustion chamber, piston crown, etc.

    Before the gas burns, it must ignite. And the timing of the that ignition is what octane is about.

    High octane means more resistant to ignition. HIgh octane gas takes more compression and heat to ignite the mixture. So the mixture will not ignite so soon that it tries to drive the piston down backwards before it has crossed top dead center. That would be "knocking".

    The high compression of the xB engine tries to ignite the mixture so soon on the compression stroke that under high engine load or high rpm, either high octane must be used or the ignition timing must be retarded by the knock sensor.
  • From my perspective I think we are indeed saying the same thing. Pre-ignition is basically a ragged burn in other words.

    DYNO TEST--those links only show a 2005 and 2006 both on 87 octane.

    Anyway, I'd like to do the dyno test at my friend's shop. It is so easy to misinterpret dyno data or fudge the results in various ways---this way I'd get a pretty accurate reading and then I could say or not say what's up with high test on the Scion with some degree of assurance.

    I'm inherently skeptical of any claim to BOTH increased fuel mileage AND increased performance at the same time. That's a rather rare occurrence, but we'll see. I'm open-minded on it. Obviously my own anecdotal testing failed to show any improvements with high test, but the dyno is quantitative. I'll keep you all posted.
  • aathertonaatherton Posts: 617
    "... I think we are indeed saying the same thing. Pre-ignition is basically a ragged burn."

    Before there can be a burn, there has to be ignition. Pre-ignition is the mixture igniting too soon. The result is knocking, where the "burn" drives the piston down in the wrong direction, before it has reached top center.

    To stop knocking, either a higher octane must be used, or the engine must have a knock sensor to retard the ignition. The xB has a knock sensor.

    "... those links only show a 2005 and 2006 both on 87 octane."

    http://www.automotive.com/2005/12/scion/xb/specifications/index.html
    http://www.automotive.com/2006/12/scion/xb/specifications/index.html

    Damn, you are right that the 2005 link does not show that the HP was obtained on high octane. It only lists the recomended 87 octane. The moderator of ScionLife.com said Scion had to de-rate the 2006 engine to 103 HP because it had to be tested on 87 as recommended in the Owners Manual. He said 2005 engine was rated at 108 HP but that was on premium gas and to keep that rating Scion would have to recommend premium, which was not becoming for an economy car.

    I have a thick 2005 Scion brochure which lists the xB at 108 HP.
    These links also say 108 HP for 2005:
    http://www.theautochannel.com/news/2004/12/24/310183.html
    http://auto.consumerguide.com/Auto/New/reviews/full/index.cfm/id/38232/Act/Specs- /

    You may have to dyno test on the two octanes to convince yourself that the xB makes 5 more HP on high octane, because the knock sensor does not intervene to retard the igntion under maximum load.
  • aathertonaatherton Posts: 617
    "... don't think you get any more power out of an xA or xB with high octane."

    The ball is in your court on the issue of whether the engine makes 5 more HP on high octaine.

    Let's see if we agree that these are facts:

    1. The 2005 xB was advertised by Scion to make:
    108 hp @ 6000 rpm
    105 ft-lb @ 4200 rpm

    2. The 2006 xB was advertised to make:
    103 hp @ 6000 rpm
    101 ft-lb @ 4200 rpm

    3. The Owners Manual, Section 2, Page 114 says:
    OCTANE RATING
    Select Octane Rating 87... or higher.
    Use of unleaded gasoline with an octane rating or research octane number lower than stated above will cause persistent heavy knocking. If it is severe, this will lead to engine damage.

    Now let's see what you think of these statements:

    1. There was no change to the 2006 engine to cause the reduced power and torque.
    2. 87 octane is the minumum that the engine will run on without knocking.
    3. The engine has a knock sensor that retards the ignition to stop knocking.
    4. Retarding the ignition reduces power.
    5. The knock sensor cannot retard the ignition enough to prevent knocking on octanes below 87.
    6. The octane language in the 2005 and 2006 Owners Manuals is the same.
    7. The words "or higher" after 87 octane are significant.

    And what you think of these unsupported statements from a moderator of ScionLife.com who said he got it from a source:

    8. Scion tested the 2005 engine on premium gas.
    9. For 2006 Scion was told to either (a) retest the engine on the 87 octane gas recommended in the Owners Manual, or (b) explain that the engine would run on a minumum of 87 octane but made more power on premium. Scion chose to stay with the present language in the manual, and so had to de-rate the engine to 103 HP using 87 octane.

    If you agree with statements 1-7 but do not agree that statements 8-9 are valid, then please offer another explanation for the loss of power for 2006.
  • I couldn't say without more information. What you may be seeing is a correlation but not a cause and effect, in what you are reading.

    All I know for sure is that I always get worse fuel mileage when I use premium in my xA. Never fails. Why, I don't pretend to know. Just an observation. Usually drops about 2 mpg---which could in fact, just be a statistical variation.
  • aathertonaatherton Posts: 617
    You originally said: "Personally, I don't think you get any more power out of an xA or xB with high octane." I then presented a case that they do make more power on high octane.

    This is vital information for many people who are seeking an extra 5 HP by adding expensive modifications, such as intakes, exhausts, and pulleys. They may draw their own conclusion on how the 2005 engine made 5 more HP with no modifications, and how this applies to the 2006 engine.
  • I really don't believe their HP ratings have anything to do with the fuel. Must be engine-design related.

    Here's an interesting article that explains why higher octane might even produce less HP, which I think might be happening with my car.

    http://www.motorcycle.com/mo/mcnuts/rt-fuel1.html

    Anyway, it's fun to explore the issue.

    Maybe others have comments?
  • aathertonaatherton Posts: 617
    "... I couldn't say without more information. What you may be seeing is a correlation but not a cause..."

    Here is the information on the knock sensor, which reduces the power when kocking happens on 87 octane. On less than 87, the knock sensor cannot stop the knocking:

    Owners Manual, Page 114:
    OCTANE RATING
    Select Octane Rating 87 or higher.
    Use of unleaded gasoline with an octane rating or research octane number lower than stated above will cause persistent heavy knocking. If it is severe, this will lead to engine damage.

    Tech Literature:
    1NZ-FE ENGINE (ENGINE CONTROL SYSTEM)
    1. General
    The engine control system has following system.
    ESA
    Electronic Spark Advance
    Ignition timing is determined by the ECM based on signals from various sensors. The ECM corrects ignition timing in response to engine knocking.

    Tech Literature:
    DIAGNOSTICS - SFI SYST
    DTC P0325
    KNOCK SENSOR 1 CIRCUIT
    CIRCUIT DESCRIPTION
    Knock sensor is fitted on the cylinder block to detect the engine knocking. This sensor contains a piezoelectric element which generates a voltage when it becomes deformed, which occurs when the cylinder block vibrates due to knocking. If engine knocking occurs, the ignition timing is delayed to suppress it.
  • aathertonaatherton Posts: 617
    "... Here's an interesting article that explains why higher octane might even produce less HP, which I think might be happening with my car. http://www.motorcycle.com/mo/mcnuts/rt-fuel1.html ..."

    The article says:
    "... leaded high-octane race fuels burn slower than most unleaded fuels, and may reduce performance in stock or lightly modified motorcycles...."

    Have you been putting high octane leaded racing fuel in your xA? You can only get that at race tracks and airfields.
  • aathertonaatherton Posts: 617
    "... I really don't believe their HP ratings have anything to do with the fuel. Must be engine-design related."

    After all the information posted above, why don't you believe that HP is reduced whenever the knock sensor operates to retard the ignition on 87 fuel?

    You must not believe that retarding the ignition timing reduces power - that is where you are coming from. But the relation of timing advance to power is basic engine mechanics.

    As for a change in 1NZ-FE engine design from 2005 to 2006, I have not heard of that, and it does not show in the published specs. Do you have any details?
  • That's correct, I don't believe high octane fuel will produce any more HP.

    But I don't wish to dominate the conversation so let's have other comments or anecdotal evidence on Scion fuel mileage.
  • aathertonaatherton Posts: 617
    "... I don't believe high octane fuel will produce any more HP."

    “… Our first acceleration times for the GXP were somewhat slower than Pontiac’s claims, and company officials suspected our car may have been delivered – and then tested – with regular fuel. After we retested with premium, the GXP redeemed itself, blasting to 60 mph in 5.6 seconds and through the quarter- mile in 14.2… big improvements of 1.1 and 1.2 seconds, respectively…”
    --Car & Driver, October 2006, page 119, “Road Test Soltice GXP”
  • that's not producing horsepower...that's just the engine mapping advancing the timing. That engine can utilize the premium fuel, but the fuel itself has no more power in it than regular. In other words, the regular may have robbed the engine of its horsepower rating, not the other way 'round.

    So if your engine can't advance timing *substantially* to accomodate the higher octane, then premium fuel will do nothing whatsoever for performance.

    If the engineers built the engine to run on 87, that's probably where the engine's full HP will reveal itself.
  • "... the (premium) fuel itself has no more power in it than regular... the regular may have robbed the engine of its horsepower rating... if your engine can't advance timing *substantially* to accomodate the higher octane..."

    That's what I was thinking, and assuming that the engine could advance timing as much as higher octane would allow.

    But I asked Scion Customer Experience via the link on Scion.com, and was surprised to hear that gas had nothing to do with the reduction in power. Apparently there is no power advantage to octane higher than 87, so I am going back to 87.

    From: Scion
    Date: Fri, 01 Sep 2006
    To:
    Subject: Scion xB horsepower and torque [Incident: 060901-000071]
    ... The difference in the xB's horsepower rating from 2005 to 2006 is reflective of revised testing standards for horsepower set forth by the SAE. The engine design, engineering, and fuel used remains unchanged. The difference is due to the fact that previous testing for horsepower from engines did not include the parasitic drag associated with the operation of a power steering pump. The SAE revised their testing standards to test with a power steering pump operating with the engine.
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