The performance cars like Preludes say on the dash board to use only Premium fuel

Discussion in 'Prelude' started by LovingPerson, Feb 9, 2004.

  1. LovingPerson

    LovingPerson Guest

    Dear all:

    My Prelude says on the dash board to use only premium fuel.
    That is the fuel I have been using. However, the previous owner says
    that she uses regular normal 87 octane without problem.

    Is it okay for me to not use premium fuel? The way I understand
    it is that the higher octane is used so that higher compression
    engines do not experience pre-mature ignition. I also seem to
    remember from another source that the higher octane prevents Knocking.
    I am wondering if Knocking is the same as premature ignition.

    Could someone tell me if it will be okay to use regular in my
    Prelude? Sincerely. Thx in advance.
    LovingPerson, Feb 9, 2004
  2. LovingPerson

    E. Meyer Guest

    Knocking is the gas exploding rather than burning. It is sometimes called
    premature detonation, though that term literally means it goes off too soon,
    while the piston is still compressing, rather than at top-dead-center.

    The higher octane in premium fuel resists knocking. Actually, that is the
    only benefit to premium fuel.

    Modern cars use feedback from a knock detector and adjust the spark
    dynamically to minimize the problem. IF you read your owners manual, it
    probably says something along the lines of "... use premium fuel, but if it
    is not available, you can use fuel rated at least 87 with reduced

    As long as your knock detector is working, you can try it with regular and
    see what happens. If you start hearing knocking (pinging), or if your gas
    mileage drops significantly, that means the engine is making dramatic
    adjustments to accommodate the lower octane fuel (or the knock sensor
    doesn't work) and you should switch back to premium.
    E. Meyer, Feb 9, 2004
  3. I thought you said you didn't drive it, and it just sits in your carport, and
    that you were selling it?
    Scott in Aztlán, Feb 9, 2004
  4. LovingPerson

    John Ings Guest

    If you don't mind loosing performance. Using lower octane fuel than
    recommended used to be disasterous, but modern engines have knock
    sensors that will retard the ignition to compensate for lower octane.
    You won't get all the power you could be getting however.
    John Ings, Feb 9, 2004
  5. LovingPerson

    Paul Bielec Guest

    It will ADVANCE, not delay the ignition. The knock is produced when the
    mixture self ignites.
    In other words, higher the octane, higher the compression the fuel mixture
    can sustain without self igniting.
    Paul Bielec, Feb 9, 2004
  6. LovingPerson

    John Ings Guest

    Will retard the ignition. In other words delay the firing of the spark
    Correct. And the more ignition advance the engine can handle.
    John Ings, Feb 9, 2004
  7. LovingPerson

    Paul Bielec Guest

    No, it will advance the ignition to fire up the mixture before it
    This reduces the performance of the engine because the ignition happens
    before the highest compression ratio is achieved.
    But it forces the mixture explosion to happen correctly i.e. from the top of
    the cylinder pushing down on the piston. While the self-ignition can happen
    anywhere in the combustion chamber and the forces will push excessively
    against the cylinder walls and the valves instead of pushing mostly downward
    on the piston.
    This reminds me the way they used to destroy cannons centuries ago. They
    would place a bag with gun powder at the cannon's opening. The force of the
    explosion pushing down the cannon towards its dead end would brake the
    Paul Bielec, Feb 9, 2004
  8. I see.
    So what is the optimum ignition timing?
    Fixed at TDC?
    Stephen Bigelow, Feb 9, 2004
  9. LovingPerson

    John Ings Guest

    Self ignition will never occur at the low compression ratios found in
    gasoline engines.
    You haven't a clue what you're talking about sonny!
    While the piston is still on it's way up? Baloney.
    Here is a good online course. Go do your homework:

    Drivel. Any combustion or explosion occuring in a cylinder acts
    equally in all directions. It's not a shaped charge,


    You're as confused as a bottle baby in a topless bar kid!
    John Ings, Feb 9, 2004
  10. LovingPerson

    Paul Bielec Guest

    Here is a good online course. Go do your homework.

    First hint for you. Open and type in:
    "what is engine knock?"

    You'll get a definition, as well as plenty of articles to educate yourself
    on the subject.

    You'll learn that, even in a gasoline engine, an auto ignition can happen,
    especially around the edges of the piston.
    The causes are mostly gasoline with too low octane factor or combustion soot
    deposits inside the cylinders.
    This will cause an undesired flame front, which will travel in wrong
    direction. In extreme cases (engines with no knock sensor),
    it may even bend the piston rod if the detonation happens early in the
    stroke, while the piston is still travelling up.
    These undesired detonations will cause vibrations, which will be detected by
    the knock sensor. The ECU will then advance the ignition.

    Of course, the vibration can be a result of badly adjusted ignition timing
    (engine mods, modified program, fine tunning of racing cars etc.), but this
    is a whole different story and has nothing to do with using regular gas
    instead of high octane gas. In this case, it is the spark plus that lights
    up the fuel at a wrong moment (too early, while the piston is still
    travelling up) and the ignition has to be retarded to correct the problem.

    Before calling someone a "kid" or "sonny", you should learn a little about
    what you're talking about.

    Paul Bielec, B. Eng.
    Paul Bielec, Feb 9, 2004
  11. LovingPerson

    Paul Bielec Guest

    The software in the ECU will trigger the ignition based on several
    The software will vary from one car/engine to another.
    Ideally, you'd want the ignition to happen when the piston has travelled all
    the way up and the fuel mixture is at its higher pressure.
    In practice, it will probably happen when the piston just started travelling
    down, just a guess.
    Paul Bielec, Feb 9, 2004
  12. I see.
    I see.
    Have you ever set ignition timing on an engine?
    What is the base timing for *your* car, Paul?
    Stephen Bigelow, Feb 9, 2004
  13. LovingPerson

    Paul Bielec Guest

    Have you ever set ignition timing on an engine?
    Nope, never changed the timing on any of my cars. Never changed the chip. I
    was always happy with the OEM computer.
    On the other hand, back at university, several of my friends were involved
    in the Formula SAE project. They were designing an engine cotroller unit for
    their car.
    The ECU software was written by the students, members of the project.

    Today, I'm involved with engine controller software but it is not for
    internal combustion engines.

    I was involved in coding of the software for the following engines:

    Not quiet the same power output.
    Paul Bielec, Feb 9, 2004
  14. That wasn't the question.
    What is the base timing for your car?
    Stephen Bigelow, Feb 9, 2004
  15. LovingPerson

    JRK Guest

    That's funny! The site you reference describes setting the timing to fire on
    the way up for performance.
    JRK, Feb 9, 2004
  16. mean before top dead centre?

    Stephen Bigelow, Feb 9, 2004
  17. LovingPerson

    Paul Bielec Guest

    I don't know.
    Paul Bielec, Feb 9, 2004
  18. LovingPerson

    Casey Guest

    John Ings said...
    Funny how saying things like this will often come back to haunt
    Did you bother to read it? You might actually learn something.

    I'm guessing you never used a timing light and a dwell meter on a
    older "non-electronic ignition" engine...


    "It is easier to get older than it is to get wiser."
    Casey, Feb 9, 2004
  19. Retard. Knock sensors retard the ignition. Always.
    Matthew Russotto, Feb 9, 2004
  20. LovingPerson

    John Ings Guest

    Indeed. Such as this one:
    Note the first sentence in the second paragraph:
    "Using a single knock sensor, the system detects the onset of
    detonation and RETARDS the timing on a per cylinder basis"

    Or this one:
    on a knock sensor chip from Texas Instruments. Note the line midway
    down the page:

    "The data from the A/D enables the system to analyze the amount of
    RETARD timing for the next spark ignition timing cycle."
    All correct so far.
    No, it will retard the ignition.
    Most cars fire the plug when the piston is on the way up, unless the
    engine is very large and runs at low RPM.
    I've been setting the timing on cars for 48 years SONNY.
    And you're full of shit.
    Generally as soon as a junior engineer shows up on the shop floor, the
    foreman sends a tech to keep an eye on him and make sure he doesn't
    get into trouble.
    John Ings, Feb 9, 2004
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