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Thread: Advancing ignition timing - what it means for your cylinder

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    Advanced Tech? verified Feedback Score 0 i3igpete's Avatar
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    Advancing ignition timing - what it means for your cylinder

    Consider the simulation I ran with a predictive combustion model. Though it's just a simple 4-cylinder model, the same applies for all gas engines. Spark timing has been varied from -18 to -10 degrees. a/f ratio is the same throughout. you may be wondering why the peak power does not go up much. recall from your thermodynamics class that the integral of the PV diagram is the actual work produced by a heat engine. timing increases power by pushing the peak in the corner higher and higher. boost adds power by shifting the entire curve upward.

    of course every engine is different, but the principle of how timing adds power is the same. Every car will continue to add power up to a point, at which point the car will begin to lose power as the burn rate happens too quickly before TDC. Of course, the takeaway message here is that even before this point, you're building power at the expense of cylinder pressure (as seen in the P-V diagram). not a good way to build power when you have concerns about lifting the heads.

    this is why i cringe when people use the stock ECU without an ITC or emanage to pull back timing. the factory timing is just way too advanced for anything other than a overspun turbo or n/a engine. choosing the right injector size doesn't change this fact, since the entire map, even the "meaty" part is way advanced.

    Maddog Performance Engineering

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    LW fears my posts Not Verified Feedback Score 1 (100%)
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    Mmm... how many years has Matt held the fastest 3S record with just a ARC2?

    Obviously, having timing control makes it much easier to achieve peak horsepower, but it's been proven to not be necessary to still run great times.

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    Quote Originally Posted by UTRacerX9 View Post
    Mmm... how many years has Matt held the fastest 3S record with just a ARC2?

    Obviously, having timing control makes it much easier to achieve peak horsepower, but it's been proven to not be necessary to still run great times.
    He uses an ITC, as Pete stated he should.

    Jeff

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    LW fears my posts Not Verified Feedback Score 1 (100%)
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    Really? Since when? I know for years all he had was the ARC2. Hopefully Matt will chime in on this.

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    rawr. verified Feedback Score 4 (100%) Atrosity's Avatar
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    Is matt even on this board yet?

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    Quote Originally Posted by Atrosity View Post
    Haha, shameless plugs.

    So, Pete, these are all simulations, right? If the graph in the top left is accurate, then why do people run advanced timing (say past -18* point on your graph) at all if it doesn't affect power? Just to keep cyl pressures down?

    EDIT: I think I'm getting my negatives mixed up. -18* before TDC is more advanced than -10* before TDC :derr:
    Last edited by B-Man; 09-17-2010 at 03:11 PM.
    '92 Dodge Stealth RT/TT - Aug. 2012 COTM

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    Member verified Feedback Score 1 (100%) B-Man's Avatar
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    Do you really think stock timing is already past MBT?

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    Advanced Tech? verified Feedback Score 0 i3igpete's Avatar
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    it might not be, but here's the rub. sure, you'll build more power advancing it to MBT, but is it worth the cost of higher cylinder pressures? law of diminishing returns comes into play, and i'd rather turn up the boost a small bit.

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    What about the 99/98 people able to flash their ECUs... whats your view point on them? Should they retard their timing with anything other than stock turbos?

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