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compression 9:1-9:5

Discussion in 'Forced Induction' started by integramic, Mar 1, 2004.

  1. integramic

    integramic Member

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    Can anyone tell me why everyone has a 9:5 compression ratio? Wouldn't lower be better? Is it because they don't make many pistons for lower compression?
     
  2. civic15.8

    civic15.8 Senior Member

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    as you change your compression you have to think about how much boost you are running.if you are running 7 lbs of boost ylu dont want to have 7.0:1 compression it would do more bad then good. so that is why people running around 7 to 9 psi run 9.0:1 to10.0:1 compression
     
  3. pissedoffsol

    pissedoffsol RETIRED

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  4. NotUrAverage_Si

    NotUrAverage_Si Senior Member

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    the lower your compression the more pounds per square inch of boost you'll have to run to reach power levels of higher compression motors under boost. for example like the thread from Honda-Tech that B posted:

    the Lancer EVO has an 8.5:1 compression ratio and has to boost 18psi to make 271hp. If it had a 9.5:1 compression ratio it wouldn't have to boost 18 pounds to reach 271hp. Of course you also have to take the size of the turbo into consideration.
     
  5. pissedoffsol

    pissedoffsol RETIRED

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    read that whole thread. page 2 goes into a lot of good details
     
  6. phunky.buddha

    phunky.buddha Admin with a big stick Admin VIP

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    Arrrrrrrrghhhhhhh

    Reading that thread just makes me want to scream... all those people who think they know what the hell they're talking about, and most of them don't have a clue...
     
  7. NotUrAverage_Si

    NotUrAverage_Si Senior Member

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    what can you do though?

    they're the all knowing HONDA-TECH...they're never wrong remember? :ph34r: :ph34r: :ph34r:
     
  8. phunky.buddha

    phunky.buddha Admin with a big stick Admin VIP

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    Nothing. I'm not going to jump in there and reply to anything. I hate arguing with the holier than thou Honda-Tech crowd. I know what's right and wrong- hell, thermodynamics was my best area while I was in school.
     
  9. pissedoffsol

    pissedoffsol RETIRED

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    granted, theres a lot of retarded posts... but there are sevel smart people on there making good statements. if you can't differentiate between the two, you need better analytical skills, like i need typiing skills :)
     
  10. radnulb

    radnulb Senior Member

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    Read the excellent article on dynamic compression and all in the honda-swap.com articles section.

    Massively oversimplified:

    if (Boost * compression) < (octane * magic) motor runs
    if (Boost * compression) > (octane * magic) motor detonates

    More compression almost always means the more power at a given amount of airflow (boost). There is a lot of fine print on this one, however, since higher compression normally requires more ignition retard in order to prevent detonation, which in turn robs power. Most piston/valve/HEAD designs have a point of diminishing returns where increasing compression necessitates ignition retard to the point where power gains are significantly offset. What this means basically is that you want to run as much compression as you can get away with without needing excessive amounts of timing retard, based on the octane and motor design parameters.
     
  11. phunky.buddha

    phunky.buddha Admin with a big stick Admin VIP

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    Oh I agree with you 100%... I'm just infuriated by the people who think they're right and that the engineer is wrong, when they have no real training or even any experience relating to the matter.
     
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