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  1. #25
    Newcomer Array
    Join Date
    Dec 2007
    Location
    Melbourne
    Car:
    Integra DC2 Type R turbo
    I agree with a lot of what's being said, yet it is worth noting that if it's to be more than a theoretical discussion a desired outcome should be initially decided upon. If a smallish turbo is to be used, with a modest power figure in mind, than retaining a higher comp ratio would certainly be advantageous. Although if a larger turbo was to be used it then would be reasonable to reduce the compression, run higher boost and achieve your power goals. Even with only 9psi through a gt30 on a properly built motor 200+fwkw is available.
    Of course lag is not purely a function of comp ratio; turbo size and design, manifold design, pipe diameter(bigger is not always better), pipe length, engine displacement and tune all play important roles in minimising lag. I also feel that with a high rev limit a big turbo on a built motor will give you a far greater power band, as it will not run out of puff higher in the rev range.
    All of this means nothing without a good tune, if you go for small turbo/ hi-comp set up or large turbo/built motor neither will live a happy or long life without the right tune.
    Yes you can put a large turbo on a hi-comp motor, it's just that it's like gambling. You may win in the short term but chances are you'll lose in the long run.
    So save money and do it properly once.

  2. #26
    Ozhonda Supporter Array
    Join Date
    Jul 2004
    Location
    Brisbane
    Car:
    MV Agusta F4
    If you have a decent setup and a tuner that knows what he is doing you, will have no problems at what so ever, weather your running high compression and/or a large or small turbo.

    Even with stock internals you can acheive over 200kw @ wheels, B and K series and no reliability problems. Lasts for a long time.
    Deano.

  3. #27
    Member Array
    Join Date
    Jul 2006
    Location
    Perth - Ardross
    Car:
    crx gen 1/gen 2
    Quote Originally Posted by FastFwd View Post
    NS dude?

    where u learn that man u sound fairly knowledgeable.
    I belong to a local club were we do technical sessions on various topics. So if you're presenting you do a lot of homework. The information like this is available in various places - its a matter of finding and assimilating it. Plus I have rebuilt engines, assisted with other rebuilds, done engine swaps, and so on.

    To expand on the topic a bit, the maximum cylinder pressure in an NA car varies between 900 and about 1400 psi. Boost it or up the compression ratios and you start looking at 2000 psi. Thats why getting that point correct is important - 2000 psi at tdc means you bust the bearings pretty quickly. Get it too late and you waste the effort. Arranging things to get it correct is the tuner's art.
    Get pre-ignition (knock) and you start seeing 3000 psi plus spikes which busts pistons and rods.

    Re the more general discussion on small or large turbo and starting cr, everything I see agrees with isitqik and DL001- its the total package and how its put together that determines a lot of what you get. Talk to the people who have experience with your motor, know what your goals are and where you will use the motor, and go with 'that' package.
    And then don't go a change it up without getting it retuned!
    anjin

    aka ian

  4. #28
    Member Array
    Join Date
    Mar 2006
    Location
    Perth
    Car:
    JDM EG Built B16a2 Turbo
    Quote Originally Posted by anjin View Post
    I belong to a local club were we do technical sessions on various topics. So if you're presenting you do a lot of homework. The information like this is available in various places - its a matter of finding and assimilating it. Plus I have rebuilt engines, assisted with other rebuilds, done engine swaps, and so on.

    To expand on the topic a bit, the maximum cylinder pressure in an NA car varies between 900 and about 1400 psi. Boost it or up the compression ratios and you start looking at 2000 psi. Thats why getting that point correct is important - 2000 psi at tdc means you bust the bearings pretty quickly. Get it too late and you waste the effort. Arranging things to get it correct is the tuner's art.
    Get pre-ignition (knock) and you start seeing 3000 psi plus spikes which busts pistons and rods.

    Re the more general discussion on small or large turbo and starting cr, everything I see agrees with isitqik and DL001- its the total package and how its put together that determines a lot of what you get. Talk to the people who have experience with your motor, know what your goals are and where you will use the motor, and go with 'that' package.
    And then don't go a change it up without getting it retuned!
    Im nor agreeing or disagreeing im just saying it sounds like you know what your talking about. I'm not close to a mechanic but ive done everything myself over the years ive had my civic/s15 and i've learnt everything i know. I've gone for the engine build myself as the high comp didnt work out so well for me in the past but i think that was cos the tuner made a mess of it.
    Fastfwd Photoshoot cover pic Click here!

  5. #29
    Member Array
    Join Date
    Jul 2006
    Location
    Perth - Ardross
    Car:
    crx gen 1/gen 2
    It does help that a close mate is a mechanical engineer who does similar builds and who corrects me when I get off beam, but yes its about learning and doing yourself. A necessity for me with a 1983 model crx - try fixing that at the Honda dealer workshop. I've had everything in and out of that car and a previous one, so nothing much bothers me anymore.
    anjin

    aka ian

  6. #30
    Member Array
    Join Date
    Sep 2005
    Location
    Perth
    Car:
    DA9, eg, n360,
    they still fix old hondas in the dealer workshops...

    there is a point where to small of a turbo is a waste of time it becomes a bottle neck of the engine...

    its like having 2inch pipes on the exhaust manifold but only run 1inch exhaust

  7. #31
    I agree that its almost all in the tune. Im running 15psi with a greddy T518z in an s2000 on stock compression. Should be looking at a ECR of around 21-22. The car runs great thanks to the boys at Willall racing.

  8. #32
    Member Array
    Join Date
    Mar 2006
    Location
    Perth
    Car:
    JDM EG Built B16a2 Turbo
    wow s2000's can run 15psi on stock compression. I didnt know that, thats awesome.

    What's the stock comp?
    Fastfwd Photoshoot cover pic Click here!

  9. #33
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    Join Date
    Apr 2005
    Location
    Melbourne
    Car:
    dc2r
    shouldnt it start knocking at 14 ecr

  10. #34
    Member Array
    Join Date
    Sep 2005
    Location
    Perth
    Car:
    DA9, eg, n360,
    if u sort out the timing and the fuel... it should b fine

  11. #35
    Stock compression is 11:1.

    Yeah my tuner is really good, plus Im running on E85 fuel allowing me to run slightly more boost as per 98.

  12. #36
    > plus Im running on E85 fuel

    I think this has a LOT to do with it.

    > say i raised the comp to 12:1 instead of 10.2:1 ill get a better response

    I think on a Honda the compression ratio's you'd be considering are in the range of 8 to high 10's : 1.

    The 12:1 ratios and higher are specific to highly tuned pushrod V8's turning really high RPM.

    I think NASCAR V8's topped out at about 16:1 some time ago, but racing rules have been introduced to limit this with a view to moderating costs.

    Higher ratio's are often used when turning really big RPM's and the cylinder VE isn't the best. By squashing a cylinder with an 80% VE with very high CR the cylinder pressure is the same as a 100% VE with less compression.

    Not as application on a street engine with an 7000rpm redline.

    Any form of alcohol changes this a lot.

    Nick.

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