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Thread: rasing compression

  1. #1
    Registered User dat240z71's Avatar
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    Default rasing compression

    After some research I have decided to go with a higher compression turbo motor. What I would like to know is what would be the best way to rase the compression on a turbo motor. When I use the LENGINE program there are two options I can go with. First being if I were to put a N42 head on the turbo block it would yield 8:5:1 or if I went with flat top pistons and p90 head it will yield 8:8:1compression. Which will be the better way to rase the compression and why?
    Thanks
    dat240z
    my cars

  2. #2
    Registered User Tommo560's Avatar
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    i dont know a whole lot but i thought that turbo motors had lower compression so that they wouldnt detonate with the extra pressure being pumped in from the turbo.

    therefore i would say that you should leave the compression as it is, maybe up the boost from the turbo. my dad has a supra tt and when the turbo piping came off once it had about as much power as a 1.5 ton astra, indicating it has low compression but the turbo's supply pressure that provides the extra pressure that creates the extra power.

    his car has about an 8:1 compression and runs about 16-19 puonds boost so i suppose the compression ratio you make the motor would depend on the amount of boost you are running.

    therefore in answer to your question i would suggest that maybe you increase the boost supllied by the turbo's and fiddle with the bolt on stuff instead of major engine work.

    dont take only my advice as i said i'm not an ultimate turbo guru but this is just my 2 cents.

    Tom.
    Last edited by Tommo560; 12-22-2004 at 05:02 PM.

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    Charou
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    First things first. To lower compression you need to put in a thicker metal head gasket. Most turbo manufacturers will carry a selection of different head gaskets of various engines

    Hope this has been helpful.

    Alex

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    Garage Queen chickenwafer's Avatar
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    8.8:1 isn't that high of a compression ratio in all fairness. In fact, I think 8.8:1 wouild be good considering the L-series engines had a bombproof bottom end. 9:1 would push it, but 8.5:1 or 8.8:1 and you should be fine.

    Dave
    1974 Datsun 260z manual: garage queen

  5. #5
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    8.8:1 is higher than many TURBO motors. remember he's talkingabout a turbo motor.

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    Registered User zorro's Avatar
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    The P90 head shaved is the much better option. It is a high flow head with larger ports so the air/flow mixture is not restricted like it is in the N42. The N42 doesn't have to be shaved because of the smaller ports it raises the compression. Its a 6 of one half a dozen of the other option, shave head means clearances become critical other wise a valve may say hello to your piston but less air restriction or quick fix high compression but not the efficent burn and with high horsepower cant get the excess air/fuel out......

  7. #7
    beandip beandip's Avatar
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    If you start raising the compression where are you going to find the fuel with a high enough octain to keep from detonation? You can use booster but that will be a real pain in the butt for a driver. Sure you can up the compression and all of that how ever as bambikiller said this is a turbo your dealing with and even '' bullet proof'' Z engines can look like a gernade on a bad day. As what was offered before , look to the boost and maby a inter cooler and hot ignition and cam and 2 1/2 exhoust. 2 cts.
    I'd rather die while I am living than live while I am dieing. CZC 1887 IZCC 12602 Member of NorthWest Z Car Club

  8. #8
    Registered User brianglawson's Avatar
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    if properly tuned a high compression turbo motor is ultra responsive and makes good power....its all in the ignition/fuel tuning...im an sr person in the sx wrld and there are a bunch of people runing 9.5:1 compression on turbo sr's
    Quote Originally Posted by brianglawson
    "Bottles are for babies, real men get Hairdryers"

  9. #9
    Garage Queen chickenwafer's Avatar
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    that's what I was saying- I know this is a turbo motor, I work on turbo motors a lot and have seen many turbo cars running 9:1 compression and being fine. With a good ignition coil, well tunned fuel injection, a big FMIC and a compressor bypass valve, and you'll be fine at 8.8:1 if you run lower than 20psi of boost. Don't forget a hotter cam!

    Dave
    1974 Datsun 260z manual: garage queen

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