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What compression ratio is too low?

Discussion in 'SVT Shelby GT500' started by DutyCalls, Jan 9, 2019.

  1. DutyCalls

    DutyCalls Member Established Member

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    I have an opportunity to buy some new Manley Platinum series pistons # 594420C for about half price. On Manley's website, its says they are .020" bore and 23CC dish which would give me a 7.79:1 compression ratio.

    I was just wondering if that compression ratio was a bit low for running pump gas on a street car? I have a Gen2R with a 2.4" pulley and i am seeing 18-19PSI with blower cams and long tubes.

    I was also wondering how much power the pistons were able to handle?

    I am not planning on doing the bottom end this year, but if this is a good deal, I don't mind collecting pieces as they come up.
     
  2. Papaw

    Papaw Active Member Established Member

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    That compression ratio is almost a full point below stock. Personally, I think the stock ratio is too low. I'd want to go to 9.5 or so if rebuilding the lower end. You would need more boost just to get to the same hp level if you went lower on the compression ratio, which may require a larger supercharger than the Gen2R to achieve.
    I'd pass.
     
  3. Brutal Metal

    Brutal Metal Well-Known Member Established Member

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    That's too much dish, you want high single digit cc's. I wouldn't want anything lower than 8.5 c/r
     
  4. Catmonkey

    Catmonkey I Void Warranties! Premium Member Established Member

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    Running more cam is a reason to increase compression, not lower it.
     
    VNMOUS1 likes this.
  5. DutyCalls

    DutyCalls Member Established Member

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    Thanks guys....that's probably why they are so cheap
     
  6. boduke0220

    boduke0220 Well-Known Member Established Member

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    way too low. if you have E85 available I would run 10:1 or more. Jon Lund Sr runs 11:1 on his built 5.8
     

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