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Thread: High Comp small port pistons with ae111 head on 7a block?

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    Default High Comp small port pistons with ae111 head on 7a block?

    Hey guys,

    It's time for me to build a 7age as my blacktop has finally started losing compression. It's been my daily driver for the last 3 years and I rarely bothered to put filters on it b/c of the awesome sound.

    I pulled a 7afe from the junk yard and I believe it needs an over-bore. Oversized ae111 pistons are $350 USD plus rings. Overbore 16V pistons are about 90 bucks including rings. so, can I use ae92 high comp pistons with the ae111 head? Any idea what the CR might be? I have a variety of gasket to choose from including 7afe, TRD 20V, and OEM 20V (.4,.8, and 1mm respectively).

    Thanks,
    Grant

    PS, the engine is already interference so no harm there.

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    Veteran timbo's Avatar
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    That wouldn't be safe, as the smallport piston is fly cut for 4 valves as opposed to being cut for 5 valves. Even more so if the final build created an interference motor.

    I guess you could do it as long as there was plenty of valve to piston clearance.

    edit: missed the post script. Go ahead, but I think you have a higher chance of serious failure.

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    Sam-Q came up with a table or document with various theoretical static compression ratios with different combos of heads and pistons for the 7af block I beleive. If someone has a link to it it would be great. I am trying to find it with no luck.

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    It's here.


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    its not THAT much of an issue in regards to the flycut, as the blacktop pistons have a barely noticable if any flycut for the 5th valve. And got beaten to the link by old mate above lol
    RIP Carly - a smile to light the world.
    06/07/2011

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    So it is reasonably safe to say the 7a bottom end will add 1 : ratio of compression over the 4a.

  7. #7
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    Have you/ will you proceed with this idea? curious to see how this turns out

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