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2G 6 Bolt or 7 Bolt Block Question

Posted by Mham2k, Sep 10, 2019

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  1. Mham2k

    Mham2k Proven Member

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    Dallas, Texas
    How much pressure can a 6 or 7 bolt block hold before cracking? 40psi? 50psi? 70psi?

    I'm not referring to internals I'm referring to the actual block itself.

    Trying to understand what they can handle before they have to be filled.
     

    Street Build 410  1

    1996 Eagle Talon TSi AWD
    awd · manual · 2G DSM
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  2. motomattx

    motomattx Proven Member

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    wampum, Pennsylvania
    They don't usually crack, they distort and there is no set number where it will happen, it has alot to do with fuel type and detonation control, people have made over 1000hp with an unfilled block, how much do you plan to make?
     

    Drag Race Build 3K  24

    1995 Mitsubishi Eclipse GST
    fwd · manual · 2G DSM
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  3. bastarddsm

    bastarddsm Proven Member

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    Mendota, Illinois
    From the data I've collected over the years, I'd say anything over 40psi on a 0.020" motor and you are subject to cracking a cylinder wall.

    Certain piston designs can help and hurt. Ratchet ass tunes obviously hurt things, if you need 1/2" head studs and a mls to keep it sealed at 40psi, you are going to be more prone to trouble.

    Higher compression motors hurt it too.
     

    Showcar Build 5K  1

    1991 Eagle Talon N/T
    9.805 @ 144.00 · 1G DSM
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  4. Mham2k

    Mham2k Proven Member

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    Right now just wondering for the future. Couldn't find a clear answer on it.

    Some fill some don't, haven't seen anyone say they cracked one.
     

    Street Build 410  1

    1996 Eagle Talon TSi AWD
    awd · manual · 2G DSM
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  5. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    Independence, Kansas
    My son cracked a 7 bolt cylinder wall in the exact fashion that @bastarddsm describes. He said 36psi, but I know my son, was probably at 40 on a .020 7 bolt block. #4 cylinder cracked. Was tuned professionally, just didn't like the boost pressure, is my thought. He wanted to throw his internals into another block but his are .020 pistons so he said he would rather buy new pistons for a standard block. Food for thought.
     

    Street Build 4K  28

    1992 Eagle Talon TSi AWD
    awd · automatic · 1G DSM

    755  14

    1990 Mitsubishi Eclipse GSX
    awd · manual · 1G DSM

    548  18

    1967 Chevrolet Camaro RS
    rwd · automatic · Misc Vehicles

    Street Build 775  7

    1998 Eagle Talon TSi
    fwd · manual · 2G DSM

    Street Build 6K  11  25

    1990 Eagle Talon TSi AWD
    13.620 @ 108.460 · 1G DSM
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  6. Mham2k

    Mham2k Proven Member

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    Dallas, Texas
    Gotcha, how do you get away with new pistons for a non new Standard block. Find one with decent cylinder walls, hone, and drop in?

    Sounds like it more safety than really allowing much more boost.
     

    Street Build 410  1

    1996 Eagle Talon TSi AWD
    awd · manual · 2G DSM
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  7. Mham2k

    Mham2k Proven Member

    194
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    Joined Feb 8, 2008
    Dallas, Texas
    This is exactly what I was looking for, thanks
     

    Street Build 410  1

    1996 Eagle Talon TSi AWD
    awd · manual · 2G DSM
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  8. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    Independence, Kansas
    Yep, I had an old 7 bolt block that I tore down for him. It was standard bore but had been left outside for a number of years and it had some rust pitting in one cylinder that would never hone out so he needs a standard bore 7 bolt block and needs to buy a standard set of replacement pistons.
     

    Street Build 4K  28

    1992 Eagle Talon TSi AWD
    awd · automatic · 1G DSM

    755  14

    1990 Mitsubishi Eclipse GSX
    awd · manual · 1G DSM

    548  18

    1967 Chevrolet Camaro RS
    rwd · automatic · Misc Vehicles

    Street Build 775  7

    1998 Eagle Talon TSi
    fwd · manual · 2G DSM

    Street Build 6K  11  25

    1990 Eagle Talon TSi AWD
    13.620 @ 108.460 · 1G DSM
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    Mham2k likes this.

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