how big is the dish in stock smog-pistons

Discussion in 'Engine Topic' started by marx3, Jul 25, 2010.

  1. marx3

    marx3 Veteran Member

    327
    0
    Jul 11, 2008
    Denmark, Europe.
    How many cc's is the dish in the pistons, in say an 8.2:1 ( or what ever the stock low cr was in the late 70's ) 350??? I cant seem to google the answer!

    Playing with a cr-calculator ends me up guessing around 6-8 cc's??? But I also read 22 cc's somewhere once. I am confused!
     
  2. z28rod

    z28rod Veteran Member

    4,472
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    Apr 30, 2009
    hopewell junction,ny
    12cc does this sound right ???
     
  3. Damon

    Damon Veteran Member

    12,934
    17
    Nov 16, 2000
    Philly area
    Yeah, about 12cc.
     
  4. marx3

    marx3 Veteran Member

    327
    0
    Jul 11, 2008
    Denmark, Europe.
    Hmm, actually I end up around 12 with another try. Thanks!!!
     
  5. Todd80Z28

    Todd80Z28 Moderator Staff Member Lifetime Gold Member

    10,922
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    Jun 11, 2002
    Northern VA
    Not sure if they are the same dish as the Vortec truck pistons, but those list at 18cc.
    Also, to get the 8.2:1 listed for the late 2nds, I have to plug in 15cc.

    http://www.csgnetwork.com/compcalc.html
     
  6. Damon

    Damon Veteran Member

    12,934
    17
    Nov 16, 2000
    Philly area
    Last time I actually cc'ed one (a factory original, not an aftermarket one) I got 12 plus a scosh. You might call them 13 if you want, but they're definitely not 18. These were the kind that had NO 45* bevel around the outside edge of the piston face, FYI.

    Vortec motors might well be different. GM changed their pistons around quite a bit starting around 1990. They went to a low tension metric ring pack pretty much across the board, for instance. 1991-92 350s engines in many cars often got flattop even though GM didn't change the official compression ratio spec (ask anyone who's personally torn apart a factory original 91-92 L98 TPI engine). While Vortec motors (and pre-Vortec truck motors) still had dished pistons well beyond 1990 the piston design was almost certainly different than old smog-era pistons.
     
  7. Louich

    Louich Veteran Member

    2,412
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    Mar 8, 2004
    Arthur, Ontario
    i have a 92 tpi engine on the stand right now and its got flat tops.
     
  8. sooner

    sooner Veteran Member Lifetime Gold Member

    1,414
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    Mar 11, 2009
    Perry,Ok
    I agree, and the vortec pistons do appear to have a smaller dish than the smogger pistons.

    Stock vortec pistons below:
    [​IMG]

    290hp crate motor pistons:
    [​IMG]
     
  9. Todd80Z28

    Todd80Z28 Moderator Staff Member Lifetime Gold Member

    10,922
    33
    Jun 11, 2002
    Northern VA
    That is exactly what my '80 pistons look like, including that 45* bevel on the outer edge.

    EDIT: Went looking Goodwrench 350 replacement engines, turned up 12514101. Search shows-

    http://webpages.charter.net/beckracing/slvpg26.htm

    so, 13cc dish.

    BTW, what does "destroked .020" mean with regard to the piston? Is the compression height lower so that the piston sits further down the hole?
     
    Last edited: Jul 25, 2010
  10. Damon

    Damon Veteran Member

    12,934
    17
    Nov 16, 2000
    Philly area
    Correct. Cheap "rebuilder" pistons often have a shorter (further in the hole) deck height since they assume you are going to have the deck milled during the rebuild process.

    If you use them on an undecked block they will usually sit about .045" in the hole at TDC.
     

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