Split Cylinder Bore

Discussion in 'Technical' started by BLACK BEAST, Oct 6, 2016.

  1. BLACK BEAST

    BLACK BEAST SLICKTOP TT R-SPEC

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    [​IMG]

    Thought I had a blown headgasket but it seems no 3 cylinder bore decided to crack.

    Had a look at my info on the blocks I've had x-rayed for bore wall thickness but cant remember which blocks which.

    From my results
    A VG block can vary from as thin as 140 thou (3.5mm) up to 330 thou (8.3mm).
    Add boring and 20 years of potential rust and they can get pretty thin .

    Everything else from chambers ,pistons ,bearings etc are in excellent condition which is good to know at this power level .

    Cylinder 3 on one of my sheets is not too thick around the 160 thou before machining so with everything else being in good shape can only put it down to that if that's he block


    new block is at machine shop getting done

    must be all this cylinder pressure :p


    .
     
  2. MagicMike

    MagicMike Moderator Staff Member

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    I dont want to play this game anymore lol depressing bastard
     
  3. Anti

    Anti 14.7 x 14.7 = 44.1

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    **** me
     
  4. lcram

    lcram O'le Fella

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    had this on my L28 6cyl, machine shop fitted a new sleeve and bored it to suit , so far it is working well
     
  5. Cheddle

    Cheddle New Member

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    ^

    I lol'ed
     
  6. rob260

    rob260 Moderator Staff Member

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    About 636psi if the equations are correct
     
  7. BLACK BEAST

    BLACK BEAST SLICKTOP TT R-SPEC

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    Sounds like alot
     
  8. rob260

    rob260 Moderator Staff Member

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    It does, but if it's making 3x the torque of a stock motor it stands to reason that cylinder pressure would be 3x that of a stock car -it's all just conjecture and text books though, I don't think it's possible to measure
     
  9. kickerzx

    kickerzx Member

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  10. BLACK BEAST

    BLACK BEAST SLICKTOP TT R-SPEC

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    Just have to wait til the head lifts and then you know its time upgrade :)
     
  11. rob260

    rob260 Moderator Staff Member

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  12. kickerzx

    kickerzx Member

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    :) I guess so
     
  13. Anti

    Anti 14.7 x 14.7 = 44.1

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    I had to do this for an assignment last semester

    came out to a lot more than 636
     
  14. BLACK BEAST

    BLACK BEAST SLICKTOP TT R-SPEC

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    Just found this post z related

    Figures seem right that Rob indicated

    This is for 750ftlbs at crankshaft
    Im 750ftlbs at the wheels (880ftlbs crankshaft from dyno coversion)

    600psi on an 87mm (9.215 sq/in) piston is 5529 lbs of force. On an 83mm stroke that will produce 753ft/lbs of torque at the crankshaft.

    Now if you increase the bore to 88mm and leave everything else the same, when the cylinder is at 600psi pushing on an 88mm piston (9.4270 sq/in), it generates a force of 5656.2lbs. On an 83mm stroke that will produce 770ft/lbs of torque at the crankshaft.

    This has a difference of 17ft/lbs of torque, but typically going from a stock 87mm piston to a lighter forged 88mm piston reduces significant weight from the rotating assembly and there will likely be more of a gain seen from that fact alone than from the bore size increase.

    There is also the fact that when you bore out the cylinder for the larger piston, you are increasing the displacement of the engine slightly. This means more burnable material will be available to make power from. In the example above, my calculations were leaving everything the same except for the bore size to demonstrate what the direct, immediate difference is when you simply go to a bigger piston, but there are a lot of other variables like less weight and greater displacement that change to the advantage of making more power.

    We have wiseco forged pistons
     
    Last edited: Oct 7, 2016
  15. Anti

    Anti 14.7 x 14.7 = 44.1

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    636 psi at what part of the 4 stroke cycle? The figure I calculated calculated while back was for immediately upon plug ignition before the piston descended (no volume increase).
     
  16. East Coast Z

    East Coast Z Well-Known Member

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    The general consensus with the cause of cracked blocks seems to be overheating issues & then the possibility of thin cylinder walls.

    How far over bored is the block?

    What caused the scoring in the bores?
    It is clearly visible against the cross hatching.

    The block is now junk, might as well section it & see how thick the material is in the damaged area.
     
  17. ProckyZ89

    ProckyZ89 Senior Member

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    Jesus ...
    Why now!! Just when I was wanting to do something similar lol...

    Although I do have .5mm less piston than you :p

    Hopefully that translates into luck lol
     
  18. BLACK BEAST

    BLACK BEAST SLICKTOP TT R-SPEC

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    88mm

    Theres no over heating ,runs cool... hottest I've seen engine at continuous WOT is water 90 and oil under 100 ,quickly comes down when you back off.
    chambers and pistons are excellent no signs of excessive heat .

    Every bore has those scores on either side (piston/rod pivot)
    Piston and rods are getting hammered down with extreme force so we determined that might be expected .. how many 700rwhp Z's have we seen pulled apart to compare?

    Was going to do that to see how the thick the bores actually are

    .
     
  19. 90TTZ

    90TTZ Back From The Dead

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    How many split bores have you seen with these blocks? My 2 cents worth is you were just plain unlucky. Fatigued could have been a contributor but I think the grain structure was compromised during casting will be the likely cause here. 1 mm oversize for these blocks is not excessive.
     
  20. stumagoo

    stumagoo Active Member

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    I have had 1, got it like that so I dont know the cause but I suspect its been overheated (Was #5 cylinder). also was original pistons and is my backup engine. (has good compression after a dose of chemiweld) as stated is a back up engine although I doubt I will ever need it. also has several new parts like oil pump and water pump, again the engine that I have now is also like this so probably never need to scavange them off either.
     

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