rod stroke ratio | The Z Club of Great Britain
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rod stroke ratio

Discussion in 'Rally & race' started by franky, Sep 17, 2017.

  1. franky

    franky
    Z Club Member

    84mm bore

    Compression distance 1.379”

    Dome height 0.035”

    0.6cc positive dome

    Intake valve pocket 0.120” deep x 12 degrees

    Exhaust pocket 0.110” deep x 12 degrees.



    I'm using an l24 block, l28 crank, l24 length rods. The pistons were designed as a 'cheat' gives me 2627cc. Big(ger) valve e31 head. 39cc. 10.5:1 cr, 294 deg cam

    This gives me a rod/stroke ratio of about 1.68 against a 1.8ish as standard. The way I understand it this is slightly 'better'? Or have I understood wrong?
     
  2. tel240z

    tel240z
    Z Club Member

    Yes Franky this is better i use an l28 block and crank with 240z rods
     
  3. franky

    franky
    Z Club Member

    Yes, it's the pin height in these pistons as they were used to create a naughty 'cheat' engine spec
     
  4. SeanDezart

    SeanDezart
    Z Club Member
    Official Trader

    What is this - sex by numbers ?
     
  5. jonbills

    jonbills
    ZClub Administrator
    Staff Member Committee Member

    L28 rods with l28 crank have a 1.65ish ratio.
    Not much in it.
     
  6. SKiddell

    SKiddell Having a bad day

    We alter the pin height to compensate for using different rod lengths to ensure they sit at the correct height in the block yes but pistons have no influence in rod/stroke ratio.

    Could you tell me what a "naughty" cheat engine is ?
     
  7. franky

    franky
    Z Club Member

    Yes, from my understanding it'll help with the feel of the engine I want also.

    The pin height isn't at the same point as a standard piston, so for the same swept volume you'd argue that they do influence the rod/stroke ratio as you change the rod to compensate?
     
  8. SKiddell

    SKiddell Having a bad day

    Not the right way of building an engine, the bore, stroke and rod dictate the size and characteristic of the engine, so you select a stroke and bore to get a capacity, then plan a stroke/rod and bore/stroke ratio (IE what the engine is for, race, street, pulling up trees) then design the pin height to set the piston in the correct position in the bore, if your changing the rod to compensate for incorrect pin height then that's counterintuitive
     
  9. franky

    franky
    Z Club Member

    Agreed, I Just meant it does have an effect on the ratio...
     
  10. SKiddell

    SKiddell Having a bad day

    Rod 138mm
    Stroke 83mm
    Pin height 35mm
    Ratio 1.66

    Rod 138mm
    Stroke 83mm
    Pin height 1,000,000mm
    Ratio is still 1.66

    The clue is Rod/Stroke ratio, not Rod/Stroke/Pin height ratio
     
  11. franky

    franky
    Z Club Member

    :d
     

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