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  1. #1
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    Default Detonation and pre-ignition: an introduction

    Stumbled onto this article and learned something new.

    https://compare.parts/torque/underst...ilure%20modes.

  2. #2
    FEP Super Member xctasy's Avatar
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    Bum= Burn.

    Pretty much A.Graham Bells 4 Stroke Performance Tunning from the 4th Edition of 2012, pages 188 and 299 to 300. Thanks for sharing. Dean Stevenson, XEC Ltd New Zealand.

    Liked..aside frpm the Bum → Burn Thang.

  3. #3
    FEP Super Member gr79's Avatar
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    [QUOTE=darkd0r;1931634]Stumbled onto this article and learned something new.

    2x Thanks for sharing. More food for thought.

    Thinking about engine tuning, did a search 'does a bigger carb need a different PCV valve?'
    Many results
    One
    idle tuning issues, oil leaks. No road test or dyno results.
    http://www.engineprofessional.com/ar...Q315_34-44.pdf
    Last edited by gr79; 11-05-2020 at 02:29 PM.

  4. #4
    FEP Super Member xctasy's Avatar
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    darkd0r

    Jack Hidely posted this. The Crank Angle Degrees verses combustion pressure in Atmospheres graph.




    A. Graham Bell describes it very well, right to the degree, while the Original Author Shahin Fard is general, (and Sam Borgman, the Technical Engineer for Life Racing).

    The article doesn't phase it in with fuel delivery differences between carb, throttle body injection, bank and sequential injection, or pulse tuned Independent throttle body Carbs.

    A.G.Bells 4th Edition Haynes version of Four Stroke Performance Tuning.





    Readings in psi on the y axis would be helpful because Turbo and Super charged engines read over 1500 psi or 100 atmosphere before cylinder sleeve or bore wall collapse.


    Way back from this graph is where Fords EEC and some MCU computers tried to optimize tune using:-
    1. BMAP
    2. MAP/MAF/VAM
    3. ECT (water temp)
    4. Knock Sensors .
    5. O2 sensors
    6. throttle position.
    and 7. Administered timing

    are used to assess Charge dilution, humidity, PCV, EGR, AIR, and all that stuff is done on Fords factory dyno sessions. Preignition and Detonation can set in very early with good chamber filling, and the old school air fuel control by VOTM/Throttle Stop Positioners and Throttle kickers and Dashpots were used before ISC/IAC valves based on vehicle speed.

    Distrovac was first in 1969, a 16 degree at idle advance engine with 34 degrees advance at 4000 rpm, that used the system as a way to get the real 352 hp gross rating 11:1 compression Boss 302 through California's Emission tests without holing a piston, based on a VR sensor later used for cruise control, and speedos.
    By 1981, the same kind of canted valve head was in duty with 7.9:1 compression on the 138 hp net 351M engine, which was was dialed in at 9 degrees at idle and 50 degrees on trailing throttle, or 44 degrees at 3500 rpm. And it used 100% electronic mapping of the Variable Venturi Feedback carb as one of the many crutches to make it pass the emissions without creating black death.

    Back to gr79


    We only see the characteristics from the supplier on PCV and EGR on CFM blowby, and AIR application in pounds per hour.

    Motorcraft gave some details way back on the three types used on 4.9 liter Bix Sixes and 302 V8s.

    Dyno tests are done a zero humidity and corrected to 59 to 77 degree temperatures and the air pressures anywhere from 29 to 31 in Hg. They then do field hot and cold running with data logging once they have the federal emissions certification roughed out. So a PCV can certainly change things. What a Weber Holley 2 bbl needs is different to what a Holley 2300 or 2305 needs. Holley's classic 2300/2305 350 and 500s are always easier to get clean emissions, but fuel consumption suffers vadly unless the power valves and well tubes and idle, transfer and wide open throttle calibrations are changed. Ford spent more money on detonation resistance with the 2300 OHC than on carbs. They downgraded to a Carter 1 bbl on OHCs and a Holley 6149-6153 on the 2.3 OHV because at 72 to 88 hp, a bigger carb wasn't going to fix fuel economy or cylinder filling.

    Its only the performance guys like Esslinger or Racer Walsh who worked on 2 and 4bbl carbs and Ford spent most of its time making sure any 2.3 or 2.5 OHV or OHC met the fleet average MPG targets on 87 octane gas. The OHC Lima PCV system is designed for a far more " finickity" Weber Holley. A Holley 2305 wont need half the effort Ford put into the 1975 to 1982 2 bbl 2.3s. The intake manifold port size downgrade was non carb turbo.

    The Lima is one of the most detonation prone engines, and the solutions to getting better performance and economy was better dual plug ignition and port EFi and a huge reduction in wide open throttle advance and a part throttle advance increase. The increase in capacity to 2.5 liters didn't hurt fuel consumption. This is 3D ignition mapping.

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