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Thread: 890-250 Distributor Compatabilty with C950

  1. #1

    Default 890-250 Distributor Compatabilty with C950

    Just purchased a Holley new old stock 890-250 billet distributor off eBay for my Ford twin turbo project. Without any instructions or documentation, I tried my best to find something on it, but cannot find any information on the internet about this distributor. My question is, it seems to have a proximity sensor that screws in the bottom of the housing, and seems to be more advanced than a typical magnetic pickup or Hall-Effect distributor. I know how to make the changes in the C950 to switch between magnetic pickup and Hall-Effect distributors, but I'm not sure if this will even work with an older C950. Can anyone shed some light on what the 890-250 is and tips to make it work with the C950. Thanks.

  2. #2
    Join Date
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    Quote Originally Posted by cosmo66 View Post
    I know how to make the changes in the C950 to switch between magnetic pickup and Hall-Effect distributors, but I'm not sure if this will even work with an older C950.
    Hall-Effect: 3-wire, square wave signal (digital), pulse generation
    VR Magnetic: 2-wire, sine wave signal (inductive), voltage generation
    http://www.electronicproducts.com/El...g_for_you.aspx (Hall-Effect vs VR Magnetic)

    The more robust Hall-Effect sensors are preferred because they're not susceptible to EMI/RFI interference/noise,
    and their digital square-wave signal strength is consistent, regardless of RPM (unlike the VR magnetic sine-wave).
    Also, the magnetic VR signal is weaker at cranking speeds.

    Excerpt from Holley EFI manual:
    NOTE - It is not advised to use a magnetic pickup distributor to directly feed the magnetic trigger input of the ECU. If the
    magnetic pickup distributor is connected to the ECU via the inductive pickup trigger wires, the pickup/rotor/cap phasing
    must be corrected. This operation may require a phaseable cap or rotor or possibly machining to the distributor and is
    therefore beyond the scope of most users. Even with the phasing corrected, the electrical noise inside the cap
    (due to the high voltage cap & rotor terminals) may be strong enough to cause electrical noise interference.
    It is advised to use a crank trigger system or a computer-controlled distributor.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  3. #3

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    Thanks Danny. So it sounds like I do have a Hall-Effect distributor. I do see that the sensor is phaseable, by how it mounts and it has a slot milled in the housing base. Looks like I made a good choice by picking this up. Do you or anyone else that can chime in, have any of the Holley sales literature for this distributor? Would like to have it, in case I need replacement parts or could pick up some additional info on the unit.

    The distributor cap & rotor are not typical off the shelf items from what I see. The rotor seems to be one that could be a Mallory, as it has an M molded in it. By the way, the rotor does not seem to pop off or lift off like other distributors (like Ford TFI or Accel/Mallory, etc.) and has no apparent mechanical hold down screws...almost seems like it was molded into the main shaft.




  4. #4
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    Quote Originally Posted by cosmo66 View Post
    So it sounds like I do have a Hall-Effect distributor.
    Yes, it sure looks like it. I had a very similar Mallory #9556704 distributor. It's now my cam sync unit:
    http://forums.holley.com/showthread....al-EFI-Upgrade (My DIS & Sequential EFI Upgrade)
    http://forums.holley.com/showthread....nk-Trigger-Kit (My Custom 60-2 Crank Trigger Kit)

    The distributor cap & rotor are not typical off the shelf items from what I see.
    The distributor cap adapter, cap (Pro Cap), rotor & plug wire retainer are Mallory Comp 9000 parts.
    http://www.carid.com/images/mallory/info/catalogue.pdf (See end of page 24.)

    By the way, the rotor does not seem to pop off or lift off like other distributors...
    It's probably just stuck on there, or its been glued on.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

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