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Thread: SP450 vs SP450A

  1. #1

    Default SP450 vs SP450A

    I replaced the plugs and wires on one of my cars last night with motorcraft parts.
    The plugs I got were SP450.
    Anyone know the difference between SP450 and SP450A?

    The change solved my miss under load problem.

    Sent from my iPhone using Tapatalk

  2. #2


    SP450 is just the older version of the SP450A, the long part number for the SP450 is ASF42C, the long number for the SP450A is ASF42CA, both are copper core the heat range and the seat type are the same. The usual reason that Ford will add an A to the motorcraft number is a switch in suppliers, example went from an Autolite to NGK manufacturer, Ford will superseded the part number, usually adding an A on the end of the part number.

  3. #3


    The long part number on the spark plug from Motorcraft will tell you quite a bit about the plug itself, for example ASF-42-C breaks down with the ASF is the seat and thread size ASF is a 14MM tapered seat, BSF is an 18mm tapered seat, AGSP is a 14mm gasket style seat. The 42 is the heat range a cooler plug would be a 32, 22 and so forth, a 44 would be the same heat range with an extended tip. The suffix of a C would be a copper core, P would be a Platinum, and a FM would be a fine wire platinum and so forth. I like to use the long number but the short number causes much less confusion and your chance of handing out the wrong plug are a lot less.

  4. #4


    Awesome thanks!

    Sent from my iPhone using Tapatalk

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