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Any differences between 400 SBC and 454 BBC flexplates?

Discussion in 'The Garage' started by thatK30guy, Nov 20, 2005.

  1. thatK30guy

    thatK30guy 1 ton status Premium Member

    Jan 12, 2001
    Likes Received:
    I got a new one for my 454, but it does not have the dual bolt pattern for the convertor. All 6 holes are the same pattern and none of them align to the holes on the convertor.

    A friend brought a flexplate that came off a 400. It has the external weight like the BBC, but looks slightly different. This plate has the correct pattern to mate to the convertor.

    Question is; can the external balanced 400 flexplate work behind the 454 without problems? Or are there some differences between the two?
  2. Jimbo*

    Jimbo* 1/2 ton status

    Mar 8, 2005
    Likes Received:
    roswell, new mexico
    No, they don't interchange. They are different part numbers, and the counter weights are different(weights). 400SB is, if I remember correctly, 1oz lighter than 454BB.
  3. diesel4me

    diesel4me 1 ton status Premium Member

    Jul 24, 2003
    Likes Received:
    Jimbo's right..

    I have used ones for both hanging on a nail in my shop--they are slightly different,the 454 has 2 additional small weights tacked over the bigger one..both of the ones I have are a bit wore out in the teeth department..I don't know why I save some of the stuff I do! :confused: --but I guess they would work in a pinch..both of them have the "dual" bolt pattern..

    You are missing one of the bolt patterns??---thats weird,because if they drilled all six holes,that means it SHOULD have both the TH350 and the TH400 patterns in it..unless maybe its a weird one for one of those HD 6 bolt converters,which I've only seen once in a van that had a 292 six..or in diesels..

    You can swap TH350 and TH400 converters ,to get the right bolt pattern,if that helps you.. :crazy:

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