Flex-plate questions....

[b5blue]

  Why does it need to flex? Why 4 tiny bolts holding it to the convertor? I get that they are spaced fairly far out from the crank so leverage is "in there favor" but with all the beef elsewhere in the drive train that thin Flex plate and tiny bolts just seem like a weak point. 
  I see much stronger looking Flex Plates for sale but then they would not flex, right?

  I have never had any problems other than the bolts loosening up some one time years ago but soon I'm getting the 727 rebuilt and switching to a new 145K Mopar Performance convertor so I'm wondering what's the best Flex Plate to use? Mine is stock right now and I have new convertor bolts to install at that time.

[ws23rt]

The flex plate acts as a spring (shock absorber) to absorb axial movement of the torque converter and the crank shaft.
Also under high rpm the converter will swell up. (The outside diameter will increase).
The bolted side of the converter is stiffer than the other and the swelling will cause it to dish.
The flex plate will allow for that movement and hold position.
If the flex plate were to not flex it would force the convertor swelling to be on one side and put stress on the welds (cracking).

IMO if the torque convertor were to be manufactured to higher tolerances with higher grade materials It may not need a connection that flexes as much.
However everything flexes and if a force that flexes something is held fast that force will aggravate something else. The parts need room to move.
Another item that is of value here is keeping the rotating weight as low as possible.

[John_Kunkel]

The converter materials/tolerance is only part of the need for a flexplate, the difference between the crankshaft centerline and the transmission centerline will vary because of production tolerances and the flexible coupling will allow for this misalignment. Severe misalignment will result in repeated flexplate failures due to cracks.

Standard transmission bellhousings are align-bored with the engine block to maintain perfect centers.

[b5blue]

Thanks guys!