I'd recommend getting a turbo starter to go with the turbo flywheel.  It should bolt right on.  The flywheel assembly spins pretty fast and needs to be balanced, I wouldn't trust welding there, or at least not MY welding :)  I think starters are physically interchangeable for all turbo cars from 86 on plus RX-8s, but to be absolutely sure you could also match the series of car.  (You can probably find an RX-8 in a local junkyard).

On Thu, Jul 14, 2011 at 10:41 PM, David Leonard <wdleonard@gmail.com <mailto:wdleonard@gmail.com>> wrote:

    I finally got to the hangar and measured out my S5 turbo flywheel
    and the remains of my S5 flexplate.  The results are very
    encouraging, even as good as the possibly could be to make the swap,
    but I only had ten min at the hangar before I had to leave to pick
    up my daughter from daycare, so they are one try and slightly
    sloppy... I make no guarantees.  The height measurements of the flex
    plate were particularly suspect because, well, mine is all warped
    and broken.

    *Ring Gear Diameter* - Perfect fit.  As we suspected, same size,
    same tooth spacing.

    *Ring Gear Fore-Aft Placement* - As measured from the underside of
    the big nut. (for all further reference, aft means aft in the CAR).     The flex plate puts the aft side of the ring gear 1.290 inches from
    the front of the big nut. The flywheel puts it 0.913.  So the flex
    plate puts the ring gear (appx) 0.377 in. further aft.  This is
    actually fortuitous because it just so happens that the ring gear
    thickness is .365 ...    So all we have to do to fix the discrepancy
    is weld and extra ring gears onto to the flywheel ring gear and
    there will be teeth that the starter can reach:(bottom of the page..
    the cost $80)
    http://mazdatrix.com/flywheel.htm
    It may also be possible to fix the discrepancy by changing the
    starter... will look into that.

    *Damper Plate Placement* - On the flywheel, the mounting surface is
    proud (or aft) of the ring gear.  On the flex plate, the mounting
    surface is recessed (or forward) from the ring gear. And it all
    pretty much works out.  That position on the flywheel will vary
    somewhat depending on which flywheel you have and how much wear you
    have on the clutch slip surface. But on my (I assume well-worn)
    flywheel the placement was 0.965 while the flex plate was 0.950.     Pretty damn close and given measurement error it might me meant to
    be right on.  Or, any difference could be made up by trimming down
    the spline on the damper plate or removing or adding spacers between
    the two.

    So in my mind, a flywheel is the way to go.  Stout, easy to get,
    pick your weight, only mods seem to be drilling the mounting holes
    and welding on a second gear ring.

    --     David Leonard

    Turbo Rotary RV-6 N4VY
    http://N4VY.RotaryRoster.net
    http://RotaryRoster.net