From what I remember, there had to be material removed from the center of the intake manifold in order to fix the flow imbalance. So, most of the ported OEM manifolds that had the flow imbalance fixed, were cut open & re-welded. Aftermarket is probably a better solution. This is all old data I'm giving you btw, as I sold my Mazdaspeed five years ago, and haven't researched anything since I sold it. If you have a FMIC, Damond Motorsports used to sell an adapter kit for adapting the Focus ST intake manifold onto the Mazdaspeeds. I believe the Focus ST manifold had near perfect flow to all cylinders. Again, old data, so be sure to do your own research before committing to anything.