[Dave80GTSi]

For posterity, posting a public answer to a private inquiry.

The cat portion of the Fabspeed header measures roughly 3.5" in diameter x 3.5" long.

Compared to the OEM manifold cat which appears to be around 4" in diameter x 4" long.

So yes, the Fabspeed cat is physically a bit smaller than the OEM cat.

Thanks - DM