Got a torch? heat up the exhaust housing and use a leather/hide mallet. When I opened one up it was seriously stubborn, in the end I used a large hammer to hit a piece of solid metal bar on the exhaust housing.
Put it in a small workbench if you have one, with the exhaust housing closest the floor hanging under the bench and clamp the inlet housing in the bench, then when you hit it, it can drop freely onto the floor, I would suggest something a little padded underneath!