Porting a stock turbo & inlet bell comparison
Posted: 8/29/2004
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What we are looking at here is a stock Buick turbo compressor housing (the inlet side) and the inlet bell (removable piece).

From the factory the inlet bell and the compressor housing are pretty restrictive, and there are ways to make them flow better. First off, there is an aftermarket inlet bell available. This new inlet bell deletes the vent hole that leads to the passenger side valve cover. It also has a smoother taper from the inlet to the outlet. Finally, it has a slightly larger diameter outlet, which helps us later when we port the turbo compressor housing.

As mentioned above, the inlet on the compressor housing can be ported to allow more air flow into the turbo. This can be maximized further by using a larger inlet bell. Below are before and after pictures of everything.

Pictures: (click on images to enlarge)
Turbo on the car, prior to removal & porting. Notice gap between inlet bell and compressor housing, causing a restriction to airflow into the turbo.	Turbo with compressor cover off. Nothing of significant meaning here, just most people haven't seen a turbo like this.	Here you can see the metal we'll be removing from the compressor housing.
Another shot, but with the aftermarket inlet bell. Again, notice the restriction to airflow into the turbo. This will be gone soon enough!	Here's the compressor housing after being ported. Notice the smooth transition into the housing where the wheel sits.	The finished product. The ported housing with the new inlet bell on.
Notice the provision on the stock bell (right) for the vent that goes to the passenger side valve cover. This is what everyone blocks off so not to pull oil into the turbo/intercooler. Height and outer diameter of both units are the same.	Notice smooth transition of aftermarket unit (left) compared to stock (right). You can also see the hole on the stocker for the vent.	Notice the larger outlet of the aftermarket unit (left).