Ported intake for E34 535i

[Bart]

What all is involved with porting the stock intake manifold for a 1990 535i?

Why is the stock configuration less than optimal?

How expensive is it to port the intake manifold?

[AllanS]

Here's a guide on head porting which may be applicable. It explains theory, process, and of course, tries to sells you stuff.

http://www.sa-motorsports.com/diyport.htm

I believe the main reason to port it is so the ends match up properly. Right now, there's going to be material at the exit of manifold/entrance to cylinder head that doesn't match up correctly with the intake manifold gaskets, and thus creates a restriction or disruption to airflow. By porting the manifold, you would be removing material so that it mates up to the intake gasket and cylinder head as accurately as possible.

[632 Regal]

right, the purpose is to port match the gasket ends of the intake to head. It is better to leave a little material on the intake making the hole smaller than the head than to get it exact and after bolting it on have a step down as the air goes into the head. Plus it helps with reversion to leave a small step (within 1/16th) on the intake with longer duration cams. Whatever you do be careful or you will have to either get another intake or epoxy the mess ups and try again. Either way it's always fun the first few times port matching.