I had always wondered about all the passages in my intake manifold, so I decided to figure it out once and for all. So I used an air compressor and some duct tape to firure out which passages were connected where. I was surprised to discover 5 totally separate passages!

I took some pictures and marked them up so I could show you guys what I found:

http://z28.reanimator.org/stuff/intake/front.jpg
This one's kinda obvious. Most people have seen the front of the intake before.
Inside, the PCV IN hole just connects to the IDLE AIR passage. But they don't mix with the MAIN PLENUM.

http://z28.reanimator.org/stuff/intake/bottom.jpg
This pic shows the IDLE AIR passges. Also there's a little slot that connects to the PCV VALVE. This draws the blowby gasses from the lifter valley.

http://z28.reanimator.org/stuff/intake/dile_air.jpg
They feed directly to each of the intake runners.

http://z28.reanimator.org/stuff/intake/dile_air2.jpg
The idle air travels through very narrow holes into the runners.

http://z28.reanimator.org/stuff/intake/egr.jpg
The EGR uses two passages. One just connects the EGR tube (the one from the exhaust header) to the EGR valve. Maybe that tube gets too hot to connect dirctly to the EGR valve.
The other passge connects the EGR valve to the front of the intake!

http://z28.reanimator.org/stuff/intake/egr2.jpg
The EGR gasses travel from the back to the front, using a passage that runs inside the hump on the center of the MAIN PLENUM floor.

http://z28.reanimator.org/stuff/intake/egrtoplenum.jpg
The EGR gasses come out of the two small holes behind the throttle body opening and mix with the MAIN PLENUM.

http://z28.reanimator.org/stuff/intake/side.jpg
On the driver's side there are 4 holes which lead to 3 different places.


edit: added the last pic.

 

Nice write-up! The more you know the more you're likely to mod...

 

wild!

guess I never realized how many separate passages there are.

 

here is blue print/ drawing of the heads while were at it

i'll upload some more later of other views and LS1 heads