There are lots of posts about cleaning SAI ports and useful diy adapters for soaking and blasting with air. However I could find no flow diagram for the SAI passages in the cylinder head and on to the exhaust manifold.
So I’ll try to upload 3 photos to help you understand what I think happens to Secondary Air once if reaches the top of the cylinder head. The photos are from underneath a 2001 M96 Boxster S with the exhaust manifold/catalyst removed for inspection.
There are 7 relevant holes in each cylinder head. The largest hole is approx.. 3/8” diameter and shown by the large drill bit (gently) wedged in for these photos(not for cleaning!). I presume this is a direct, straight, vertical passageway to the flanged connector on top of the cylinder head. This is how the Secondary Air arrives at the cylinder head assuming the upstream SAI system is functioning correctly.
The Secondary Air is blown down through this large passageway and then hits the exhaust manifold gasket in the area marked with a green circle on the photo of the exhaust manifold gasket.
From there pressure/air flow from the SAI pump blows the air in both directions along the serpentine shaped channel in the cylinder head. The air flow is trapped in this channel by the gasket. You can see the black exhaust stain on the gasket where I hadn’t finished cleaning it.
Then the Secondary Air is forced up into all of the 6 small(3/16”) pasageways.
After that ,you can’t see the pathway but there must be a sharp turn into the exhaust ports ,just downstream of the valves.
If you blast some compressed air into any of the 6 small passageways you should feel the air exiting via one of the 3 exhaust manifold openings.
If we can confirm the tortuous route the Secondary Air takes in the cylinder head it will be easier to clean the passageways effectively.
It is important to note that the Secondary air does not come blasting out of the 6 small diameter passageways, it goes IN to them.
Please correct this explanation to help others perform SAI port cleaning effectively.
To work back through the remainder of the Secondary Air system , toward the SAI Pump you may need to remove both inlet manifolds.
