It’s not T’d actually. The stock MAP sensor is normally mounted on the throttle body, where vacuum input is accessed via a small port on the side of the throttle body.
I mounted the MAP sensor on the firewall (port facing up) and ran a short (3-4 in long) line directly into the vacuum manifold. Datalog shows that readings are within the OEM spec 0-30inHg.
The vacuum routing is like this:
Manifold has 5 ports and an exit port
Port 1 - MAP sensor
Port 2 - to runners 3 and 4
Port 3 - plugged, not in use
Port 4 - to runners 1 and 2
Port 5 - to FPR hose fitting
exit port - to brake booster checkvalve