Vacuum port question???

[Keitha]

What is the difference between Ported Vacuum and Manifold Vacuum?
Would one be more appropriate for the MAP sensor on a TBI unit than the other?

thanks,

 

[4X4HIGH]

Manifold vacuum is full vacuum at idle and ported vacuum is vacuum above an idle. Typically anything above the throttle plates is ported vacuum and anything below the throttle plates is manifold vacuum.

 

[eagle mark]

and the correct spot for a MAP sensor is the back of the TBI between the fuel ports. This is a direct manifold vacuum port.

 

[Keitha]

I should have added that I am running the Holley TBI (have been for a few years). I was reading today that the rear vacuum port on the Holley unit goes to the IAC port and leads to inaccurate MAP readings. Holley now states to run the MAP to a port on the front. The front has manifold and port vacuum. I do have an unused manifold vacuum port that I will use.

thanks for the quick replys.

 

[dyeager535]

I'll x2 the manifold vacuum for MAP sensor if you need a second opinion lol.

Ported is called "timed" by GM, as it only sees much vacuum at a (normally) fairly narrow range of throttle opening, based on where the hole/slot is cut in the venturi wall to feed it.

Edit: guess that's what I get for opening up a window and taking my time to reply