I have changed over to MAP on my 88 and I don't want to tap the plenum after looking at it more carefully. So what I want to do is "y" the vacuum port to the fuel pressure regulator and feed it to the MAP sensor; but to minimize any vacuum fluctuations I would like to replace the small barb that goes to the FPR with a larger barb. I was thinking a barb similar to or even bigger than the barb that feeds the rest of the vacuum lines in the car would work well. Does anyone know where I can find a vacuum barb that will screw into the plenum that is larger?

Why not connect the MAP to it's own dedicated port and Y the reg off the HVAC line coming from the other port?

Take the fitting to a engineering or plumbing supply shop.
They usually have a range of brass fittings of a certain thread type but for varying hose sizes.

Here's an idea:



The tooling hole for the plenum is just about the size for a 1/8NPT fitting (it's slightly bigger than the recommended tap drill size, but I had no issues with getting good threads).

Make a vacuum passage into the plenum with an 1/8" diameter drill in the bottom of the tooling hole (it's already pointed so you'll get a nice on-center hole), thread the tooling hole with a 1/8NPT tap and install your barb fitting.

(The photo shows a vacuum source for a vacuum gauge).