Actual engine vacuum. Should be a vacuum tree coming out of the rear of the intake manifold that you can tap by taking a vacuum cap off of.
I think the notch is at 180?
I have a 4v balancer off the car in the shop. I can shoot a picture of the timing marks if need be and post it here. Let me know if you need it?
"Your" intake should look like this with the tree at the rear. You can see it in this pic.
Connect the vacuum gauge to that.
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