Manifold vacuum under real world driving and decel, Anyone have data on this? Options

[emerygt350]

After pbanders alerted me to the error in the decel diagrams, and I hooked the darn thing up correctly, I have been wondering what the actual vacuum while driving looks like for others.

I have a glowshift vacuum gauge on the dash (from tuning the MPS) and have been watching the max vacuum on decel, idle, cruise etc.

On a hot engine at 900 rpm idle I pull 17ish pounds. On decel 23ish pounds.

Hooked up my vacuum pump to the decel valve while idling and gave it some vacuum. No change in idle till 20ish, then increasing RPM from 20 to 28 pounds.

Bench testing the decel showed opening at 18 lbs.

I can't imagine many of you have a vacuum gauge on the dash but perhaps the bluetooth 123 records that kind of stuff?

73 2.0 djet.

[Van B]

Decel valve has a bit of a progression to it. That progressive opening is over a shorter span as you tighten it up more due to an aging valve spring.

I have a NOS and my original and the difference between starting to open and full open is 2 in-hg on the old one and 3 in-hg on the new one with both set to start opening at 20 in-hg. It’s also easy to predict the difference because the old one needs more turns in to resist until 20”.

I would say your valve is probably set to start opening at 18 and is fully open by 20.