know of a FACTORY Spec of Inch Of Vac for 70s up on the 442 (455)

Have looked at every piece of FACTORY Lit i can find NOTHING.

 

Generally you should expect between 17”Hg - 21”Hg with stock cam. Reading should be rock steady.

 

6C-7 of your Chassis Service Manual. Took me longer to type this than to find it.

 

The W30 4speed made less vacuum than that because of special cam. That’s why you could not get AC or power brakes on a 4 speed w-30 on 1970 anyway. Vacuum gauges are cheap. It’s interesting to check you engine to see what your vacuum reading really is. More radical cams the vacuum needle will bounce a little. More street type cams will show a steady reading.

 

this @ idle^^^^^^^^^^^^