Manifold Vaccum - 390 V8

[69bsbamx]

I was checking the manifold vacuum to the transmission vacuum modulator with a vacuum tester. At idle speed, the manifold produces 17" vacuum and at higher RPM's, about 21". Does anyone know if this range is within spec?
Only thing I could find in the TSM about vacuum is that the modulator rod should retract fully at 18" vacuum. Car is a 69 AMX, 390 ci. Thanks in advance.

[donsjave]

Your 17 is actually really good for the engine that you have. My 390 reads right at 15, so I guess you could knock yourself out. I have seen engines as low as 10-12 running without any problems (at idle). My guess is that anything above about 10 is within specs depending upon your elevation. I am sitting at 5600 feet.