Minimum Vacuum Pressure for Dual Diaphragm

[GNONYX]

Hi All,
I don't have no problem with the PowerMaster, but I want to know what is the minimum vacuum pressure is needed for a 87 Monte Carlo Vacuum Brake Booster?

 

[GNONYX]

I have read some are using 87-87 Monte Carlo Dual Diaphragm Brake Booster to replace the PowerMaster.
According to this Monte Carlo site the admin. wrote:
"For the brake booster to operate at peak performance, engine vacuum should be ideally at 18 inches"
http://www.montecarloss.com/community/ubbthreads.php?ubb=showflat&Number=757283#Post757283
I don't know what everyone vacuum is, but on my TR I have 18psi.
With that being said, can I still use the Monte Carlo Dual Diaphragm Brake Booster?
Also I have read if you have some mods done on your engine the vacuum could be less than 18 psi, is this a true statement?