Motorola PC 50 Mic issue

I am having trouble with Mics for a Motorola PC 50. I have some really nice headsets and the mics work great. They are motorola brand with 150 ohm mics. I have another set - military rated new 150 ohms and they are virtually worthless. What is needed for a mic? Trying to use in helmet for racecar. The bad ones were from kit for racecar. The good ones measure bit higher resistance. Is there something needed to match impedance or gain for one verses another?
thanks for the help