Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net> Hi Luc, Without the core it's about 10kHz. I don't know what it is with the core. Cheers, Terry At 12:05 PM 1/17/2002 -0500, you wrote: >Hi Terry, > >Do you ever try to measured the resonant frequency of a GM HEI >coil with and without the core. > > >Cheers, > >Luc Benard >