[XfireZ51]

Originally Posted by Bolling

How do I tell and what are the differences? I have read where they drone quite a bit but these do not seem to drone. You can hear them at 60 or 70 but it's not a drone. I had a C6 vette with NPP and they would drone in the open position at driving speeds so I always closed them on the highway.

I have NPP on my ZR.