This particular tach reads the pulses from the distributor. It is clearly marked on the box it comes in, "for V-8 use only". And the phone guy still told me it would work for a 6. And it WAS Classic Parts of America, formerly Chevy Duty. Someone will correct me if I'm wrong, but I believe it is 3 pulses for every RPM for a 6, and 4 pulses for every RPM for a V-8. I have the Dolphin gauges now, and this brand has a switch on the back of the tach for a 4, 6, or 8 cylinder distributor so that it will read the distributor accordingly.
