I'm designing my own speedometer. just wondering how the speedometer works in an 86 t/a with 4-barrel carb. if it is cable driven or uses vss. I want to know where the signal is picked up electrically before it goes to the bufferbox/ecm. I need to how many pulses per mile.

An 86 Firebird should have a VSS driven speedometer, something like 4000 pulses/mile.