I just bought a 78 280z and i notice that next to the ignitiol coil there was this square this (fireball hi-6 ignition). does anyone know what is it, and what those it do. Should i leave it or take it off.

does this help my car?

It is a Crane multi-spark ignition system. It should be an improvement although since a 280Z already has electronic ignition I would think that the stock ignition would suffice.

It only helps at the lower revs IIRC. I forget the cut-off, but once you get above a certain RPM it stops the multi-spark. I see no reason to take it off if it's already installed.

Plus it has an adjustable rev limiter, good for times when your friend borrows your Z!

how do you adjust it.

There are rotary switches on the end of the unit. Settings are x 100 rpm.