Just had DNA 4 to 1 header installed and noticed the mechanic did not put 02 sencer instaled,I did put a high flow cat in and am not sure if tune is nessesary.1995 gen one v-tec1.6 sohc.

 

You won't get much difference without a tune. The car will pretty much run as close to stock as possible even with the new parts if you don't tune it.

As it is, you will only see a little extra with the parts. There isn't a whole lot extra in these motors without going forced induction.