what size punch & tap & fitting for vortech charger install

where to buy

 

3/8" NPT tap for a 93 Z28. Make the hole 9/16" the best you can. I used a rather small punch to start the hole and gradually worked my way up to larger tools I had laying around like a rather large screw driver with a nice tapered head to expand the hole. I gauged the hole size with a 1/2" drill bit to see when I was close. I tapped it with the hole really only 1/2". You can get the tap and punch at the local hardware store for like $5-$10/piece if I remember right. You'll probably only use the tap once but it's not that much. See page 10 of the following link:
vortech installation manual

I had my pan off the block at the time (since I was rebuilding the motor on a stand anyway).