[mcc351]

On the front of the cylinder heads of my 351w, there are 3 threaded holes(each side, each cylinder). They are plugged up in the front with accessory brackets( alternator bracket, power steering pump etc.). On the back side (firewall side) they are completely unplugged (except for the grounding strap). Question is, should they be plugged? Are these holes a source of a vacuum leak?

 

[Lizer]

They are just thread bosses. They don't need to be plugged with anything.