They recommend it but I have got away with NOT doing that several times with no problems at all "Water Weepage".. On the TT Engine I used Studs and the block and heads were surfaced smooth per cometic specs. I also sprayed them with copper coat before install and torqued the heads to 105lbs using ARP Lube. I torqued them in about 8 gradual steps. That was a flipping work out!!