Valve head measures 28.5mm, total length is 2.580" (+/-.004"). The stock valve seat will need to be replaced with a larger ARC#6148Y valve seat. Top quality stainless steel with automotive style keepers. Will fit stock 5.5mm valve guide. Use DJ-1047 retainers for 26lb springs or DJ-1046 retainers for 36lb springs. spring. DJ-1051 lash caps are recommend.