Obviously the word is that the PI intake manifolds add substantial HP when installed onto NPI heads/block combination. With all of the problem manifolds that Ford has installed on the 96-98 4.6 motors, seems that Ford (or someone else) would create a replacement manifold available with the PI design and fitted to install right onto the NPI motor for those that are just looking to replace either the leaky manifolds or to add a little HP without having to go into replacing heads or spending excessive money for an 'installation kit'.