The 7.3 uses oil pressure from the high pressure pump to activate the intensifier piston in the injector. A stock injector will have a 7:1 ratio so with 3000 psi of oil you have 21,000 psi of fuel coming out the tips. All of this happens inside the injector body. Fuel pressure between 40-70 psi is all that is needed to feed the injector. Hope that helps.