The Gulfstream IV-SP is a significantly improved, larger, longer range and more advanced development of the earlier II and III. The most significant improvement with the G-IV over our previous models are Rolls Royce Tay turbofans that bring fuel burn improvements despite their higher thrust output than Speys found on both models (Gulfstream I continues an established partnership between Gulfstream planes & Rolls Royce). Other changes include a stretched fuselage as well as aerodynamics enhancements to make it structurally sounder.