The Gulfstream IV is an improved, larger, longer-ranging and more advanced development of the earlier II and III models. The most significant improvements with this model are its Rolls Royce Tay turbofans which offer a fuel burn reduction despite their higher thrust output than that in the previous Spey engines (the IV continues a long partnership between Gulfstream International Corporation and Rolls Royce dating back to when they first collaborated on developing one of America’s earliest pressurized commercial airliners). Other changes include a stretched fuselage for greater efficiency at high altitudes as well as aerodynamically strengthened wings designed specifically for increased lift at low speeds.