Gulfstream IV / SaudiaThe Gulfstream IV is a significantly improved, larger, longer ranging and advanced development of the earlier II and III. The most significant improvement with the G IV over the earlier Gulfstream models are the Rolls Royce Tay turbofans, which bring significant fuel burn and noise emission improvements despite their higher thrust output than the II and III's Speys (the IV continues a Gulfstream and Rolls Royce association that dates back to the