The Gulfstream GIV and GIV-SP is a significantly improved, larger, longer-range, and advanced development of the earlier GII and GIII. The most significant improvement with the GIV and GIV-SP over the earlier Gulfstream models is the Rolls-Royce Tay engines, which bring significant fuel burn and noise emission improvements despite their higher thrust output than the GII and GIII Spey engines. As of January 2014, the Gulfstream GIV-SP market is comprised of 100% pre-owned. The percentage for sale is 10.8% with 88% under an exclusive broker agreement and the average days on the market are 376 days. The improved Gulfstream GIV-SP (SP representing Special Performance), with higher payload and landing weights and improved payload range performance, replaced the GIV from September 1992, (there is, however, an ASC190 that allows an owner/operator to upgrade a GIV to a GIV-SP). Production on the Gulfstream GIV-SP started in 1992 and ended in 2002.