older 5S-FEs without swapping cylinder heads. The 1997-99 Camry 5S-FE continued with the air-assisted, 250 cc injectors. The Camry 5S-FE also had a factory 4-to-1 exhaust design - in Federal form, it had no pre-catalyst, although the California version did replace the collector design of the Federal version with a warm-up pre-catalyst for reduced cold start emissions. For 2000 Toyota removed the air-assisted injectors and moved to superfine atomization (~50 micrometers), 12-hole, 235 cc injectors made by Denso. They are of a different design, and required a change in the cylinder head casting. For 2001 Toyota started fitting factory MLS (multi-layer steel) head gaskets and other metal gaskets layered with Viton to engines, including the 5S-FE. MLS head gaskets require cylinder head and cylinder block resurfacing on older engines to ensure proper sealing; consequently, the MLS head gasket did not supersede the old composite head gasket. The 1994 through 1999 Celica 5S-FE was not updated with these changes, and continued to use a distributor and the older electronic control system and injectors. The 5S-FE has a 9.5:1 compression ratio. Applications ST184 (5th generation US Celica GT and GT-S, Australian Celica SX) ST204 (6th generation US Celica GT) SW21 (2nd generation US MR2 N/A) SXV10 (Camry 1992–96) SXV20 (Camry 1997–01) 5S-FNE Essentially a CNG version of the 5S-FE. This engine was fitted to the XV20 Camry in California to fleet customers in 1999. See also List of Toyota engines References S World Sportscar Championship engines Straight-four engines