What do the gears S3 and S4 stand for on a 91 Acura Integra GS transmission and what are they used for?

Answer 1

Those are the more performance-minded shift patterns for the transmission. Your Legend's transmission has 4 gears when shifted to "D" for Drive. S3 limits the tranny to 3 gears and S4 allows using 4th gear. The big difference between Drive and the "S" gears is that both S3 and S4 settings will allow the car to stay in a lower gear a little longer. Use this to your advantage when wanting to accelerate harder (such as passing another car) or when going down inclines (use the engine's natural resistance to help you maintain a safe speed and save your brakes for when you really need them). The "S" settings will typically result in lower gas mileage. When shifted to the "S" setting, the car will always default to S3 and you have to press the S3/S4 button to get it to use 4th gear. Pressing the same button again will put you back in S3.