Saturn S series Twin Cam cylinder head had now featured a new roller-rocker setup with hydraulic tappets and roller cams replacing the conventional bucket lifter setup of the previous engine in the S series. Also introduced for the 1999 model year S-series vehicles that were sold in California was a different type of an exhaust manifold that housed an upstream catalytic converter (this converter had heated up much faster than the conventional unit, and it had also decreased exhaust emissions faster as well), and it also had provisions for an air-injection reaction system (This had injected fresh air into the exhaust to reduce
Exhaust mixer increasing thrust. The exhaust thrust from a jet engine is equal to exhaust mass flow times exhaust velocity, i.e., "Thrust = ṁv", while the energy to make that thrust is given by "Energy" = 1/2"mv". A mixer helps reduce the fastest exhaust velocities from the core of the engine, while making the average exhaust velocity faster, producing more thrust with the same energy. Mixing efficiency is defined in a number of ways, but simply, compares the actual thrust gain (due to mixing) to that of the ideal case. Annular mixers have a low pressure loss, but a low mixing efficiency.