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 brake over the wheels). See also Jake brake. Compression brakes, a form of engine brakes, produce greater noise pollution than exhaust brakes. For this reason, some vehicle original equipment manufacturers prefer to use exhaust brakes despite their lower braking power. Combining compression braking with exhaust braking can increase effectiveness without being as loud as compression brakes. Numerous cities, municipalities, states, and provinces ban the use of unmuffled compression brakes. Most exhaust brakes in the commercial market are protected by patents by companies such as GT Emissions Systems. The butterfly valve made up of acrylic material made in the circular shape, having