promotes the mixture of air and fuel
reduces intake noise
cools the intake air to a suitable temperature
distributes intake air equally to the cylinders
one
two
four
eight
regulates the intake air flow rate
reduces the intake air noise
enhances intake efficiency
regulates the intake air temperature
optimization of exhaust efficiency
reduction of exhaust noise
reduction of nitrogen oxide in the exhaust gases
reduction of the exhaust gas volume
recirculating exhaust
using catalytic converter
using some additives in the fuel
none of these