Since modern diesels often have a throttle, EGR can reduce the need for throttling eliminating losses in the same way that it does for SI engines. Reduced throttling also reduces the problem with engine oil being sucked past the piston rings into the cylinder causing carbon deposits there. Exhaust gas—largely nitrogen, carbon dioxide, and water vapor—has a higher specific heat than air, so it still serves to lower peak combustion temperatures. However, adding EGR to a diesel reduces the specific heat ratio of the combustion gases in the power stroke. This reduces the amount of power that can be extracted by the piston. EGR also tends to reduce the amount of fuel burned in the power stroke. This is evident by the increase in particulate emissions that corresponds to an increase in EGR.