nah its when you decrease the pressure you increase the velocity, like when you put your finger at the end of a hose, u create a restriction, but he same amount of water that enters the restriction must leave it, thus increasing its velocity. for example and ill make it easy for u to understand. The gas or water in this case has a given amount of energy (kinetic energy and static pressure). so we will just say 50 kinetic energey and 50 static energy entering the hose or exhuast pipe, when the water comes to the constriction (your finger) or when it comes to the bend in the pipe which is not as wide as the rest of the pipe, some of the water or gas pressure is sacrificed into kinetic energy. thus the total energy content remains unchanged. The water/gas velocity increases and its pressure decreases. Thats why the water sprays out when u create a constriction.. moreover thats why the gas at the bend that is smaller in diameter increaes it veloicty.