Abstract: An engine with an auxiliary airflow booster is installed to an exhausting tube at an exhausting gate of the exhausting head of a cylinder. The auxiliary airflow booster is a hollow body. An inner wall of the auxiliary airflow booster is formed with a narrowing portion which has two opposite tapered surfaces so as to have a front via hole and a rear via hole. The front via hole has a front tapered portion and the rear via hole has a rear tapered portion. An inner diameter of the front via hole is smaller than that of the rear via hole. Since the inner diameter of the rear via hole is larger than that of the front via hole, the rear via hole expands the diameter of the body. By above structure, the exhausting speed of waste gas is increased so that more fresh air is sucked into the cylinder.