Based on a CN Ⅴ gasoline engine

two integrated exhaust manifolds of Type 4-1 and 4-2-1 were designed

and the effect of these two different structures on engine dynamics was studied by one dimensional simulation. Results show that with the integrated exhaust manifold

the engine torque does not change obviously at the speed greater than 1600 r/min

with a fluctuation of 2% relative to the original exhaust manifold. However

at the speed less than 1600 r/min

the engine torque drops significantly. Especially for the use of Type 4-1 exhaust manifold

the engine torque drops by 11.1 N·m at the speed of 1200 r/min

which is more than 6% torque of using original exhaust manifold. Therefore

the reason for the reduction of low speed torque caused by the integrated exhaust manifold was studied at the speed of 1200 r/min. Results show that the use of integrated exhaust manifold changes the intake pressure before the turbocharger

which affects the turbocharger efficiency. At the same time

an increase in the exhaust back pressure during the overlap of intake and exhaust valves causes an increase in the exhaust reflux and residual gas in the cylinder

thus reducing the inflation coefficient of the engine. The final test indicates that the use of Type 4-1 integrated exhaust manifold is indeed to make the low speed torque lower than with the original exhaust manifold

which verifies the accuracy of the simulation calculation.