EXHAUST MANIFOLD [SKYACTIV-G 2.0]

2016 – MX-5 – Engine

Discharges exhaust gas from each cylinder efficiently.
4-2-1 type exhaust pipes have been adopted which prevent exhaust gas from flowing into other cylinders during an overlap condition and reduces residual gas in each cylinder. As a result, the charging efficiency is enhanced because a larger amount of fresh air can be introduced into the cylinders. In addition, engine knock is prevented by suppressing temperature increase in the cylinders.

The exhaust manifold is located on the side of the engine. In addition, it is integrated with the catalytic converter (WU-TWC).

Residual gas occurrence mechanism

When exhaust gas is exhausted from the cylinder, a pressure wave occurs inside the exhaust pipe.
The pressure wave reaches each cylinder and the high-temperature exhaust gas in the exhaust manifold is pushed back into the cylinder, which is in overlap.
The exhaust valve closes and the exhaust gas pushed back into the cylinder remains in the cylinder (Residual gas increases the temperature inside the cylinder and causes engine knocking).

Advantages of 4-2-1 exhaust pipes

Suppresses engine knocking by reducing the residual gas and preventing the temperature inside the cylinder from increasing. A high compression ratio has been achieved by suppressing engine knocking.
With conventional short exhaust pipes, the pressure wave which occurs during the exhaust stroke of the No. 3 cylinder reaches the No.1 cylinder, which is in overlap. Because the exhaust valve of the No.1 cylinder is open while in overlap, high-temperature exhaust gas in the exhaust manifold is pushed back into the No.1 cylinder. With the 4-2-1 exhaust pipes, it takes time for the pressure wave to reach each cylinder because the length of the pipes is long. When the pressure wave occurring from the No.3 cylinder reaches the No.1 cylinder, the exhaust valve has already been closed, therefore the amount of exhaust gas which is pushed backed at almost all engine speeds is reduced.