,
The Mazda Skyactiv gasoline engine also uses a plastic intake manifold. It, however, does not have ribs as it does not have to deal with the pressures from forced induction. Plastic is a good material for intake manifolds for a couple reasons off the top of my head. First, it has a good and smooth surface finish improving flow. Secondly, it doesn’t transfer much heat to the intake air. Lastly, I imagine it’s relatively cheap.
One of the prominent features of the Skyactiv gasoline engine is the tri-Y header. The tuning of the header improves the exhaust scavenging allowing a sky high (see what I did there…) compression ratio of 14.0:1.
Of course the other big news Skyactiv engine is the diesel. Yeah, I looked at it last year but I’m going to point out some new stuff I noticed this year. It uses what I believe is called a ‘TwoStage Serial’ turbo setup from Honeywell Turbo. The system consists of a high-pressure turbo (the smaller one) mounted down low and a low-pressure turbo (the bigger one) mounted up high. There are two small actuators and a big actuator mounted down low. At low engine speeds, all of the exhaust flow goes through both the high-pressure and low-pressure turbos. As the engine speed picks up, that big actuator controls a valve which starts to bypass some of the exhaust gas around the high-pressure turbo straight to the low-pressure turbo. At high engine speeds, the compressor and turbine bypass valves on the high-pressure turbo (controlled by the two small actuators) are completely open effectively making the low-pressure turbo do all the work.
The big actuator controls this valve which I think sends all of the exhaust flow to the low-pressure turbo.
The exhaust manifold is integrated in the head. Mazda appears to have done a good job of directing the exhaust flow for optimum performance.
