Quote:
Originally Posted by Coheed
Low end combustion on the FA20 is good. Mid range is where there is an issue.
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The torque dip is not because of combustion efficiency. There is no combustion efficiency issue in the midrange. Combustion efficiency is basically only a problem at low speed.
Currently, low speed combustion is okay because there is the D4-S system, and because the ports are designed to make it work. Low load the direct injectors do their stratified charge thing, high load port injectors supply some fuel because the DI can't mix the fuel well alone. Subaru wants to ditch this setup but keep direct injection, which is why they are bringing TGVs in. Direct injection requires high tumble flow to work, but a high tumble port restricts airflow. The TGV allows good top end power when open, good low end charge motion when closed.
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Dimman, arghx7 said the ports on this are not what you'd call high flow ports. He said D4-S just allows you to strike a better compromise than the usual high tumble port + DI combo. Remember that the direct injectors are providing all the fuel below some load level.