Quote:
Originally Posted by amcmike
Actually it is, and today's OEMs do.
Modern engines use much higher compression ratios, enabled by direct injection. The higher SCR increases efficiency even at part throttle, thus increasing fuel economy (in addition to increasing torque under wide open throttle). They can get away with these compression ratios due to the charge cooling as the fuel is injected directly into the combustion chamber (especially with multiple injection strategy at under medium loads and low-mid rpm). This then allows them to downsize the engine displacement (if desired) to further improve fuel economy. This is why OEMs use DI even on small economy cars, not just performance vehicles.
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I should have said,
one of the reasons. The other of course, being emissions (with the exception of particulate emissions, which is actually higher than port fuel).