Quote:
Originally Posted by Hersbird
Modern direct injection can eliminate the throttle then add cylinder deactivation and variable cam profiles to that. A non-hybrid can also be optimized to have just enough power for cruising speed and the ability to add more power when needed.
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I don't think you understand what direct injection does. It does not eliminate the throttle.
The most sophisticated variable cam profile systems allow throttle plate elimination at the cost of greater valvetrain power consumption. Honda's R18 and 3-stage VTEC motors allow a rough approximation of this capability, allowing a greater proportion of high throttle position operation.
Even without the throttle restriction, thermal efficiency is still horrible at low load because the combustion temperature and pressures are so low and mechanical efficiency is also low. There is no getting around a combination of downsizing + power adders, shutting the engine off, and using longer gearing.