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Electric engine vs ICE engine consumption

Discussion in 'Technical' started by Cobos, May 8, 2008.

  1. Cobos

    Cobos S60 Owner since 2013 - sold, S85D owner since 2017

    Jun 22, 2007
    Oslo, Norway
    I thought I'd throw out another question for you technically knowledgable persons.
    I seem to have caught somewhere that an electric engine doesn't get much less efficient at smaller loads as the power increases? In other words if I have a 30kW electric engine and a 225kw engine and my 2500lbs car is moving on a flat normal road at 40mph, assuming everything else is equal how much power would each engine draw?

    The reason I ask is that my impression is that using ICE engines without any special fuelsaving measures like cylinder deactivation the difference would be huge. Lets say between a 75kW I4 and a 150kW I4 using the same speed and road above the bigger one would be using around 80% more fuel than the smaller one?

    Anyone that know this?

  2. TEG

    TEG TMC Moderator

    Aug 20, 2006
    #2 TEG, May 8, 2008
    Last edited: May 8, 2008
    From what I can tell, electric motors tend to have high efficiency ( > 90% ) for a wide range of loads anywhere in the 20-100% load range. (I suppose you could hurt real world efficiency by sizing the electric motor WAY too big).

    Gasoline engine efficiency seems rather complicated, and varies a lot based on factors such as RPMs, compression ratio, temperature, intake manifold shape, valve timing, cycle type, etc.

    This air compressor (gas vs electric) chart gives a rough idea of the general differences, but also has air pump losses factored in so the low load efficiency if dragged down for both gas and electric:

    Another thing to consider is that many gasoline cars are saddled with an automatic transmission that wastes more energy in the torque converter.

  3. BBHighway

    BBHighway Member

    Feb 2, 2008
    One place where electric motors really shine is in rush hour traffic. Idling, creeping forward, idling some more, barely ever getting out of first gear; that's what driving around Washington DC, and most other metropolitan areas of the US is like. It used to be just at peak rush hour times, but now in some places it's spread to most of the day. Even Saturday afternoon in places like Leesburg Virginia is a horrible driving experience.

    ICEs are very inefficient in that sort of driving. Electrics don't need to idle, and are still fairly efficient even when operating at low speed, compared to ICEs. The regen braking also works well in that situation. That's why the Prius works so well in city driving.

    There is a really good scientific study called "Well-to-Wheels Analysis of Advanced Fuel/Vehicle Systems — A North American Study of Energy Use, Greenhouse Gas Emissions, and Criteria Pollutant Emissions" from General Motors Corporation, Argonne National Laboratory, and Air Improvement Resource, Inc..

    You can download it from the interweb at :

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