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I-4 Vs I-6

  1. Aug 1, 2014 #1
    I've noticed that engines have gotten very complicated, thus more complicated in the past few years in to squeeze more power and efficiency out of them, Ford's ecoboost in particular. I was wondering if it would be just as efficient to equip FWD cars with a small, very undersquare inline sixes instead of inline four engines of equal lengh? For example, could you build an inline 6 with a bore of 2" and a stroke of 4" instead of a 4 banger with a bore of 3-3.5" and a stroke of 4"? Would the extra low-end torque give the engine better efficiency or would any gains be canceled out by the extra "surface area" (cylinder side-wall area?). Would such an engine have such poor aspiration that it would need a turbo to be compareable in power in to an inline 4 of similar displacement?
  2. jcsd
  3. Aug 3, 2014 #2
    - with more cylinders you have more friction losses. no way around it.
    - if I remember old japanese/bmw low volume 6 cyl. engines (2.0-2.5) had bit lower specific torque, but higher specific power output... fuel consumption was always worse than any 4cyl. if I
    - from lots and lots of engine specs (mfr specs form car magazines) I have seen, stroke has no (or not significant) effect on maximum torque. all modern petrol engines produces 90-110Nm/l. no matter if oversquare or undersquare.
    - more thermal losses from smaller cylinders. no way around that.

    so I would say (but correct me if I'm wrong) that no problem with matching power or torque output to 4cyl, but worse fuel consumption / efficiency.
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