Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Comparison of two engines of the same displacement

  1. Dec 14, 2012 #1
    Hi all,

    I have this question, and hope you could help me to solve.

    There are two engines with the same displacement (say 250cc). One with smaller piston and the other bigger. Of course the first one will move longer.
    If everything else is the same or similar, generally, which engine is the stronger ?

    Thanks for any input.
  2. jcsd
  3. Dec 14, 2012 #2
    With a larger piston you can have crank/ rod geometry which favors higher rpm (because the piston acceleration is lower). Which means you can get more power.

    I believe the longer stroke of the smaller piston favors higher low-end torque, which makes this the "stronger" engine (stronger, but less powerful).

    I'm sure there is more to it than that, so someone else please chime in...
  4. Dec 14, 2012 #3
    With a short stroke a problem arises with clearance for the valves makers of high performance engines tend to favour an equal bore and stroke a so called square design
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook