horizontally opposed boxer engines was v v v v vx in article apr magnus acs ohio state edu bqueiser magnus acs ohio state edu brian j queiser writes there are two crank configurations for the flat the most common one is probably the crank that is very similar to the i crank which flat engines have i style cranks comparing those two engines the i and the flat have no first order shaking forces or rocking moments the i has a second order shaking force while the flat has a second order rocking moment the significant thing about the flat s second order moment is that it can be easily balanced out by adding mass at the ends of the crank the i however requires a counter rotating shaft with mass to balance out the second order forces i am sure that subaru and porsche use the boxer configuration and not the inline crank that you analyzed and compared would you care to re evaluate the other case of a flat four i think that this configuration is perfectly balanced as far as primary secondary forces and couples are concerned i have an article in front of me that says so bottom line the biggest difference between the engines would probably be their intended use the flat is easier to fit under low hoods and in rear compartments for mid or rear mounting the i can be mounted transversely to reduce hood length read cab forward other than that there isn t much fanfare to the differences between them no matter what subaru ads say technology shared with porsche indeed the flat four is also shorter than an inline so even if it is mounted longitudinally it will not take up lots of length and a longitudinal placement is easier for a wheel drive drivetrain i think that subaru s ads hold water in practice their flat fours are noticeably smoother than inline s and completely buzz free though some may not like its peculiar note but as alfa has shown a boxer four can produce a spine tingling scream that only the likes of recent hondas can approach eliot
