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From: eliot@lanmola.engr.washington.edu (eliot)
Newsgroups: rec.autos
Subject: horizontally opposed/boxer engines (was: V4 V6 V8 V12 Vx?
Date: 24 Apr 1993 18:01:03 GMT
Organization: skulls 'r us
Lines: 42
Message-ID: <Apr24.173611.21612@engr.washington.edu>
References: <1r6kcqINNhmp@sumax.seattleu.edu> <Apr22.202724.24131@engr.washingt <1993Apr24.125621.7311@magnus.acs.ohio-state.edu>
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In article <1993Apr24.125621.7311@magnus.acs.ohio-state.edu> bqueiser@magnus.acs.ohio-state.edu (Brian J Queiser) writes:
>There are two crank configurations for
>the flat 4; the most common one is probably the crank that is very
>similar to the I4 crank.

which flat 4 engines have I4 style cranks?

>  Comparing those two engines, the I4 and the
>flat 4 have no first order shaking forces or rocking moments.  The
>I4 has a second order shaking force, while the flat 4 has a second
>order rocking moment.  The significant thing about the flat 4's
>second order moment is that it can be easily balanced out by adding
>mass at the ends of the crank.  The I4, however, requires a counter
>rotating shaft with mass to balance out the second order forces.

i am 99.99% sure that subaru (and porsche) use the boxer configuration
and not the inline 4 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 4 is easier to fit under low hoods
>and in rear compartments (for mid or rear mounting).  The I4 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 4, so even if it is mounted
longitudinally it will not take up lots of length.. and a longitudinal
placement is easier for a 4 wheel drive drivetrain.

i think that subaru's ads hold water.  in practice, their flat fours
are noticeably smoother than inline 4s 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
