From: bowers@rigel.dfrf.nasa.gov (Al Bowers)
Newsgroups: rec.autos
Subject: Re: V6 .vs. inline 6
Date: 13 Aug 92 18:57:17 GMT
	<BOWERS.92Aug12121234@rigel.dfrf.nasa.gov>
	<Aug13.083530.19014@engr.washington.edu>
Organization: NASA Dryden, Edwards, Cal.

In article <Aug13.083530.19014@engr.washington.edu> eliot@lanmola.engr.washington.edu (eliot) writes:

>In article <BOWERS.92Aug12121234@rigel.dfrf.nasa.gov> bowers@rigel.dfrf.nasa.gov (Al Bowers) writes:

[nice tutorial on engine balancing deleted]

Thanks.  Actually, that was a simple subset of a piece I wrote for a
magazine that got published about a year ago...

>>Finally, there is firing order balance.  this has _nothing_ to do with
>>mass balance.  All this is, simply, do you get a power stroke with
>>even rotation of the crank?  Ideally, every 180 degrees of crank
>>rotation you want a power stroke in a 4 cylinder, 120 degrees for a 6,
>>90 degrees for a 8, 72 degrees for a 10, 60 degrees for a 12, etc.

>A lot of confusion on various V6s being "unbalanced" comes from the
>above.  A 90 degree V6 will *have* firing order balance if the crank
>has the proper offsets to ensure 120 degrees of rotation per power
>stroke , which in this case would be 30 degrees.  All the respectable
>manufacturers that put out 90 degree V6s do this.  e.g. Honda and
>Audi.  I think 90 degree V6s got their bad reputation from that GM (or
>was it Ford) hack job.  Finally consider the VW narrow angle V6.  If
>crank offsets were not used, imagine the resulting shake and rattle.

Right.  The engine you are thinking of is the Buick V-6 from about
1964.  The engine had shared rod journals originally in a 90 degree
V-6.  As the engine had a substantial flywheel, and was built to
produce lots of torque (revving it hard was not its original mission
in life, so it had ohv and mild cams), at it's very low idle, the
firing order unbalance was _very_ noticable.  GM later corrected the
problem by offsetting the rod journals, thus giving firing order
balance _AND_ mass balance in a 90 degree V-6.  Note that the usual
route a 90 degree V-6 is created from is strictly due to shortening a
design from a V-8 to a V-6 by lopping off two cylinders.

>Al, are there any differences in mass balancing between a 90 degree V6 and
>a 60 degree one?  

Yes.  Without crank offsets you can never get a mass balanced and
firing order balanced V-6.  Two classical examples:

1/ 90 degree V-6 used in the Maserati Merak and Citroen SM
(Sport-Maserati).  this design started life as a 90 degree V-8, but
Citroen needed a V-6, and fast, so the design team at Maserati simply
sawed two cylinders off a V-8 (the prototype was made _exactly_ this
way, conjurs up a funny image of an Italian technician holding a hack
saw over a V-8 and asking "You wanna me to do what?!?").  As the
engine was made from the beginning to be a high revving engine (dohc,
with cam drive off the _middle_ of the cams in the middle of the
engine to reduce cam shaft whip), and had a very light flywheel, it
idled high.  In the car, this is barely even noticable as a lumpy
idle.  In fact, the better the tune on the car, the more evident this
is (lower idle, more lumpiness).  If you _touch_ the engine while it
is running, it is quite apparent the engine is very smooth (mass
balanced).

2/ Alfa Romeo 60 degree V-6 used in the Alfa Romeo GTV6, the Milano/75
and the ES 30/SZ (Sport Zagato).  This engine is not mass balanced
(though it strikes the optimal compromise to be such), but idles
smoothly when seated in the car.  Touch this engine at idle and it
feels like a paint shaker in comparison to the 90 degree V-6.  The
vibration is easily taken out in automotive applications by motor
mounts.  No compromise to the structure is made as the engine is
_surrounded_ by the frame of the car.

Footnote: Motorcycle applications _usually_ require a solidly mounted
engine (the engine is stressed as part of the frame) and so must be
solidly mass balanced (90 degree V-twins are perfect examples, such as
Ducati or Moto Guzzi).  The firing order imbalance is simply evident
as a lumpy idle, and most bike applications are much more interested
in high RPMs, so it is a non-issue...

>Lastly, anyone wants to study an inline 5?  The shakes are longitudinal!!
>Honda places the middle cylinder directly over the drive shafts, while
>Audi cantilevers the entire engine over the driveshafts and uses the mass
>of the gearbox to counter it.  Lots of soft mounts used in both cases.

I never understood the need for a 5.  If a 4 can fit, you can slot in
a V-6 (ala VW) or even maybe a V-8.  %s are just a 4 with an extra
hung on the end.  What an abortion...

--
"Time is simply the illusion of the passing of history, and history is
simply the illusion of the passing of time..."
                                -The Hitch Hiker's Guide to the Galaxy
Iaido   Takamine   Hobie   Rossignol   Alfa GTV6  Ducati MHR(DOD #900)