Engine swapping and design considerations.

[Gross Scruggs <GScruggs@wposmtp.nps.navy.mil>]

Just can't let this engine swapping thread pass without a comment.  There seems
to be a view that suggests a sancitity about the hardware that comes from a
factory.  That if it was designed that way it is because some clarity of insight
led to that solution and one has no right to tamper with it.  Let's look for a
moment at the designer's world.

Draw an equilateral triangle.  Label one point, "performance;" the second,
"versatility;" and the third, "cost."  Put a dot in the center.  The center dot
is perfection, the ideal, the goal. The area of this triangle is constant.  As
any one parameter gets close to the goal, the center, the other two must move
farther away to preserve the constant area.  

For example:  Your assignment is to build a truly high performance car.  No
sweat... you pencil in carbon fiber for strength and reduced weight, forged
aluminum suspension components, a multi-valve, many-cylinder engine with several
turbos, a state-of-the-art computer controlled ignition and fuel distribution
system that also monitors traction availability.  Yes, your goal is attained...
you've made a competitor to the McLaren F1/ Lamborgini Diablo VT/ Porsche GT1. 
But notice what happens to the design triangle.  Your performance point is
getting pretty close to the center... the ideal, but the other two are getting
rather far away from the center, the area must be constant!  This means the cost
is going to be very high, and the car is not going to be very versitile.  You
can't haul sheets of plywood up to the cabin with this baby, and this is not the
transport for the kid's soccer team, and oh yes... it costs a million dollars
and your insurance man just fainted.

Your next assignment is to make everyman's car, the common denominator,
transportation for the masses for the minimum cost.  Minimum cost, purchase and
operation, is the holy grail for this project.  Make the body and frame from the
very cheapest grade of outdoor plywood you can find.  Power by Briggs and
Stratton engines made in China... you get the picture.  You have reached the
goal of minimun cost... getting to the center of your triangle, and notice that
the performance point is getting farther and farther away... as is vertatility,
this thing will not capable of much at all.  Congrats, you have just made a
Trabant.

You see how the design triangle works.  No real design project is that clear cut
or that easy.  Were you to design a vehicle for maximum versatility would it be
more like a Kia Sportage, a Range Rover, or a Lamborgini LM-002.  The
compromises are constant, inescapable, and agonizing.  

Consider the WWII Corsair... Pappy Boyington's bent wing fighter?  The wing was
not bent for aesthetic considerations.  The wing configuration is the result of
a compromise between the structural team, the weight and balance team, and the
engine team.  To achieve the required performance the engine team needed a prop
with a large diameter to put the hp into the air, which required a long landing
gear for ground clearance, the landing gear had to be very robust to withstand
carrier landings and was thus very large and heavy.  The weight and balance team
said to the engine team that more power would be needed to compensate for the
extra weight, necessitating a larger prop...   And a compromise was reached to
bend the wing downward to shorten the length of the gear and still retain ground
clearance for the prop.  

In the case of Audi and adoption of the 5-cyl engine... I can only speculate at
the reasons but the process I will guarantee.  This is my script.  When the
corporate decision was made to develop a successor to the first generation 5000
the target audience (no pun) was isolated, a cost point was established, marque
image and corporate coals were factored in, and the Type 44 was established. 
Certainly the drivetrain engineers were itching to start with a clean sheet of
paper and do an engine to thrash the BMW five-series on road and track.... but
wait, says the accounting team, if you add the engine development costs to the
unit selling price of each vehicle you'll exceed your cost point... sell fewer
units and we'll loose money... so use the existing engine and do whatever you
must to keep performance in line with image requirements... but no new engine. 
On and on, and we now own decendants of that process.

The design process pushes the performance point of the triangle as close to the
center as possible for the compromises that are allowable at the cost and
versatility points.... and that is the art of design.

There is nothing sacred about the 5-cyl Audi engine, it was (likely) used for a
non-performance reason and we are free to replace, or not, it for a performance
reason.  Looking at a bare 5-cyl head it is easy to see that the design itself
is an add-on to an existing 4-cyl engine.  Clever, certainly, and not the first
time this has been done... ultimate?  Not even close.  Like is said of the
Porsche 911, one of my favorite cars, "... you can't make a race car from a
pig... but you can make a very fast pig!"

Genius in the Type 44 is the drivetrain.  The suspension needs a bit of work,
the brakes need help to use the car as we want, more power is definitely
needed... but you don't see anyone ditching the quattro characteristic.  Start
from there... replace stuff as required... repeat until smiles outnumber frowns.

My choice for an ideal engine in my '87 5kCSq... the three rotor Mazda 20B
engine.  Light, smooth, very powerful, about a dozen moving parts... and I'm not
likely going to do it as the process would extend the cost point on my design
triangle to exceed my resources.   

Now if you'll excuse me... I must go buy some lottery tickets.

Regards,  Gross Scruggs
Comments welcome, clarifications appreciated, corrections tolerated, diatribes
ignored.