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PONTIAC FIERO
Technical Analysis
 
Pontiac engineers must have had a lot of fun with this project, which 
appears to have been put together in the same spirit as other American 
2-seaters such as the original Corvette and the original T-bird. It's as 
though a bunch of engineer/enthusiasts got together and said, "Okay, let's 
see what existing parts we've got in the bin, and how we can rearrange them 
into a real sports car." This is the same procedure used for building such 
historical favorites as MG's, Triumphs, and others. They take an existing 
driveline/suspension (the hard parts) and incorporate them in a more 
interesting package.
 
In an engineering analysis I find myself comparing the Fiero to the new 
Corvette - not because of any similarity in size of market, but because that 
is America's only other sports car and they share corporate heritage. In a 
full road test, of course, comparative cars might be the Mazda RX-7, Porsche 
944, Datson 280ZX or even the Bertone X1/9.
 
A consideration of the packaging of the Fiero raises the immediate question: 
"Why mid-engine, after Chevrolet just convinced us that front engine was 
proper for the Corvette?" Because the two are aimed at different markets. 
The Fiero was justified in the corporation largely as a mass production 
economy commuter / sports car. This meant that an existing unitary driveline 
package was required. Then, for an aerodynamic hood line, the low seating 
position, short wheelbase and light chassis, the mid engine location was 
justified. The fact that this creates a potentially better handling 
competition car may or may not have been incidental.
 
The Fiero is very wide and short. It has almost a 2in greater track than 
other sports cars in its class, and is about 10 inches shorter in overall 
length. The existing X-car driveline dictates the width (this gives us 
another generation of "wide-track" Pontiacs). But this makes roll and 
handling development easier. Given a 2-seater limitation, the width also 
allows room for a fuel tank beneath the console, right at the center of 
gravity. The mid-engine design gives a moderate 56-percent rear weight, 
partly because of a relatively short rear overhang. When the V-6 becomes 
available, however, approximately 150 extra pounds at the tail will increase 
the rear bias.
 
The 600-lb stamped-steel and spot-welded space frame is being highly touted, 
although it is only a slight deviation from conventional unit construction. 
The primary difference is that none of the steel panels makes up the 
exterior body shell. That is comprised of easily fitted plastic outer 
panels, as described in the main story. The concept is very similar to the 
Corvette except for the precision-fit, mill-and-drill process. The 
percentage of plastic in the body structure is likewise similar to Corvettes 
with about 175 lb of sheet molded compound and reinforced reaction injection 
molded (fiberglass) exterior panels.
 
You can't get Detroit engineers to talk about chassis bearing or torsional 
rigidity these days. Instead they like to refer to vibration frequencies, 
which are problems perceived by commuting minded tourists. Still, for 
enthusiast drivers this chassis is stiff enough. The fixed steel top (no 
T-top is planned) provides an efficient stiffness-per-pound structure that 
can't be approached by any convertible sports car made. Finite element 
analysis of high strength steels were used extensively to produce just about 
the minimum acceptable mass---from a ride comfort standpoint. So it doesn't 
look like there will be any major weight reductions from the base 2500 lb in 
the future unless some costly exotic materials are used. As for impact 
safety, we don't have to worry about whether the engine is up front or is 
back, because Big Brother's standards apply equally to all designs.
 
Aerodynamics may not have been a high priority consideration in the original 
Fiero design. With a relatively low weight and small frontal area (by 
American standards), good EPA mileage figures were possible without going 
for the ultimate in low drag coefficient. The reported Cx is 0.377, which is 
not bad for such a short car, but not too strong an advertising point 
either. The obvious problem is the notchback rear window, which is almost a 
necessary evil in a mid-engine car. Although it allows easy engine access 
and ventilation, it really disturbs the upper air flow and increases drag 
while reducing potential down force from any rear spoiler. The Fiero's other 
problem is the nose-up leading edge of the front bumper. This design allows 
a good open angle and radiator inlet, but it also rams a lot of air down 
under the nose. Not only does this usually increase drag, but it also 
generates a lot of lift, in spite of the bottom-breather radiator inlet. 
Reported front lift figures were about 120 lb at 100 mph, which can be 
significant when the static front weight is just over 1100 lb. It also 
appears that the opened headlight buckets were not as well researched in the 
wind tunnel as the Corvette's, as they raise the Cx to 0.417. Be that as it 
may, the pop-off plastic body panel concept means that better aerodynamics 
can be incorporated easily in the future.
 
The engine/driveline package doesn't provide much of a story this year. 
Basically it is GM's transverse 2.5-liter 4-cylinder sitting on a subframe 
just as it does in the X-car. The cast iron overhead valve engine still puts 
out an everyday 92 bhp, even with an interesting new iron head casting. A 
swirl-port intake that brings the fuel-air charge into the cylinder along a 
spiral path makes its debut in the Fiero. New combustion chamber and piston 
dome shapes keep the charge swirling (and mixing) until ignition. This has 
allowed the compression ratio to be increased from 8.2 to 9.0:1, which is 
surprisingly good these days for an engine without a knock sensor.
 
Otherwise there are very few modifications to the driver line and subframe 
assembly. The transverse transmission is available as either a 3-speed 
automatic with lockup converter and 3.18 final drive, or a 4-speed manual 
with top gear ratio options. Only the "performance" ratio with a 4.10 final 
driver is of interest to the enthusiast, as the 3.32 gear coupled with a 
0.73 4th gear is suitable only for economy runs. The X-car axles are used 
as-is, including the constant-velocity outer U-joints.
 
The engine subframe, however, is not a straight interchange with the X-car. 
At the rear, the rails had to be kicked up to provide a better rear ramp 
angle. (In the front-drive X-car these rails connect to the floor pan at the 
firewall.) And the front rails have had the mount bushings rotated from a 
horizontal plane to a vertical plane. This allows the subframe to pivot 
downward about the front mount bolts for easier engine removal. To absorb 
engine torque reactions, an upper strut connects the cylinder head with a 
sheet metal bracket on the right shock tower. All of these subframe and 
strut mounts are well insulated with rubber bushings, which are great for 
isolating road and engine vibrations from the passengers, but don't do a lot 
for handling.
 
The front suspension is taken almost in toto from the Pontiac T-1000. 
Although not originally designed for a sports car the particular short- and 
long-arm configuration is not to bad in this application. The major 
modifications were to widen the interconnecting subframe to give a 2-in 
wider track and to relocate the shock absorber mounts. On the T-car the 
shock mounts to the upper arm and stands very high in the wheel well. 
Therefore to lower the Fiero's hoodline, the shock now mounts to an 
otherwise standard lower arm. Basically this is a good design, especially 
with the contemporary practice of leading steer arms but somewhere in the 
translation a little too much bump steer seems to have been allowed, causing 
more steering wheel feed back than we are used to.
 
Part of the feedback can be attributed to non-assisted steering --- which I 
prefer. Early in the design it was decided that the low front weight made 
assisted steering unnecessary in most circumstances. The worst situation is 
parallel parking with the optional wide tires. In this case the effort is 
noticeable thought not unreasonable.
 
At the rear, the suspension is essentially indistinguishable from the 
X-car's front layout. Even the trailing steer arms are there, although in 
the Fiero they are anchored to the subframe via tie rods that can still be 
adjusted for toe-in. The combination should give excellent cornering 
compliance understeer qualities. Only a couple of really finicky evaluators 
have perceived slight yaw overshoot, which could be because of lateral 
?bounce? compliance in the engine/suspension subframe. Otherwise the 
handling properties are excellent, with an easily corrected drop-throttle 
oversteer when cornering at the limit. The average roll angle of 3.5 degrees 
per G is reasonable, considering the front anti-roll bar is only 23.0 mm and 
there is none at the rear. The wide track helps, naturally, but not the 
reported 19.5-in center of gravity, which seem high for a car this size.
 
A new disc brake system also appears for the first time on the car with 
Pontiac's adapting two existing front suspension systems to the front and 
rear of this car results in 4-wheel discs, but not steel calipers. Because 
the rear requires a mechanical emergency brake, a standard front caliper 
could not be used. These new single-piston aluminum calipers are essentially 
identical front and rear, except for the rear emergency brake balance. A 
conventual proportioning valve limits rear wheel lockup, although the Fiero 
may have almost the ultimate configuration for ideal braking. Given the 
static rear weight bias, and the reported wheelbase ratio, the forward 
weight shift in breaking will give excellent dynamic balance. Other braking 
advantages in the layout are the central fuel tank, central seating and 
minimal luggage capacity. This means that no matter how the car is loaded, 
the optimum brake balance will hardly vary.
 
A lightweight car without a power assisted steering option, you might ask 
why power assisted brakes are standard. The first information given was a 
lack of space in the pedal area for the mechanical leverage. A second reason 
was an unexpected "knock-back" problem with the 4-wheel discs, which use so 
much pedal travel. One hopes this will be sorted out eventually, allowing a 
non-boosted system and the resultant better response.
 
The standard wheels and tires are fairly conventional P185/80R-13 steel 
radials on 5 1/2in wide steel rims. These provide low rolling drag for fuel 
economy and contribute to the low base price. However, those hoping to 
upgrade the appearance of the Fiero will opt for the same-size turbo-finned 
aluminum rims. And true enthusiasts will demand the "high-tech" 14 x 6in 
aluminum wheels with P215/60R-14 Eagle GTs. There appears to be plenty of 
room for expansion in the wheel wells. Pontiac engineers present at the 
introduction confessed that they hope to have a 50-section tire option 
available next year. Of course, even if the extra-wide wheels didn't fit, it 
wouldn't be difficult to add optional flared fender panels.
 
The optional Eagle GTs are the main ingredient in the WS6 special 
performance package, which also includes stiffer front springs, stiffer 
front and rear shocks, stiffer rubber mounts and bushings but no change in 
the standard front anti-roll bar. For quicker steering response, the 
steering rack is mounted more rigidly, and a rubber link in the steering 
shaft is stiffer.
 
The stated goal in the performance package was to make the Fiero equivalent 
in every respect to the Firebird WS6 option, but it was fairly obvious that 
they hadn't met that objective. The transient response is excellent, though 
not exactly what you might like in a true sports car. The problem in 
transferring handling technology from the Firebird is the basic difference 
in weight distribution and wheelbase. With springs bushings selected to 
avoid vibrations and freeway pitch oscillation, this doesn't allow much 
flexibility for response tuning---so far.
 
Technically speaking, what Pontiac has for the enthusiast is a diamond in 
the rough with microscopic flaws. Remember, the stated justification for the 
Fiero was that it be a relatively high volume, economical commuter car. At 
that, they have succeeded admirably. Now they can spend a couple of years 
tuning it with option packages to satisfy the closet racer. The potential is 
exciting. They have all the pieces in the right places, so now someone just 
has to come along with slightly better pieces. If there are a lot of people 
out there who regret not having bought (and kept) one of the first 1953 
Corvettes, this is a second chance. ---Paul Van Valkenburgh 
 

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