-------
12
3. During actual road trips the fuel economy achieved was within
10% of the EPA Highway Cycle dynamometer fuel economy results for each
car. Every car achieved results equal to or in excess of its "Buyers
Guide" rating.
However, during the course of the test program it was noted that
significant fuel economy penalties occurred when highway speeds went
above the 55 miles per hour speed limit, especially for small cars.
4. Based on previous studies of non-urban driving patterns and the
results of this test program, it is concluded that the procedure used by
EPA for the determination of non-urban fuel economy produces results
that are representative of what drivers can expect during highway
driving, if travel is not constrained by heavy traffic, the 55 mph speed
limit is obeyed, and weather and road conditions are favorable.
Additional Discussion
During the course of the test program some analysis was done to
determine the possible cause of the complaints voiced by some drivers
about the highway fuel economy of some 1975 models. Assuming the
vehicle is in a proper state of tune, it was concluded that four factors
could be having a significant effect:
1. Mileage driven in congested traffic conditions or urban areas
most likely will be included in the driver's calculation since the only
computational method available to the typical driver is to monitor
mileage between refuelings and to record the amount of fuel dispensed
during refueling.
2. The trips taken may be so short that the cold start and warmup
effect is significant.
3. The 55 mph speed limit may have been exceeded often and for
long periods of time.
4. Seasonal and weather factors may have been ignored or at least
not understood.
An example of how the first factor can affect mileage is cited
below:
A driver travels from a point in City A to a point in City B,
a distance of 100 miles, in the Ford Pinto test car used for
this program. Starting with a full tank of gas he leaves his
-------
11
Table 2 shows the agreement between carbon balance fuel economy and
volumetric fuel economy achieved during the dynamometer tests. The
overall average difference between the carbon balance and volumetric
fuel measurement was 1% with the carbon balance yielding the higher
results.
Detailed fuel economy and emissions results appear in the Appendix.
It was not determined until after the test vehicles were returned that
one vehicle failed to meet the applicable CO emission standard by a
substantial margin and another vehicle failed to meet the NOx standard.
The reason for the failures could not be determined but they would not
necessarily have influenced the economy results.
Summary and Conclusions
1. For dynamometer tests on the six production vehicles tested,
the average difference in Highway Cycle fuel economy from the pre-
production cars tested in the EPA certification program was only 1.5%.
The maximum deviation for any one car was 12.9% low for the Volkswagen
Rabbit. All other test cars were within 10% of the certification car
results. This may not be outside the range of difference that could be
expected from vehicle to.vehicle differences.
2. The average fuel economy the test cars achieved when driving
the EPA Highway Cycle on a test track was 5% lower than achieved during
dynamometer tests. No trend with vehicle weight was apparent, as. the
two vehicles with track fuel economy closest to dynamometer fuel
economy were the Volkswagen Rabbit (2250 inertia weight) and the Lincoln
Continental (5500 inertia weight). A 5% agreement between track and
dynamometer results is especially encouraging in view of the limited
number of tests run and the fact that the test track had a rather rough
surface (which would reduce fuel economy) and no attempt was made to
establish specific road load information for all of the test cars. The
standard look-up table horsepower is representative for most vehicles,
but some streamlined or poorly shaped vehicles can have actual road
load horsepower requirements that are sufficiently different from the
standard values to cause a measurable difference in fuel economy.
Provisions in the EPA procedures already allow for determination of
specific road load data for test cars to be used in setting the dyna-
mometer. Programs are currently underway to develop procedures for
determining vehicle-specific road load information for all vehicles
tested.
-------
looV-
FIGURE 11 - EFFECT OF TRIP LENGTH ON COLD-START
CITY FUEL ECONOMY
Pre-Emission
Controlled Vehicles
XD A 1973 Vehicles
ill l L
7 8 9 10
Trip Length - Miles
11
12 13 14 15 16 17 18
50
(0
o
u
v
7)
4)
30
20
10
Volkswagen Rabbit
Lincoln Continental
Chevrolet Chevelle
10 20 30 40 50 60 70
miles/hour ,
80
Figure 12 - Steady State Fuel Economy vs. Speed
-------
13
home in City A and drives 10 miles through the city before
getting on the highway. Entering City B he drives 10 miles
before pulling into a gas station where he fills the tank.
Based on the results published in the Buyer's Guide the driver
expects to get 26 mpg. But his car takes 4.2 gallons to fill
it up indicating only 23.8 miles per gallon, 8.5% less than he
expected. What's wrong?
The driver forgot to consider the 20 miles of urban operation
between fill-ups. Even if the car did get 26 mpg on the
highway the lower fuel economy achieved during the relatively
urban portions of the trip would be enough to pull the average
down to 23.8. The correct formula for mileage estimation for
this case would be:
2
18 26
23-8
where :
o .2 is the fraction of urban operation,
o 18 is the Urban Cycle fuel economy (from the Buyer's Guide),
o .8 is the fraction of highway operation
o 26 is the Highway Cycle fuel economy (from the Buyer's Guide).
An example of how the second factor, short trips, can affect fuel
economy is apparent from inspection of Figure 11. Only on trips beyond
20 miles in length can the effects of warmup be ignored. The EPA Highway
Cycle is a hot start test which means it will accurately predict only
long trips. However, it will still rank cars correctly for shorter
trips.
The effect of excessive speed on highway fuel economy can be estimated
from the steady speed cruising data which was generated during the test
program. As shown in Figure 12 the reduction in fuel economy at speeds
in excess of 55 mph was significant for all six vehicles. The smaller
cars tended to be most affected by higher speeds. For example, the
Volkswagen Rabbit had 30% better fuel economy at 55 mph than at 70 mph
while the Chevrolet Chevelle was 14% better at 55 than at 70.
-------
15
An additional factor which can significantly affect fuel economy is
ambient temperature. The EPA dynamometer tests are run at about 77 F.
A fuel economy loss of about 2% for every 10 F drop in temperature can
be anticipated. For this reason drivers who keep accurate records of
their economy will notice a pronounced drop in mileage during winter
weather unless a change in their driving pattern masks this effect.
Recognizing that the differences between drivers and usage patterns
can result in substantial differences in fuel economy for a given model
of car, it seems desirable for EPA to report more than one fuel economy
rating for each model. The present city and highway cycles allow the
customer to rank cars based on the type of driving which he does most.
If it appears however that the average motorist will expect to achieve
the "highway" rating regardless of the speed at which he drives and
regardless of the amount of urban operation mixed with his highway
driving, then it can be anticipated that some dissatisfaction with the
entire fuel economy program will result. In this situation it would
seem desirable to stress the composite city/highway number in the
Buyer's Guide and in advertising and point out to the customer that
strictly city driving can be expected to produce lower results while
strictly highway driving at legal speed limits should produce better
results.
-------
Appendix 1
Test Vehicle Descriptions
-------
TEST VEHICLE DESCRIPTION
Chassis model year/make - 1975 Chevelle Malibu, 2 door
Emission control system - EGR, quick heat intake manifold, catalyst
Engine
type V8
bore x stroke 4.00 x 3.48 in./102 x 88 mm
displacement 350 CID/5700 cc
compression ratio . 8.20:1
maximum power @ rpm 145 hp/108 kW (§ 3800 rpm
fuel metering 2 barrel
fuel requirement 91 RON
Drive Train
transmission type automatic
final drive ratio 2.73
Chassis
type front engine, rear drive, body frame
tire size G 78-14
curb weight
inertia weight 4500
passenger capacity 4
Emission Control System
basic type EGR/EFE/CAT
mileage accumulated on system . . . 11420
-------
TEST VEHICLE DESCRIPTION
Chassis model year/make - 1975 VW Rabbit, 4 Door
Emission control system - EGR, air injection, catalyst
Engine
4 cyl. OHC
type .
bore x stroke 3.012 x 3.149 in./77 x 80 mm
displacement .I!!!'.'.!!'.'. 90 CID/1500 cc
compression ratio 8.0:1
maximum power g rpm ™ SAE hp/52 kW <§ 5800 rpm
fuel metering 2 Barrel
fuel requirement 91 RON
Drive Train
transmission type 4 speed manual
final drive ratio 390
Chassis
transverse front engine, front drive,
type unitized body
tire size 155 SR-13
curb weight
inertia weight 2250
passenger capacity . . 4
Emission Control System
basic type EM/EGR/AIR/CAT
mileage accumulated on system . . . 6254
-------
TEST VEHICLE DESCRIPTION
Chassis model year/make - 1975 Ford Pinto Runabout
Emission control system - EGR,. .air injection
Engine
type 4 cyl. OHC
bore x stroke . . 3.78 x 3.13 in./96 x 80 mm
displacement 140 CID/2300 cc
compression ratio 8.4:1
maximum power @ rpm 85 hp/63 kW @ 4800 rpm
fuel metering 2 Stage, 2 Barrel
fuel requirement 91 RON
Drive Train
transmission type 4 speed manual
final drive ratio 3-18
Chassis
type front engine, rear drive, unitized body
tire size BR 78-13
curb weight
inertia weight 3000
passenger capacity . . 4
Emission Control System
basic type EGR/AIR
mileage accumulated on system . . 7500
-------
TEST VEHICLE DESCRIPTION
Chassis model year/make -1975 Firebird, 2 Door
Emission control system - EGR ,quick heat intake manifold, catalyst
Engine
type in line 6 cyl.
bore x stroke 3.88 x 3.53 in./99 x 90 mm
displacement 250 CID/4100 cc
compression ratio 8.22:1
maximum power @ rpm 105 hP/78 kw @ 380° rPm
fuel metering * Barrel
fuel requirement 91 RON
Drive Train
transmission type 3 speed manual
final drive ratio 3.08
Chassis
type front engine, rear drive, unitized body
tire size F 78-14
curb weight
inertia weight 4000
passenger capacity . . 4
Emission Control System
basic type EGR/EFE/CAT
mileage accumulated on system . . 3700
-------
TEST VEHICLE DESCRIPTION
Chassis model year/make - 1975 Ford Granada, 2 Door
Emission control system - EGR, air injection.
Engine
type . in line 6 cyl.
bore x stroke 3.68 x 3.91 in./93 x 99 mm
displacement 250 CID/4100 cc
compression ratio 8.0:1
maximum power @ rpm 86 hp/64 kW @ 3000 rpm
fuel metering ..... 1 Barrel
fuel requirement .91 RON
Drive Train
transmission type automatic
final drive ratio 3.00
Chassis
type front engine, rear drive, unitized body
tire size DR 78-14
curb weight
inertia weight 3500
passenger capacity . . 4
Emission Control System
basic type EGR/AIR
mileage accumulated on system . . . 12675
-------
TEST VEHICLE DESCRIPTION
Chassis model year/make - 1975 Lincoln Continental, 4 Door
Emission control system - EGR, air injection, catalyst
Engine
type V8.
bore x stroke 4.36 x 3.85 in./Ill x 98 mm
displacement 460 CID/7500 cc
compression ratio 8.0:1
maximum power @ rpm 253 hp/188 kW @ 4400 rpm
fuel metering .... 4 barrel
fuel requirement 91 RON
Drive Train
transmission type automatic
final drive ratio 2.75
Chassis
type front engine, rear drive, body frame
tire size 230 x 15 R
curb weight
inertia weight 550°
passenger capacity . . .6
Emission Control System
basic type EGR/AIR/CAT
mileage accumulated on system . . . 8375
-------
Appendix 2 - Fuel Economy Results (MFC)
.
: Ford Granada
: 250 CID, no cat,
A-3
• i •
Guide: 14 city/18 highway
i
! Pontlac Firebird
1 250 CID, M-3
i
• Guide: 16 city/21 highway
j Chevrolet Chevelle
! 350 CID, A-3
j
i
• i
! Guide: 13 city/18 highway
i Ford Pinto
I 140 CID, no cat,
! M-4
l
i
' Guide: 18 city/26 highway
j Lincoln Continenal
i 460 CID, A-3
1
j
< Guide: 10/15
VW Rabbit
i 90 CID, M-4
'; Guide: 24 city/38 highway
Mfr Cert
EPA Cert
Dyno C.B.
Dyno Vol.
Track
Road
Mfr Cert
EPA Cert
Dyno C.B.
Dyno Vol
Track
Road '
Mfr Cert
EPA Cert
Dyno C.B.
Dyno Vol
Track
Road
Mrf Cert
EPA Cert
Dyno C.B.
Dyno Vol
Track
Kond
Mrf Cert
EPA Cert
Dyno C.B.
Dyno Vol
Track
Road
Mfr Cert
EPA Cert
Dyno C.B.
Dvno "ol
Track
Road
•75 FTP
14.0
14.5
13.0
13.1
14.6
15.3
17.0
17.3
None
13.3
14.0
13.4
17.5
17.7
17.8
17.6
9.3
9.6
9.3
9.8
23.4
24.8
24.4
?3.«
Hot
•72 FTP
14.0
14.1
12.5
17.4
17.8
16.4
14.6
13.7
13.1
18.9
18.6
16.6
10.2
10.5
10.3
26.1
25.n
24.0
11WC
18.5
17.8
18.2
18.9
16.5
22.1
23.2
24.4
25.3
23.8
None
17.5
19.4
18.7
17.7
28.2
28.4
28.1
27.6
25.5
14.1
15.1
15.0
15.5
16.2
35.8
39.6
36.9
34 . 5
33.7
Road Trip
mpg @
Avg. Speed
18.6 @ 50.2
25.0 @ 51.9
19.2 @ 50.4
26.9 @ 48.3
16.2 @ 49.9
37.7 @ 49.2
Gal/Hr.
0 mph
.628
.586
.706
.664
.698
.690
.426
.485
1.008
1.018
.383
.353
15 mph
13.8
14.3
19.5
20.1
19.0
18.1
18.4 2nd
18.9
14.2
14.3
14.2
31.1
31.6
31.1
30 mph
19.5
20.2
17.9
19.9
31.4
32.0
29.4
20.5
20.0
17.6
37.5 4th
33.2
31.1 4tl
17.6
17.6
17.6
18.0
49.8 4tli
49.7
45.5 4tll
45 mph
19.1
20.8
19.4
19.6
27.7
28.4
27.8
20.5
20.1
18.9
31.8
30.8
28.2
17.3
17.3
18.1
18.1
41.8
41.6
38.4 .
60 mph
17.4
19.5
16.6
17.3
*
22.3
23.6
23.8
18.2
18.0
17.4
28.9
26.7
24.2
15.5
15.8
16.4
16.4
32.2
31.2
29.2
70 mph
14.5
20.7
16.1
20.8
14.9
24.8
8(Lmph
10.2
17.9
13.9
17.5
13.2
21.6
Test ,u
Weight*
3500
3500
3500
3500
3800
3700
4000
4000
4000
4000
4030
4060
4500
4500
4500
4500
4380
4300
3000
3000
3000
3000
3040
3040
5500
5500
5500
5500
5610
5610
2250
2250
2250
2250
2430
2430
Legend? Mfr Cert = certification car results based on manufacturer's .test (carbon balance)
EPA Cert = certification car results based on EPA test (carbon balance)
Dyno C.B. = dynamometer carbon balance test results of production car used in test program
Dyno Vol - dynamometer volumetric fuel meter results of production car used in test program
Track •» track test, results (volumetric fuel meter)
Aol- T*o<3ii1t-a (\It\ 1 l
fllf»l
^Dynamometer Test weight duplicated
the value used during certification
testing but track and road test
weight depended on the particular
drivers and equipment used.
-------
Table A-l
Vehicle Emissions
Ford Granada
Fuel Economy MPG
Carbon
Test No.
16-1269
16-1271
16-1269
16-1270
16-1272*
16-1370
16-1369
16-1273
16-1371
Test
75 FTP
Hot 72 FTP
Hwy
Hwy
Idle
15
30
45
60
Gear
D
D
D
D
P
D
D
D
D
HC gm/mi
.76
.60
.34
.37
.15
.43
.18
.18
.21
CO gm/mi '
11.7
5.8
3.0
2.6
.44
2.3
2.0
2.1
2.3
C02 gm/mi
664
622
483
483
92
640
451
460
507
NOx gm/mi
3.40
3.25
4.44
3.38
.06
1.03
1.33
2.04
4.43
Balance
13.0
14.0
18.1
18.2
.628
13.8
19.5
19.1
17.4
Volumetric
13.1
14.1
18.5
18.9
.586
14.3
20.2
20.8
19.5
* Idle Gm/Min, Gal/Hr
-------
Table A-2
Vehicle Emissions
Pontiac Firebird
Fuel Economy MPG
Carbon
Test No.
16-1274
16-1275
16-1274
16-1276
16-1277*
16-1372
16-1373
16-1278
16-1374
Test
75 FTP
Hot 72 FTP
Hwy
Hwy
Idle
15
30
45
60
Gear
all
all
all
all
N
2
3
3
3
HC gm/mi
.55
.21
.04
.03
.02
.11
.06
.03
.03
CO gm/mi
8.1
4.1
.4
.13
.01
.12
.07
.03
.03
CO? gm/mi
509
504
364
363
104
453
282
320
398
NOx gm/mi
2.01
2.12
2.54
2.50
.03
.22
.36
1.11
3.74
Balance
17.0
17.4
24.3
24.4
.706
19.5
31.4
27.7
22.3
Volumetric
17.3
17.8
25.2
25.3
.664
20.1
32.0
28.4
23.6
* Idle Gms/Min, Gal/Hr
-------
Table A-3
Vehicle Emissions
Chevrolet Chevelle
Fuel Economy MPG
Carbon
Test No.
15-1384
16-1383
16-1384
16-1385
16-1386
16-1387
16-1388
16-1389
16-1390
Test
75 FTP
Hot 72 FTP
Hwy
Hwy
Idle
15
30
45
60
Gear
D
D
D
D
P
D
D
D
D
HC gm/mi
.33
.20
.05
.05
.02
.09
.08
.06
.03
CO gm/mi
5.6
3.4
.5
.5
.0
.0
.0
.0
.0
C02 gm/mi
626
601
445
465
103
465
433
432
487
NOx gm/mi
2.00
1.71
2.24
2.36
.04
.43
.30
1.11
3.34
Balance
14.0
14.6
19.9
19.0
.698
19.0
20.5
20.5
18.2
Volumetric
13.4
13.7
18.8
18.7
.690
18.1
20.0
20.1
18.0
* Idle Gms/Min, Gal/Hr
-------
Table A-4
Vehicle Emissions
Ford Pinto
Fuel Economy MPG
Carbon
Test No.
16-1342
16-1343
16-1344
16-1345
16-1346*
16-1347
16-1348
15-1668
16-1349
16-1350
Test
75 FTP
Hot 72 FTP
Hwy
Hwy
Idle
15
30
30
45
60
Gear
all
all
all
all
N
2
3
4
4
4
HC gm/mi
.96
.51
.28
.26
.06
.20
.22
.19
.26
.24
CO gm/mi
15.6
10.9
2.4
2.3
3.4
7.6
3.4
5.4
1.6
1.7
C02 gm/mi
470
451
318
304
57
468
308
227
276
304
NOx gm/mi
2.04
2.01
2.40
2.23
.02
.44
.99
.60
1.04
3.46
Balance
17.8
18.9
27.5
28.7
.426
18.4
28.3
37.5
31.8
28.9
Volumetric
17.6
18.6
27.1
28.1
.486
18.9
27.9
33.2
30.8
26.7
* Idle Gms/Min, Gal/Hr
-------
Table A-5
Vehicle Emissions
Lincoln Continental
Fuel Economy MPG
Carbon
Test No.
15-1351
15-1352
16-1353
16-1354
16-1355*
16-1356
16-1357
16-1358
16-1359
Test
FTP
72 Hot FTP
Hwy
Hwy
Idle
15 MPH
30 MPH
45 MPG
60 MPH
Gear
D
D
D
D
P
D
D
, D
D
HC gm/mi
1.65
1.01
0.34
0.38
0.20
0.96
0.35
0.30
0.20
CO gm/mi
52.7
32.7
6.0
5.6
7.9
35.4
8.73
3.71
4.24
CO? gm/mi
864
818
580
579
136
568
489
507
565
NOx gm/mi
1.90
1.80
2.98
3.04
0.04
0.24
0.85
1.45
3.70
Balance
9.3
10.2
15.0
15.1
1.008
14.2
17.6
17.3
15.5
Volumetric
9.8
10.5
15.5
15.4
1.018
14.3
17.6
17.3
15.8
* Idle Gms/Min, Gal/Hr
-------
Table A-6
Vehicle Emissions
VW Rabbit
Fuel Economy MPG
Carbon
Test No.
15-1607
15-1608
15-1607
15-1608
16-1609*
16-1610
16-1611
16-1612
16-1613
16-1614
Test
FTP
72 Hot FTP
Hwy
Hwy
Idle
15 MPH
30 MPH
30 MPH
45 MPH
60 MPH
Gear
All
All
All
All
N
2nd
3rd
4th
4th
4th
HC gm/mi
0.68
0.22
0.07
0.60
0.01
0.21
0.08
0.11
0.07
0.02
CO gm/mi
5.6
1.8
0.5
0.1
0.0
0.0
0.1
0.0
0.1
0.1
CO? gm/mi
353
337
245
234
57
285
241
178
212
275
NOx gm/mi
0.68
0.71
0.77
0.68
0.03
0.36
0.41
0.62
0.65
0.57
Balance
24.4
26.1
36.1
37.1
0.383
31.1
36.8
49.8
41.8
32.2
Volumetric
23.8
25.0
34.8
34.1
0.353
31.6
37.0
49.7
41.6
31.2
* Idle Gms/Min, Gal/Hr
-------