FUEL ECONOMY 

AND 

EMISSION CONTROL 

UNITED STATES 

ENVIRONMENTAL PROTECTION AGENCY 

OFFICE OF AIR AND WATER PROGRAMS 

MOBILE SOURCE POLLUTION CONTROL PROGRAM 

November 1972 
FUEL ECONOMY 

AND 

EMISSION CONTROL 

UNITED STATES 

ENVIRONMENTAL PROTECTION AGENCY 

OFFICE OF AIR AND WATER PROGRAMS 

MOBILE SOURCE POLLUTION CONTROL PROGRAM 

November 1972 
OUTLINE 

I. INTRODUCTION 

II. DEFINITION 

III. FACTORS AFFECTING FUEL ECONOMY 

IV. EMISSION CONTROL EFFECTS ON FUEL ECONOMY 

V. IMPACT OF OTHER AUTOMOTIVE DESIGN FEATURES ON FUEL ECONOMY 

VI. FUTURE TRENDS IN FUEL ECONOMY 

VI I. SUMMARY 

VII !.CONCLUSIONS 
I. INTRODUCTION 

This paper analyzes the effect on fuel economy of emission controls 

on automobiles. The analysis examines the various vehicle design factors, 

including emission control devices, which affect motor vehicle fuel economy 

and discusses the impact of the individual variables. Fuel penalties which 

may be associated with emission control systems are placed into the perspective 

of other fuel penalties which are currently, or may in the future, be experienced 

by the motoring public. 

No attempt is made here to deal with the question of national petroleum 

consumption. However, this analysis provides a part of the necessary input 

for such a study. 

l! II. DEFINITION OF "FUEL ECONOMY" 

There are many ways to report the fuel economy of automobiles. Miles 

per gallon (MPG) is the most commonly used and will be used in this analysis. 

All figures reported in this analysis are in terms of miles per gallon 

over the Federal Driving Cycle (see Section III. C.) While the single 

parameter, miles per gallon, is easily understood and a good measure of 

fuel economy, it must be qualified. Many factors influence fuel economy, 

and a knowledge of these factors is needed if valid comparisons of fuel 

economy figures are to be made. 

III. FACTORS AFFECTING FUEL ECONOMY 

The fuel economy of in-use light duty vehicles can range between 50 

and 5 mpg. The major factors that influence fuel economy and account for 

this wide spread are discussed below. 
3 

A. The Design of the Automobile 

The most important parameters associated with automobile design include 

vehicle weight, rolling resistance (including tire, driveline and aerodynamic 

drag) and axle ratio. Higher weight usually means poorer fuel economy because 

more work is required to move the vehicle. Higher rolling resistance usually 

means poorer fuel economy because more work is done deforming the tires and 

pushing the vehicle through the air. A higher (numerically) axle ratio usually 

means poorer fuel economy because the engine revolutions per mile are greater. 

For modern vehicle design, however, weight is the single most important parameter. 

B. The Manner In Which The Vehicle Is Driven 

This factor is both important and difficult, if not impossible, to quantify. 

In general, given identical vehicles, the driver who drives "harder" will get 

poorer fuel economy than the driver who drives less hard. Examples of "hard" 

driving are accelerating at or near the maximum capability of the vehicle, high 

cruise speeds, not driving smoothly, and racing the engine at idle. The magnitude 

of the effect due to the driver can be great, but there is no data on which to 

quantify this factor. 

C. The Type Of Route Traveled 

The best fuel economy achievable with automobiles is at constant speed 

cruise between 20 and 50 miles per hour in high gear. The exact optimum speed 

depends on the vehicle and engine type. However, no realistic driving is done 

at such a constant speed. Driving in heavy intracity traffic with many stops 

per mile, long idling periods, and low average speeds generally results in the 

poorest fuel economy. Driving on the highway at a constant speed usually results 

in better fuel economy. For this reason, many references to vehicle fuel economy 

also refer to the type of route traveled. Usually the distinction is made 

between city or 11 around town .. type of route; and "highway" type routes. 
All fuel economy figures reported in this analysis were measured 

using the Federal Driving Cycle - an urban driving route. This was 

done in part because it is the only cycle on which there is consistent 

data. However, the cycle is useful for this analysis because it is 

4 

representative of a significant portion of vehicle operation, in particular 

the driving done in urban areas. 

D. The Engine 

The design of the engine, its calibration, state of tune and overall 

mechanical condition affect fuel economy. Important design factors include 

compression ratio, intake and exhaust system configuration, internal 

friction and carburetor design. The calibration of the engine, its spark 

advance curve, the flow curve for the carburetor and the operation of 

the choke can all affect fuel economy. The state of tune of the engine 

as well as the condition of the parts that are usually involved in a tune up 

are important. Finally, the mechanical condition of the engine, especially 

valves and piston rings, can also hurt fuel economy if it is poor. 

Emission controls have affected both the design and calibration of 

engines. The design of the combustion chamber, the compression ratio, 

the spark advance curve and the carburetor calibrations have all been changed . . In addition, other devices like air pumps and exhaust gas recirculation 

have been added as emission control devices. All of these changes can have 

an effect on engine efficiency and, in turn, fuel economy. 

E. FUwer and Convenience Accessories 

M?ny power and convenience accessories are used on modern automobiles, 

including air conditioniflg, automatic transmissions, power steering, power 

brakes, power seats and heated windows. Although all of the devices use 
5 

energy which eventually results in fuel usage, the effect on fuel economy 

of all but two are negligible. The two important ones are air conditioning 

and automatic transmissions. 

The use of air conditioning lowers fuel economy. The extent to which 

it degrades fuel economy depends on how often the device is used, and how 

much cooling load is required of it. 

An automatic transmission is not as efficient as a manual transmission. 

However, whether a vehicle equipped with an automatic transmission shows 

better or worse fuel economy than a comparable manual transmission vehicle 

depends on the way in which each vehicle is driven. All other things being 

equal, the manual transmission equipped vehicle will generally show better 

fuel economy. 

F. Ambient Conditions 

The ambient temperature, humidity, pressure (altitude), and wind speed and 

direction all affect fuel economy. However, except in the case of large variations 

from standard conditions (e.g. cruising into a strong headwind or operating at 

a very high altitude,) the fuel economy effects of ambient conditions are minor. 

IV. EMISSION CONTROL EFFECTS ON FUEL ECONOMY 

There are, theoretically, two different ways to assess the effects 

of emission control devices on fuel economy. One way is to determine 

the effect of any one modification (e.g. retarded spark) on fuel economy. 

This could be expressed as a percentage loss or gain, and the total effect 

on a vehicle employing many modifications might be derived from adding up 

all the individual device effects. This approach is not correct because 

the effects are not, in general, additive. When one control approach or 

device is used in combination with other devices as part of a total system, 

there are various synergistic effects which can either lessen or worsen 

the impact on fuel economy of any one device. 
6 

The other approach, which is employed in this analysis, is to use actual 

vehicle test data and from this data determine the effect of the complete 

emission control system on fuel economy. While this approach does not provide 

data on the effect of individual emission control components, it does yield 

valid data on the complete system•s performance, which is the ultimate concern 

to the automobile user. 

The choice of the test technique and of the type of data used in 

making this kind of analysis are important. To validly compare fuel economy 

figures so as to determine the effect of some change in vehicle design or 

construction (emission controls in this case) the test must hold constant 

all (or as many as possible) of the factors that influence fuel economy other 

than the factor under study. 

A. Use of the Federal Test Procedure 

As indicated in Section III. C, the test used in this analysis to 

derive the fuel economy figures is the Federal Emission Test Procedure, 

involving an urban driving route run on a chassis dynamometer under controlled 

.temperature conditions. The advantages and disadvantages of using this procedure 

are summarized below. 

1. Advantages 

a. Ambient conditions are closely controlled, thus eliminating 

variability associated with this factor. 

b. Exactly the same route is used every time. The vehicle must 

be driven over the same speed-time trace each time for the 

emission test to be valid. This eliminates variability in 

two factors: the route, and the driver. 

c. The weight of the vehicle is known. Since the test procedure 

involves testing vehicles at a discrete inertia weight, the 

weight is known for every'test and can be isolated as a factor. 
2. Disadvantages 

a. Since the driving cycle is an urban one, it is not possible 

to compute a "highway" fuel economy figure. 

b. The rolling resistance of the dynamometer used in the test 

differs slightly from actual on-the-road rolling resistance. 

These drawbacks do not, however, prevent valid comparisons regarding 

urban fuel economy or the overall fuel economy potential of various engine 

systems or engine/vehicle modifications. In addition, the measurement of 

CO and co2 and miles traveled during the test provides an accurate and 

repeatable method ~ of calculating fuel economy. 

B. Data Sources 

The data used as input for this study came from three major sources: 

EPA surveillance data, EPA certification data, and EPA inhouse data from 

various test and evaluation programs. 

Use of the surveillance data of older cars can be challenged due to 

the fact that the older in-use vehicles may not be directly comparable to 

the 1973 certification prototypes, or to the advanced catalyst equipped 

prototypes, due to the possible effects of maintenance and mileage on fuel 

economy. It is, however, the only consistent data which exist for the earlier 

model years and until such time as data on the effects of accumulated mileage 

on MPG indicate otherwise, the aggregaton of all the data from the three sources 

is considered to be a valid assumption. 

C. Use of "C" Factor and Display of Data 

When the data are plotted as fuel economy (in MPG) versus inertia weight 

(IW) most of the data lies near the line represented by the equation 

MPG x IW = C, where "(11 is a constant va 1 ue for any given model year. In 

order to facilitate using a one parameter curve for each model year the 
8 

value "C" was calculated in such a way to minimize the squared error. In 

this way the effect of inertia weight can be eliminated and the value "C" 

becomes an indicator of the average fuel economy for that model year. The 

percent loss or gain in average fuel economy for each model year (all vehicle 

weights) can then be determined by comparing the "C'' values. 

The average MPG figures for the various model years/inertia weights are 

shown in Table I. Appendix I contains tables which give the detailed data 

on average MPG and the range of MPG for the different inertia weights in model 

years 1957-1973. Figure 1 is a plot of the curves for pre-68 cars and 1973 

cars as well as 75/76 prototypes and alternative engines. 
9 

TABLE I 

MPG vs INERTIA WEIGHT AND MODEL YEAR* 

Model INERTIA WEIGHT # of vehicles 

Year irl sarfl~l'e 

1750 2000 2250 2500 2750 3000 3500 4000 4500 5000 5500 

57 N.D. 26.5 N.D. N.D. N.D. N.D. 14.8 13.9 N.D. N.D. 12.9 24 

58 N.D. 26.2 19.5 N.D. 13.4 N.D. 14.2 14.4 12.8 10.1 N.D. 23 

59 N.D. 29.4 N.D. N.D. N.D. 15.7 15.2 14.1 13.4 13.9 N.D. 25 

60 N.D. 20.3 N.D. 22.8 24.4 N.D. 16.0 13.4 11.0 11.1 N.D. 19 

61 N.D. 30.3 N.D. 21.1 17.6 18.2 13.1 13.5 10.6 N.D. N.D. 26 

62 N.D. 29.9 N.D. N.D. 18.9 17.2 15.7 15.0 12.4 11.2 N.D. 51 

63 N.D. 25.0 20. 1 19.2 16.7 15.9 13.7 12.8 11.5 10.7 N.D. 76 

64 N.D. 24.1 N.D. N.D. 17.6 17.0 14.6 14.0 11 .5 11 .0 N.D. 94 

65 N.D. 23.5 N.D. N.D. 19.0 16.7 14.5 13.4 13.2 10.6 N.D. 137 

66 N.D. 24.6 N.D. N.D. 15.2 14.7 14.3 13.3 12.4 13.0 9.3 102 

67 N.D. 24.7 30.6 N.D. 18.8 15.4 13.8 12.5 12.3 11.7 10.3 92 

68 N.D. 21.5 20.8 19.3 19.5 15.4 13.3 12.1 11.6 8.8 N.D. 106 

69 N.D. 23.1 20.4 19.7 N.D. 15.8 13.4 11.8 11.5 9.8 11.6 163 

70 N.D. 24.5 21.1 17.8 18.9 15.6 13.5 12.1 10.9 10.2 9.7 287 

71 27.4 21.9 21.2 19.6 18.5 15.2 13.0 11.3 10.6 9.3 8.1 148 

72 N.D. 25.7 21.3 18.0 21.7 15.6 14.0 11.2 10 .l 9.3 8.7 84 

73 N.D. 25.5 20.7 19.9 17.9 16.2 14.0 11.2 10. 1 9.4 8.8 630 

*MPG figures for early model years (57-62) are based on limited data. This 

is partly responsible for the wide scatter in this early·data. 

N.D. - No Data 
io 

D. Effect of Emission Control on Fuel Economy 

Many things can be inferred from the mass of data. What has been 

done here is to compare 11C11 values for each model year. The fuel economy 

penalties in terms of the constant 11C11 for model years 68 thru 73 are 

listed below. 

TABLE II - Effect of Emission Control on Fuel Economy 

Model Year 11C11 Value Fuel Econom~ Loss 

(%of Uncontrolled) 

57-67 (Uncontrolled) 52129 None (baseline) 

68 47108 9.6 

69 47891 7.9 

70 48320 7.3 

71 47009 9.8 

72 49362 5.3 

73 48667 6.6 

Average loss 68-73, 7.75% 

The penalty due to emission controls as expressed above is far from the 

only cause of the increase in national automotive fuel consumption and can 

not be compared with total fuel consumption on a one for one basis. Factors 

such as increasing car population, the relative number of miles driven by 

controlled and pre-controlled cars, and the varying distribution of vehicle 

weight in each model year also have to be taken into account. These factors 

were not analyzed in this study and thus no concl~sions concerning total 

nationwide impact on fuel consumotion are drawn. 
11 

E. Effect of Compression Ratio Changes 

General Motors vehicles went to lower compression ratios across the 

board in 1971, and others have since done the same. To isolate the effect 

of compression ratio, data from one-hundred and seventeen 1970 and fifty-five 

1971 GM cars of varying weight were examined. 

Model Year 

70 

71 

TABLE III - Effect of Lower Compression Ratio, in MPG 

3500 lb 4000 lb 4500 lb 5000 lb 5500 lb 

13.7 11.4 10.4 9.9 8.5 

13.6 11.5 10.7 9.6 8.1 

The fuel economy was worse in three weight classes, and better in two. 

These data do not demonstrate that lowering compression ratio had any effect 

on vehicle fuel economy. 

V. IMPACT OF OTHER AUTOMOTIVE DESIGN FEATURES ON FUEL ECONOMY 

To provide an appropriate perspective the data presented above need to 

be related to other fuel economy penalties being experienced in today's cars. 

A. Air Conditioning 

EPA laboratory tests of air conditioned full sized cars with and without 

the air conditioner operating show a 9% loss in fuel economy over the Federal 

driving cycle in a 70 degree F ambient temperature. This penalty can go as 

high as 20% (based on compressor hp calculations) for continuous use on a 

hot day in urban traffic. The penalty can obviously, also, be very low or zero 

when air conditioning is used little or not at all .. The 9% loss measured in 

the EPA tests is approximately midway between these limits and is considered 

representative. 
B. Automatic Transmissions 

The fuel economy penalty associated with the use of automatic 

transmissions (AT•s) is difficult to quantify. There are many types 

12 

of AT•s (different numbers of speeds, and different operating principles). 

The same engine will be tuned differently for use with an AT than for use 

with a manual transmission, and different rear axle ratios are used with 

AT•s to optimize their performance. All of this compounds the problem of. 

identifying the impact of AT 1s on fuel economy. Periodicals on the subject 

of vehicle performance have reported fuel penalties of 10% for AT 1

s. On 

the other hand, as indicated earlier, an AT may in certain circumstances improve 

fuel economy. EPA does not have independent data on this question. In view 

of all the available data, EPA concludes that the fuel economy penalty of 

5% to 6% reported by General Motors in public hearings in April 1972 is 

representative. 

By comparing the fuel economy penalties of an automatic transmission or 

air conditioning with the penalty attributable to emission controls, it can 

be seen that the loss due to emission controls through the 1973 model year 

is about the same size as the penalty incurred due to use of convenience 

devices such as air conditioning or automatic transmissions. 

C. Vehicle Weight 

The fuel economy loss associated with emission controls is significantly 

less than that many vehicle operators claim they are experiencing. One major 

reason for this is that much of the decreased fuel economy observed is in fact 

attributable to the phenomenon of nameplate weight growth. When a nameplate, 

(Chevorlet Impala, for example) is first introduced, it identifies a vehicle 

weighing a certain amount. Over the years however, vehicles with the same 
13 

nameplates have typically become heavier, a trend often unnoticed by the 

vehicle operator. The data in Table I and in Appendix I indicates the 

dramatic influence of weight on fuel economy. If one only compares the fuel~ 

economy of vehicles with the same nameplate (but different weights,) a 

conclusion regarding the impact of a non-weight parameter (such as emission 

control) on fuel economy will be wrong. The following example shows this 

effect: 

TABLE IV - Effect of Vehicle Weight Growth on Fuel Economy 

YEAR 

1958 

1973 

CAR WEIGHT 

4000 lb 

5500 lb 

NAMEPLATE 

Chevorlet Impala 

Chevorlet Impala 

MPG 

12.1 

8.5 

In this case, the additional 1500 lbs is predominatly responsible for 

the loss in fuel economy, not the emission controls. 

VI. FUTURE TRENDS IN FUEL ECONOMY 

A. The 1975/1976 Emission Control System 

Very little valid or consistent data exists on fuel economy of 75/76 

prototypes. Although some loss may be expected with the use of certain emission 

control techniques, the small amount of data available to EPA does not yet 

demonstrate any trends. This lack of trends is further supported by recent 

(Nov. 1972) reports from several large auto manufacturers who report no difference 

in the fuel economy of their 1975 prototypes and 1973 vehicles of the same 

weight. 
14 

TABLE V - Comparison of Fuel Economy of 1975/76 Prototypes with 1973 Vehicles 

Vehicle Type Inertia Weight # of Tests Prototype Fuel 1973 Vehicles 

Economy Average Range 

75 Prototype 4000 1 10.0 11.2 7.7-14.6 

75 Prototype 4500 3 10.7 10. 1 7.4-13.6 

75 Prototype 5000 1 9.3 9.4 7.6-11.8 

75 Prototype 5500 l 6.9 8.8 7.1-10.0 

76 Prototype 5000 1 8.6 9.4 7.6-11.8 

76 Prototype 5000 1 9.5 9.4 7.6-11.8 

76 Prototype 5000 1 6.6 9.4 7.6-11.8 

See also Figure 1. 

Based on the limited data available from 75/76 systems, the only thinq 

that can be said is that a trend toward better or worse fuel economy has not 

been demonstrated at this time. 

B. Future Weight Trends 

Vehicles have historically been getting heavier. Any influences which 

causes the weight to go up will reduce fuel economy. A major factor is the 

potential increase in vehicle weight due to future safety standards. The 

target weight for the Department of Transportation Experimental Safety Vehicle 

(ESV) was 4200 pounds. Automotive Engineering, September 1972 P.32, reports 

that the prototype vehicles had weights of 4900, 5300, 5400, and 5800 pounds . 

. If future vehicles in the standard size class increase as much as these 

prototypes (700 to 1600 lb) - fuel economy will suffer. As a hypothetical 

example, increasing the weight of the average 1973 4000 lb vehicle to 5000 lb 

could mean a drop in fuel economy from 11.2 to 9.4 MPG, a 16% fuel economy penalty. 

C. Future New Engines 

1. Rotary Engine 

While many engines are being investigated as replacements for the conventional 

spark-ignition, reciprocating engine, the one with the highest potential for near 

term use is the rotary, or Wankel, engine. Despite the recent increase in publicity, 

the Wankel is not a newly developed engine. It has been under development for over 

20 years and in production for over 5 years by certain foreign manufacturers. 
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All 1973 Cars 

Pre-controlled Cars 

(average 57-67) 

FIGURE 1 

FUEL ECONOMY VS VEHICLE WEIG~i 

Federal Driving Cycle 0 - 75 Prototypes vehicles - 76 Protot es vehicles 

~ 1973 Diesel 

(Mercedes-220D) 

\ 

Protot~ee · · Strati 1ed Charge (Capri) 

1973 Rotary Engi~ 

~---------t-----------t----------+------------·--------

Vehicle Inertia Weight (pounds) 
The data available to EPA on fuel economy of rotary engine vehicles 

is presented below and compared to data on 1973 vehicles of the same weights 

but equipped with conventional reciprocating engines. See also Figure 1. 

TABLE VII - Comparison of Rotary Engine Fuel Economy With 1973 Vehicles 

Inertia Weight Rotary Engine 1973 Vehicles 

Vehicle Average Range 

2250 14.6* 20.7 18.9 to 21.9 

2500 13.3 19.9 13.3 to 23.7 

2750 12. 1 17.9 11.9 to 23.7 

2750 12.3 17.9 11.9 to 23.7 

2750 11.9 17.9 11.9 to 23.7 

3000 14.9* 16.2 13.6 to 19.7 

*Not 1973 vehicles. 

The rotary engine fuel economy results are consistently at or near the 

16 

bottom 

of the range in each weight class and are significantly below the average. The 

fuel economy data on the 1973 rotary engine vehicles represents a 35% loss in 

fuel economy when compared to the average for the same weight vehicles equipped 

with conventional engines. Historically, engines have improved in performance 

as their development continues and their use increases. Whether this will be 

the case with the fuel economy. of the rotary engine is not known. 

2. Diesel Engine 

The Diesel engine is the only engine other than the gasoline, sparkignition, rotary and reciprocating engines that is being used commercially 

in significant numbers in passenger cars in this country (approximately 

6000 are imported each year). The Diesel, however, is not a new engine. It 

has been used in trucks for over 30 years and is widely used in passenger cars 

in Europe. The data available to EPA on the fuel economy of a diesel engine 

vehicle are shown below, and compared to that on 1973 vehicles of the same 

weight equipped with conventional engines. 
17 

TABLE VIII - Comparison of Diesel Enqine Fuel Econom~ With 1973 Data 

Inertia Weight Diesel All 1973 Vehicles 

Average Ranqe 

3500 24.7 14.0 9.8 to 17.8 

The Diesel (which in this case met the emission levels required by the 

standards) achieved 75% better fuel economy than the average 1973 vehicle 

of the same weight equipped with a conventional engine. See also Figure 1. 

3. Other Engines 

In addition to the Wankel and Diesel, several other engines are being 

considered as replacements for the gasoline, spark-ignition, reciprocating 

engine. These include stratified charge, Stirling, Rankine cycle and gas 

turbine engines. 

For these engines, valid data exists for only the stratified charge 

engine. At an inertia weight of 2,500 pounds, a vehicle equipped with a 

stratified charge engine (which in this case met the emission levels, at 

low mileage, required by the 1976 standards) demonstrated fuel economy of 

about 23 miles per gallon or 12% better than the average 1973 vehicle of 

that weight. See Figure l. Valid data on the fuel economy of the other 

possible engines is not available at this time. 

VI I. SUMMARY 

The EPA has analyzed fuel economy data from more than 2000 cars (of 

which over 1400 were equipped with emissions controls) tested on the Federal 

Driving Cycle. 

1975 
18 

The data were derived from certification, surveillance and inhouse 

evaluation testing. This is the most extensive data analysis known to have 

been.performed on this subject to date. It is also considered to be the 

most accurate for the purpose of comparing vehicle design parameters because 

of the use of a single consistent driving cycle and controlled ambient conditions. 

The study indicates that vehicle weight is the single most important vehicle 

design parameter affecting fuel economy. Past and future increases in vehicle 

weight have had, and will continue to have, a significant adverse effect on fuel 

usage. Weight is a parameter over which the car buyer has direct discretionary 

control. 

The average fuel economy loss due to emission control for 1968-1973 vehicles 

is less than 8%. This penalty is approximately equal to the penalty associated 

with the use of convenience devices such as air conditioning or automatic 

transmissions. Despite the many statements reg~rding the loss in fuel economy 

due to meeting the 1975/1976 standards, no significant trend has yet developed 

in the data available to EPA. EPA will continue to gather data on 75/76 prototype 

with the aim of making a more definitive statement in the future. 

The use of engines other than the present spark-ignition, reciprocating 

engine could have a significant impact on vehicle fuel economy. Use of the 

spark-ignition, rotary engines presently results in significant losses in 

fuel economy, while the Diesel engine offers a significant increase in fuel 

economy. 

VIII. CONCLUSIONS 

1. Vehicle weight is the single most important parameter affecting 

urban fuel economy; a 5000 pound vehicle demonstrates 50% lower fuel 

economy than a 2500 pound vehicle. 
19 

2. The fuel economy loss for 1973 vehicles, compared to uncontrolled 

(pre 68) vehicles, is less than 7%. The average fuel economy loss due 

to emission control for all controlled (68-73) vehicles is 7.7%. 

3. The fuel economy penalty due to the use of convenience devices such 

as air conditioning or automatic transmission is roughly equal to the 

penalty due to emission controls. 

4. No trend is shown for fuel economy for 1975 and 1976 vehicles at 

this point in time. More data are needed. 

5. Data on 172 1970 and 1971 GM cars did not demonstrate any effect 

on fuel economy of reduced compression ratio. 

6. Future trends, including increased vehicle weight and possible use 

of the rotary engine, may result in a significant (20%-35%) fuel economy 

penalties. 

7. The Diesel and stratified charge engines show better fuel economy 

then the conventional engine with the Diesel showing a fuel economy 

improvement of more than 70%. 

8. Today•s car buyer has available a choice of vehicles in terms of the 

size and weight, engine type, and convenienGe devices. These choices 

can influence a vehicle•s fuel economy over a range of 4 to 1 (See 

Range of Data in Appendix I). 
20 

FOOTNOTES: 

1/ Fuel economy should not be confused with fuel consumption which is expressed 

1n terms of gallons of fuel consumed per mile. One is the inverse of the other. 

A certain percentage increase or decrease in fuel economy does not equal the 

same percentage decrease or increase in fuel consumption. For example, one car 

getting 20 MPG has 33% better fue 1 economy than one with 15 ~1PG. However its 

fuel consumption is 25% less. The two terms cannot be used interchangeably. 

?J Calculation of Fuel Economy 

Since both CO and C02 are measured for the test, an approximate carbon balance fuel economy figure can be generated from the CO and 

co2 data. The formulae used are: 

72 FTP MPG = 2360 . 42-:--9 ..... (~co~);..:,.+-=---.=27=2~( c=o~2 ).--

Where the dimensions of CO and co2 are grams per mile for the complete test. 

75 FTP MPG = 17800 -. 4....,.2=9 ..:....;(,..,..c.,;:,.;o ),___+ -.-=27=2..---r:( c"""o,__ 2 ) 

Where the CO and the C02 are the total number of grams of CO and co2 in 

Bags 1 and 2. 

Both of these formulae neglect the hydrocarbon contribution to the 

carbon balance. This however is not serious if the data are used for 

comparative purposes as is the case in this analysis. In addition, to 

the accuracy to which the data are reported, the neglect of the hydrocarbons 

influence is not important. 

The accuracy of any single data point is believed to be within + 5% 

of the true value. This is the maximum inaccuracy in the co2 measurement. 

The accuracy of the mean or average values is believed to be much higher 

since the experimental errors are random and tend to cancel out in the 

sample. No statistical analysis has been performed on this data. The data 

and conclusions presented on the preceding pages are based only on the 

observed means of the samples. 
A-1 

APPENDIX I 

Inertia Weight Average MPG Range # of Data Points 

Model Year 1973 c = 48667 

2000 25.5 23.7 to 28.5 6 

2250 20.7 18.9 to 21.9 8 

2500 19.9 13.3 to 23.7 74 

2750 17.9 11.9 to 23.7 62 

3000 16.2 13.6 to 19.7 37 

3500 14.0 9.8 to 17.8 64 

4000 11.2 7.7 to 14.6 69 

4500 10.1 7.4 to 13.6 157 

5000 9.4 7.6 to 11 .8 96 

5500 8.8 7.1 to 10.0 57 

Model Year 1972 c = 49362 

2000 25.7 21.4 to 37.8 5 

2250 21.3 18.5 to 27.8 5 

2500 18.0 17.0 to 19.0 2 

2750 21.7 13.0 to 41.7 10 

3000 15.6 10.1 to 20.6 7 

3500 14.0 10.7 to 19.2 5 

4000 11.2 6.3 to 15.3 28 

4500 10. 1 8. 5 to 11 .3 8 

5000 9.3 7.8 to 10.6 11 

5500 8.7 7.8 to 9.2 3 

Model Year 1971 c = 47009 

1750 27.4 1 

2000 21.9 19.3 to 23.9 6 

2250 21.2 18.7 to 27.0 11 

2500 19.6 14.7 to 25.0 16 

2750 18.5 16.8 to 21.9 6 

3000 15.2 7.8 to 20.7 10 

3500 13.0 8.9 to 20.2 15 

4000 11.3 8.8 to 13.6 42 

4500 10.6 7.8 to 12.7 30 

5000 9.3 5.4 to 15.4 10 

5500 8.1 1 

Model Year 1970 c = 48320 

2000 24.5 20.2 to 32.0 8 

2250 21.1 13. 1 to 40. 1 7 

2500 17.8 10.9 to 22.1 11 

2750 18.9 15.8 to 20.2 9 

3000 15.6 11 . 5 to 22.4 21 

3500 13.5 9.4 to 17.7 65 

4000 12. 1 8.5 to 15.6 78 

4500 10.9 7.3 to 13.3 51 

5000 10.2 6.6 to 13.4 30 

5500 9.7 8.3 to 12.2 7 
A-2 

Inertia Weight Average MPG Range # of Data Points 

Model Year 1969 c = 47891 

2000 23.1 15.3 to 26.0 14 

2250 20.4 17.8 to 24.4 4 

2500 19.7 18.1 to 26.8 13 

3000 15.8 10.5 to 19.8 13 

3500 13.4 9.8 to 17.4 37 

4000 11.8 9.0 to 15.4 43 

4500 11.5 9.1 to 21.2 31 

5000 9.8 8. 7 to 11 . 7 6 

5500 11.6 10.2 to 12.9 2 

Model Year 1968 c = 47108 

2000 21.5 19.9 to 23.6 8 

2250 20.8 1 

2500 19.3 1 

2750 19.5 1 

3000 15.4 11.9 to 19.8 15 

3500 13.3 9.5 to 25.0 29 

4000 12. 1 8.8 to 14.8 31 

4500 11.6 9.1 to 14.2 18 

5000 8.8 8. 7 to 8.9 2 

Model Year 1967 c = 54170 

2000 24.7 20.0 to 33.0 8 

2250 30.6 1 

2750 18.8 17.9 to 19.7 2 . 

3000 15.4 13.0 to 17.1 5 

3500 13.8 11.5 to 18.6 21 

4000 12.5 8.4 to 19.7 36 

4500 1Z.3 9.7 to 13.4 16 

5000 11.7 10.7 to 12.1 2 

5500 10.3 1 

Model Year 1966 c = 48934 

2000 24.6 20.5 to 31.2 6 

2750 .15. 2 l 

3000 14.7 12.0 to 16.9 16 

3500 14.3 10.0 to 20.7 25 

4000 13.3 8.6 to 28.8 34 

4500 12.4 9.8 to 15.5 16 

5000 13.0 10.9 to 16.9 3 

5500 9.3 1 
A-3 

Inertia Weight Average MPG Range # of Data Points 

Model Year 1965 c = 50581 

2000 23.5 19.0 to 27.5 4 

2750 19.0 16.4 to 21.2 8 

3000 16.7 10.9 to 21.9 18 

3500 14.5 8.4 to 21 .8 42 

4000 13.4 9.5 to 19.7 46 

4500 13.2 7.4 to 27.8 15 

5000 10.6 10.1 to 11.0 4 

Model Year 1964 c = 50259 

2000 24.1 22.1 to 26.6 3 

2750 17.6 16.3 to 20.5 8 

3000 17.0 14.3 to 20.9 21 

3500 14.6 10.2 to 29.8 28 

4000 14.0 9.6 to 30.4 19 

4500 11.5 8.6 to 15.5 12 

5000 11.0 10.2 to 11 . 6 3 

Model Year 1963 c = 48209 

2000 25.0 22.3 to 27.2 3 

2250 20.1 1 

2500 19.2 1 

2750 16.7 14.4 to 21 . 2 8 

3000 15.9 10.5 to 20.1 15 

3500 13.7 6.0 to 19.0 19 

4000 12.8 9. 2 to 18.3 18 

4500 11.5 9.3 to 13.5 10 

5000 10.7 1 

Model Year 1962 c = 56105 

2000 29.9 25.8 to 38.0 4 

2750 18.9 17.1 to 20.6 2 

3000 17.2 13.3 to 20.1 9 

3500 15.7 13.2 to 18.6 10 

4000 15.0 9.4 to 18.6 19 

4500 12.. 4 10.5 to 14.3 5 

5000 11.2 10.2 to 12.1 2 
A-4 

Inertia Weight Average MPG Range # of Data Points 

Model Year 1961 c = 53672 

2000 30.3 1 

2500 21.1 19.9 to 22.2 5 

2750 17.6 12.0 to 21.3 4 

3000 18.2 17.5 to 18.9 2 

3500 13.1 8.7 to 17.5 2 

4000 13.5 10.5 to 17.1 9 

4500 10.5 9.6 to 12.3 3 

Model Year 1960 c = 52474 

2000 20.3 1 

2500 22.8 1 

2750 24.4 1 

3500 16.0 1 5. 1 . to 16.8 2 

4000 13.4 . 9. 9 to 17.9 11 

4500 11.0 10.6 to 11 .4 2 

5000 11.1 1 

Model Year 1959 c = 56386 

2000 29.4 18.7 to 44.2 3 

3000 15.7 15.3 to 16.1 2 

3500 15.2 14.4 to 16.1 3 

4000 14. 1 10.6 to 17.7 13 

4500 13.4 10.6 to 17.5 3 

5000 13.9 1 

Model Year 1958 c = 48095 

2000 26.2 1 

2250 19.5 1 

2750 13.4 1 

3500 14.2 ~ 1. 9 to 17.0 8 

4000 14.4 10.8 to 20.2 9 

4500 12.8 11.2 to 15.1 3 

5000 10. 1 1 

Model Year 1957 c = 54537 

2000 26.5 23.0 to 31.9 3 

3500 14.8 11.5 to 18.3 13 

4000 13.9 9.4 to 21 .6 7 

5500 12.9 1