Performance Figures

7 Sep

TABLE OF PERFORMANCE FIGURES FOR A STANDARD MPJG ENGINE AT CR 6.5 (MG TA)

These values were back-calculated from the published bhp/rpm figures in the MG literature, “Tuning and Maintenance of MGs” by Philip H Smith and elsewhere.

imep = indicated mean effective pressure, bmep = brake mean effective pressure, fmep = friction mean effective pressure.

bmep = imep – fmep

rpm

bhp

Torque

lbs.ft

swept vol cfm

mix flow cfm

vol effy %

imep psi

fmep psi

bmep psi

1000

10.5

55.15

22.86

16.8

73.5

105.5

1500

15.7

54.97

34.30

25.1

73.3

118.3

13.2

105.1

2000

20.9

54.88

45.73

33.4

73.0

119.5

14.5

105.0

2500

26.0

54.62

57.16

41.6

72.8

121.0

16.5

104.5

3000

31.1

54.44

68.59

49.8

72.6

123.4

19.3

104.1

3500

36.1

54.17

80.02

57.8

72.3

126.3

22.7

103.6

4000

41.1

53.96

91.45

65.8

72.0

129.8

26.6

103.2

4800

45.0

49.24

109.70

72.0

65.6

125.1

30.9

94.2

5000

43.9

46.11

114.32

70.2

61.4

123.7

35.5

88.2

5400

40.0

38.90

123.46

64.0

51.8

113.4

39.0

74.4

Notes:

  1. Torque calculation: torque = bhp x 5252/rpm. Mixture flow calculation from various sources but agrees with the general statement that 100 bhp needs 160 cfm at 60 F and I atmospheric pressure, i.e. 45 bhp = 72 cfm

  1. Swept volume in cubic ft/min. is the volume swept out by the pistons at each rpm.

  1. Volumetric efficiency is from swept volume and mixture flow comparison but also checked against the equation from “Internal Combustion Engine Fundamentals”, J. B. Heywood, McGraw-Hill, 1988:

Vol effy (ev) = 2 x (mixture mass flow lbs/sec)/(inlet mixture density x engine displacement x revs./sec).

  1. The friction mean effective pressure (fmep) is based on work by H. R. Ricardo published in “Handbook of Aeronautics”, Royal Aeronautical Society 1931.

  1. The brake mean effective pressure was calculated from: bmep = 75.4 x 2 x Torque (lbs.ft)/Vd where Vd = engine displacement in cubic inches. Source: Heywood ibid.

TABLE OF PERFORMANCE FIGURES FOR A STANDARD XPAG ENGINE AT CR = 7.25

These values were back-calculated from the published bhp/rpm figures in the MG literature. Note that the calculated maximum torque and bmep figures do not agree with advertised data.

imep = indicated mean effective pressure, bmep = brake mean effective pressure, fmep = friction mean effective pressure.

bmep = imep – fmep

rpm

bhp

Torque

lbs.ft

swept vol cfm

mix flow cfm

vol effy %

imep psi

fmep psi

bmep psi

1000

10.56

55.46

22.12

16.9

76.4

110.0

1500

16.81

58.86

33.18

26.9

81.1

129.7

13.2

116.5

2000

22.84

59.98

44.24

36.5

82.5

133.3

14.5

118.8

2500

29.20

61.34

55.30

46.7

84.4

138.0

16.5

121.5

3000

35.56

62.25

66.36

56.9

85.7

142.6

19.3

123.3

3500

41.60

62.42

77.42

66.5

85.9

146.3

22.7

123.6

4000

46.55

61.12

88.48

74.5

84.2

147.6

26.6

121.0

4500

51.30

59.87

99.54

82.1

82.5

149.4

30.9

118.5

5000

54.31

57.05

110.60

86.9

78.6

148.5

35.5

113.0

5200

54.40

54.94

114.60

87.0

75.9

145.8

37.0

108.8

5500

52.58

50.21

121.66

84.1

69.1

139.8

40.4

99.4

6000

47.00

41.14

132.72

75.2

56.7

 

81.5

Notes:

  1. Torque calculation: torque = bhp x 5252/rpm. Mixture flow calculation from various sources but agrees with the general statement that 100 bhp needs 160 cfm at 60 F and I atmospheric pressure, i.e. 54.4 bhp = 87 cfm

  1. Swept volume in cubic ft/min is the volume swept out by the pistons at each rpm.

  1. Volumetric efficiency is from swept volume and mixture flow comparison but also checked against the equation from “Internal Combustion Engine Fundamentals”, J. B Heywood, McGraw-Hill, 1988:

Vol effy (ev) = 2 x (mixture mass flow lbs/sec)/(inlet mixture density x engine displacement x revs./sec).

  1. The friction mean effective pressure (fmep) is based on work by H. R. Ricardo published in “Handbook of Aeronautics”, Royal Aeronautical Society 1931.

  1. The brake mean effective pressure was calculated from: bmep = (bhp x 2 x 39600)/(Vd x rpm) where Vd = engine displacement in cubic inches. Source: Heywood ibid.

This efficiency diagram and the tables of performance figures for standard
MPJG and XPAG engines have kindly been supplied by John Saunders.


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