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:
-
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
-
Swept volume in cubic ft/min. is the volume swept out by the pistons at each rpm.
-
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).
-
The friction mean effective pressure (fmep) is based on work by H. R. Ricardo published in “Handbook of Aeronautics”, Royal Aeronautical Society 1931.
-
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:
-
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
-
Swept volume in cubic ft/min is the volume swept out by the pistons at each rpm.
-
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).
-
The friction mean effective pressure (fmep) is based on work by H. R. Ricardo published in “Handbook of Aeronautics”, Royal Aeronautical Society 1931.
-
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.