Carburetor CFM Calculator and Guide
CFM Selection Chart / Volumetric Efficiency
assumed to be 100%
|
Engine
|
Maximum Engine RPM
|
C I D
|
1000
|
1500
|
2000
|
2500
|
3000
|
3500
|
4000
|
4500
|
5000
|
5500
|
6000
|
6500
|
7000
|
7500
|
8000
|
8500
|
9000
|
100
|
29
|
43
|
58
|
72
|
87
|
101
|
116
|
130
|
145
|
159
|
174
|
188
|
203
|
217
|
231
|
246
|
260
|
200
|
58
|
87
|
116
|
145
|
174
|
203
|
231
|
260
|
289
|
318
|
347
|
376
|
405
|
434
|
463
|
492
|
521
|
225
|
65
|
98
|
130
|
163
|
195
|
228
|
260
|
293
|
326
|
358
|
391
|
423
|
456
|
488
|
521
|
553
|
586
|
250
|
72
|
109
|
145
|
181
|
217
|
253
|
289
|
326
|
362
|
398
|
434
|
470
|
506
|
543
|
579
|
615
|
651
|
300
|
87
|
130
|
174
|
217
|
260
|
304
|
347
|
391
|
434
|
477
|
521
|
564
|
608
|
651
|
694
|
738
|
781
|
325
|
94
|
141
|
188
|
235
|
282
|
329
|
376
|
423
|
470
|
517
|
564
|
611
|
658
|
705
|
752
|
799
|
846
|
350
|
101
|
152
|
203
|
253
|
304
|
354
|
405
|
456
|
506
|
557
|
608
|
658
|
709
|
760
|
810
|
861
|
911
|
400
|
116
|
174
|
231
|
289
|
347
|
405
|
463
|
521
|
579
|
637
|
694
|
752
|
810
|
868
|
926
|
984
|
1042
|
425
|
123
|
184
|
246
|
307
|
369
|
430
|
492
|
553
|
615
|
676
|
738
|
799
|
861
|
922
|
984
|
1045
|
1107
|
450
|
130
|
195
|
260
|
326
|
391
|
456
|
521
|
586
|
651
|
716
|
781
|
846
|
911
|
977
|
1042
|
1107
|
1172
|
500
|
145
|
217
|
289
|
362
|
434
|
506
|
579
|
651
|
723
|
796
|
868
|
940
|
1013
|
1085
|
1157
|
1230
|
1302
|
525
|
152
|
228
|
304
|
380
|
456
|
532
|
608
|
684
|
760
|
836
|
911
|
987
|
1063
|
1139
|
1215
|
1291
|
1367
|
550
|
159
|
239
|
318
|
398
|
477
|
557
|
637
|
716
|
796
|
875
|
955
|
1034
|
1114
|
1194
|
1273
|
1353
|
1432
|
575
|
166
|
250
|
333
|
416
|
499
|
582
|
666
|
749
|
832
|
915
|
998
|
1081
|
1165
|
1248
|
1331
|
1414
|
1497
|
Calculate your own carburetor needs:
|
CID
|
x
|
RPM
|
/
|
3456
|
x
|
VE%
|
=
|
CFM
|
455
|
x
|
3000
|
/
|
3456
|
x
|
90
|
=
|
355
|
Notes: Most Street engines are capable of achieving only about 80% VE (Volumetric Efficiency). A modified street engine with ported heads, headers, intake and carburetor can achieve about 85% VE. With extensive head and valve work and a new cam an engine may reach 95% or even more. It's normally not possible to achieve VE's over 100% without some form of forced induction.
If using dual carburetors each carburetor should be of the same CFM as listed for a single carburetor above. In other words if using two four barrels double the CFM.
Rochester big block carbs tend to be over-rated by ~30 CFM.
The above chart represents the minimum CFM required, to support a certain cubic inch engine at the maximum RPM potential of that engine. The number represented on the chart does not account for obstructions such as air filters, or inaccurate CFM ratings found on some carburetors. Also note that the Buick engines tend to like a big carburetor.
Page information contributed by Bob K. Mando