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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

Carb Size, CFM Calculator

Most factory, normally aspirated engines have an efficiency of about 80%. High performance tuning can increase it to close to 100%. To go beyond this requires a pressurised induction system like supercharging or turbocharging. The default entries below are from the glory days of the muscle car!

Enter Your Engine Information
Select Inches or CC? (1=CI 2=CC)   
Enter Engine Displacement   CI / CC
Enter Your Maximum Engine RPM   
Enter Volumetric Efficiency Of Engine   %
     
Required Carburetor Size In CFM
Carb CFM Required 100% VE
Carb CFM Required Your % VE
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

       For more calculators, CLICK HERE!


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