This chart will help you determine the size of the carburetor heat hose needed for alternate air and or the ram air inlet opening used to support engine induction air. The numbers represent the basic minimum requirement for that specific Engine RPM. At the bottom of the page you'll see a section that talks about millimeter size openings for a specific Cubic foot of air inlet.
Example: A Lycoming 0360 turning 2900 RPM will use 302 Cubic feet of air. The minimum size air inlet opening or sceet hose diameter to support this requirement is 33mm.
| CARBURETOR or THROTTLE BODY INLET REQUIREMENTS | ||||||||||
| 0235 Lycoming Cubic Foot Per Minute Air Requirements @ a given RPM | ||||||||||
| 235 | RPM | 2500 | 2600 | 2700 | 2800 | 2900 | 3000 | 3100 | 3200 | 3300 |
| CFM Usage Rate | 170 | 177 | 184 | 190 | 197 | 204 | 211 | 218 | 224 | |
| 0290 Lycoming Cubic Foot Per Minute Air Requirements @ a given RPM | ||||||||||
| 290 | RPM | 2500 | 2600 | 2700 | 2800 | 2900 | 3000 | 3100 | 3200 | 3300 |
| CFM Usage Rate | 210 | 218 | 227 | 235 | 243 | 252 | 260 | 269 | 277 | |
| 0320 Lycoming Cubic Foot Per Minute Air Requirements @ a given RPM | ||||||||||
| 320 | RPM | 2500 | 2600 | 2700 | 2800 | 2900 | 3000 | 3100 | 3200 | 3300 |
| CFM Usage Rate | 231 | 241 | 250 | 259 | 269 | 278 | 287 | 296 | 306 | |
| 0360 Lycoming Cubic Foot Per Minute Air Requirements @ a given RPM | ||||||||||
| 360 | RPM | 2500 | 2600 | 2700 | 2800 | 2900 | 3000 | 3100 | 3200 | 3300 |
| CFM Usage Rate | 260 | 271 | 281 | 292 | 302 | 313 | 323 | 333 | 344 | |
| 0540 Lycoming Cubic Foot Per Minute Air Requirements @ a given RPM | ||||||||||
| 540 | RPM | 2500 | 2600 | 2700 | 2800 | 2900 | 3000 | 3100 | 3200 | 3300 |
| CFM Usage Rate | 391 | 406 | 422 | 438 | 453 | 469 | 484 | 500 | 516 | |
| Carb inlet size MM | MAX Cubic FT carb Flow at 29.92 | |||||||||
| 23 | 213.25 | |||||||||
| 24 | 222.52 | |||||||||
| 25 | 231.79 | Basically this chart states that even a 35mm inlet will flow | ||||||||
| 26 | 241.06 | 325.50 CFM at sea level. The Lycoming 0320 only needs 306 | ||||||||
| 27 | 250.33 | CFM at 3300 RPM. | That gives the engine about a 7% buffer. | |||||||
| 28 | 259.60 | |||||||||
| 29 | 268.87 | I would want a 15 -20% buffer, a 38 to 42 mm allows that. | ||||||||
| 30 | 278.15 | |||||||||
| 31 | 287.42 | |||||||||
| 32 | 296.69 | |||||||||
| 33 | 305.96 | |||||||||
| 34 | 315.23 | |||||||||
| 35 | 324.50 | |||||||||
| 36 | 333.77 | |||||||||
| 37 | 343.05 | |||||||||
| 38 | 352.32 | |||||||||
| 39 | 361.59 | |||||||||
| 40 | 370.86 | |||||||||
| 42 | 389.40 | |||||||||
| 44 | 407.95 | |||||||||
| 46 | 426.49 | |||||||||
| 48 | 445.03 | |||||||||
| 50 | 463.58 | |||||||||
| 51 | 472.85 | |||||||||