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Valve flow limit
The throat area sets a ceiling for how much a valve can flow. Enter the throat area per valve and choose a flow factor, and we work out the theoretical maximum flow in CFM at 28 inches of water for both intake valves.
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Theoretical maximum flow
305,4 CFM
Theoretical maximum flow at 28 inches of water for both intake valves. The flow factor is empirical and gives a ceiling, not a measured value.
How the calculation works
The theoretical maximum flow is based on each square inch of throat area flowing a certain number of CFM at the test pressure of 28 inches of water. We convert the throat area from mm² to in² (1 in² = 645,16 mm²), multiply by the flow factor and then by two, since a twin-cam channel has two intake valves. The result is a ceiling, not a measured value.
The flow factor depends on how well the valve seat and channel are worked. A race port with an optimal finish sits around 146 CFM/in², while a milder street port sits lower. The factor is empirical and gives an idealised upper limit. Real flow we measure on the flow bench, port by port.
Example
A throat area of 674,82 mm² (about 1,046 in² per valve) with a factor of 146 gives 2 × 1,046 × 146 = 305,4 CFM at 28 inches of water.
Flow factor by work level
| Level | Flow factor |
|---|---|
| Race with optimal finish | 146 CFM/in² |
| High-performance street and strip | 142 CFM/in² |
| Street performance | 138 CFM/in² |
| Mild street | 136 CFM/in² |
Empirical guide values at 28 inches of water. Real flow is measured on a flow bench.
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