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Head flow analysis
How close to the theoretical ceiling does your head flow? Enter the throat area per valve and you get the theoretical maximum flow with a fixed factor of 146 CFM/in². Add a measured flow and we also work out the flow efficiency.
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Theoretical maximum flow
305,4 CFM
Theoretical maximum flow at 28 inches of water with a fixed factor of 146 CFM/in² (race finish). Enter a measured flow to see the efficiency.
How the calculation works
The theoretical maximum flow is worked out from the throat area the same way as the flow limit, but here the flow factor is fixed at 146 CFM/in², corresponding to a race port with an optimal finish. We convert the throat area from mm² to in² (1 in² = 645,16 mm²), multiply by 146 and by two for the two intake valves. That gives the upper limit at 28 inches of water.
If you enter a measured flow from a flow bench, we work out the flow efficiency, that is how much of the theoretical ceiling the head actually reaches. Stock ports often sit at 50 to 60 percent, modified ones higher and well-worked race ports around 70 to 80 percent. It is a good measure of how much a porting job has gained, and how much is left.
Example
A throat area of 674,82 mm² gives a maximum flow of 305,4 CFM. A measured flow of 260 CFM then gives an efficiency of 260 / 305,4 × 100 = 85,1 percent.
Guide values for flow efficiency
| Port level | Flow efficiency |
|---|---|
| Stock port | 50-60% |
| Modified | 60-70% |
| Race port | 70-80% |
| Pro level | 80%+ |
Efficiency against the theoretical ceiling with a factor of 146 CFM/in² at 28 inches of water.
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Common questions about head flow analysis
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