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Average port area
The average cross-sectional area says a lot about how a split twin-cam channel flows and where it chokes. Enter the three station areas at the entry, the split and the throat, and we combine them into an average cross-sectional area in mm² and in².
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Average cross-sectional area
1 248,0 mm²
Station model for a split twin-port: the intake mouth is counted once, while the split and throat are counted for both valves. Measure the real areas in the channel.
How the calculation works
The model takes three representative cross sections along the channel and works out an average. The intake mouth is shared and counted once, while the split and throat exist in two copies, one per valve, and are therefore doubled. The sum of the three stations is then divided by three. The areas are given in mm² and the result is also shown in in² (1 in² = 645,16 mm²).
The average area is a way to compare channels and estimate air velocity together with the flow demand. An even area without sharp restrictions flows better than one that is wide in places and tight in others. Porting is about shaping the channel right, not just making it bigger. The real areas are measured in the channel itself.
Example
Entry 840 mm², split 777 mm² per channel and throat 675 mm² per valve give (840 + 2×777 + 2×675) / 3 = 1247,5 mm², that is about 1,93 in².
Guiding area ratios (of the throat area)
| Station | Share of throat area |
|---|---|
| Entry (mouth) | 110-115% |
| Split | 90-95% |
| Throat | 100% (reference) |
Guide values for a four-valve twin-cam channel. The actual areas are measured in the cylinder head.
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