This calculator applies a steady continuity-style velocity index to entered piston area, mean piston speed, effective valve curtain area, flow coefficient and sound speed. It does not predict valve choking, engine airflow or power.
Area and the velocity estimate
This calculator divides a nominal swept-volume-rate quantity by an assumed effective opening area. A smaller opening raises that velocity estimate, but the result does not supply the cylinder pressure history, gas density or valve timing needed to calculate actual engine airflow.
Inlet Valve Interactive Calculator
Explore an area-ratio velocity estimate, its sound-speed ratio and comparison with an arbitrary 0.60 reference index.
Equation Used
- Entered mean piston speed and piston area form a nominal swept-volume-rate index Ap cm.
- Entered curtain area and flow coefficient form an assumed effective area Ci Av.
- Entered sound speed is a user-supplied reference value.
- The 0.60 line is a chosen comparison reference, not a choking criterion or recommended operating limit.
- No crank-angle waveform, cylinder pressure, manifold/port/seat geometry, valve lift history, gas density/temperature/composition, pressure ratio, compressibility, wave action, discharge-coefficient map, volumetric efficiency, combustion, power, valve-train dynamics, stress or safety model.
The 0.60 reference is only a comparison line, not a physical choking threshold. Compressible choking depends on pressure ratio, gas state, geometry and unsteady flow; those quantities are not entered.
Continuity-style velocity index
Multiplying piston area by mean piston speed gives a nominal swept-volume-rate index. Dividing by entered flow coefficient times entered curtain area gives an inferred average velocity index.
The schematic illustrates a changing gap around a poppet. Its opening is not linked to the entered curtain area, and its flow lines do not represent calculated streamlines or velocity.
Compare the entered area and speed assumptions
The calculation can compare how entered area, speed and coefficient assumptions change a velocity ratio. It cannot select valve diameter or lift, predict choking, determine mass airflow, or estimate torque and power.
Velocity ratio, not a choking solution
Vindex=Ap cm/(Ci Av), with piston and curtain areas in compatible units. Dividing by entered sound speed gives a Mach-like index.
The remaining-span and reference-load tiles compare that index with 0.60 by arithmetic only. Sonic choking requires a compressible-flow pressure-ratio and thermodynamic model.
Worked example
For Ap=58.1 cm², cm=18.6 m/s, Ci=0.38 and Av=21.4 cm², the continuity velocity index is about 132.9 m/s. With a=340 m/s, the ratio is about 0.391, or 65.2% of the arbitrary 0.60 reference; remaining reference span is 34.8%.
What actual inlet flow depends on
Actual flow depends on valve lift and timing, port and seat geometry, pressure difference and gas state throughout the cycle. A measured flow coefficient also depends on its test conditions. These quantities are not solved here, so the displayed index cannot establish valve size, choking, engine power or durability.
Questions
Does an index above 0.60 prove the valve is choked?
No. The 0.60 line is not a physical choking criterion.
Is the velocity tile measured port velocity?
No. It is a lumped continuity-style index.
Can this predict engine power?
No. Mass flow, volumetric efficiency, combustion and losses are absent.
References & Further Reading
- Wikipedia contributors. Poppet valve. Wikipedia
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