Free tools
Minimum port area (MCSA)
MCSA is the smallest port cross-sectional area that keeps the air velocity below a chosen limit at your maximum rpm. Enter the bore, stroke, rpm and a speed limit, and you get the minimum port area in square inches and square millimetres.
All tools
Minimum port area
1,599 in²
Minimum port area (MCSA) to keep the top speed at or below the chosen limit. Lower velocity gives better top end, higher velocity better low-end. The real port is measured and shaped on the spot, the figure is a starting point.
How the calculation works
The minimum port area grows with the cylinder's dimensions and the rpm, because a larger volume and more strokes per minute need more air, and it shrinks when you allow a higher air velocity. The formula uses bore and stroke in inches plus the rpm, with an empirical constant of 0,00353 that ties it all together. We convert your measurements from millimetres to inches for you.
The speed limit is a design choice. A lower limit gives a larger port that favours top-end power at high rpm, while a higher limit gives a smaller port with higher velocity that favours low-end and torque. The value is a starting point, the real port is measured and shaped with regard to valve size, port shape and taper.
Example
86 mm bore, 86 mm stroke, 7000 rpm and a limit of 600 ft/s give a minimum port area of about 1,60 in² (1031 mm²).
Speed limit and port character
| Speed limit | Character |
|---|---|
| Lower speed (approx 600 ft/s) | larger port, better top-end power |
| Higher speed (approx 700 ft/s) | smaller port, better low-end and torque |
Guide values. Also take valve size, port shape and taper into account when the port is sized.
More tools
Related services
Building for real? We take care of the job.
Common questions about minimum port area (mcsa)
Need help with your engine build?
Describe your project and we will get back to you within 24 hours. Quote after inspection.