Using the interface

The chart

The chart fills the main area. The horizontal axis is engine speed (RPM); the vertical axis is venturi diameter (mm). Each horizontal line is a commercial size: 10 mm, 12 mm, 14 mm, …, 60 mm.

Along each line, the color changes by RPM:

• vivid green / dark green: ideal — velocity sits inside the healthy band with margin from both edges (dark variant = outside the working band);
• cyan / dark cyan (carburetor only): acceptable — velocity is just above anemic and below ~60 m/s, the classical lower bound for solid carburetor signal. Injection has no cyan zone since atomization is injector-driven (dark variant = outside the working band);
• light blue / dark blue: low gas velocity at that RPM (carburetor too big);
• yellow / dark yellow: restrictive at that RPM (carburetor too small).

The line is thicker through the ideal RPMs and thinner through the rest, so the eye picks up the green segments first.

A legend below the chart pairs each color with its meaning, and shows the vivid-versus-dark contrast next to the "working regime" label.

If the parameters are invalid (e.g. displacement set to 0), the chart is replaced by a short message. Fix the value to bring it back.

The form

The form sits next to the chart (left sidebar on a wide screen, below on a phone) and is split into two sections.

Basic

• Engine type: motorcycle, car, kart, jetski, outboard, chainsaw, stationary or moped. Sets the broad RPM context the chart uses to color-code lines.
• Application: how the engine will actually be used, not its body style. A Honda CG is urban, not "naked"; a Harley is cruiser (highway, torque-optimized); an R1 is sporty on the road and track on a circuit. Most options are shared across motorcycle and car; a few are vehicle-specific (cruiser, hard enduro and motocross are moto-only; highway is car-only — same concept as cruiser, different label by convention). Disabled (not hidden) when the type has a single canonical application (e.g. stationary → synchronous).
• Induction: carburetor or electronic injection. Adapts the velocity tolerance and the labels of related fields.
• Displacement (cm³): engine total displacement.
• Number of cylinders.
• Number of carburetors / throttle bodies: total carburetor (or TBI) bodies. For a 4-cylinder with a single Weber, this is 1.

Advanced (collapsed by default)

Open the Advanced section to fine-tune:

• Application profile (K factor): stock, sport or competition variant for the chosen engine type. Higher K factors place the ideal venturi lower in the diameter range.
• Barrels per carburetor: 1 (most carburetors), 2 (DCOE, IDF, 2E).
• Firing interval: crank degrees between cylinder firings — active only when cylinders share a carburetor. Defaults to 180° (4-cylinder even firing). Use 360° for a classic British twin, 90° for a V8, etc.
• Boost pressure (bar): for blow-through turbo. 0 for naturally aspirated.
• Maximum volumetric efficiency: slider from 50% to 115%. Lowering it shrinks the diameter spread the chart considers; raising it pushes the upper edge higher (more breathing).

Top bar

The brand ("Afinados") links back to the tools hub. The theme toggle switches between light and dark; the choice is saved.