The engine calculator asks for around sixty numbers: bore, stroke, rod length, compression ratio, four valve timing angles, the ramp and dwell that shape each valve's lift, valve and stem diameters, seat widths and angles, ignition timing, burn duration. Entering all of that correctly from scratch, in the right units and the right angle convention, is where most first attempts go wrong.

A preset gives you a complete, self-consistent set that already runs. Load the engine closest to what you are working on, confirm the result looks like the engine you know, then change one thing at a time and watch what moves. That is a far faster way to learn what the model responds to than starting from an empty form.

What the library covers

The presets span four groups: performance and tuning engines, production road engines, two-strokes, and industrial, marine and locomotive units. The range is deliberate — the same model has to hold up from a 52 mm motorcycle single to a 960 mm bore marine two-stroke, and having both in the library makes it easy to check that it does.

Two-strokes carry their own geometry: port heights, widths, entry angles and the scavenging arrangement instead of valve data. Loop-scavenged, uniflow with inlet ports, and uniflow with exhaust valves in the head are all represented.

How accurate are these numbers?

Each engine page shows the parameters the preset actually carries, computed from the preset itself rather than typed in separately, so a page can never advertise a number the calculator does not use. Where a manufacturer figure is quoted it is labelled as the reference value the preset was built against.

Some presets are approximations. Valve and port dimensions in particular are hard to source for older engines and are sometimes reasoned from bore size and the engine's class rather than measured. Treat a preset as a well-formed starting point, not as a factory data sheet — and if you have measured figures for an engine here, they will beat ours.

Timing angles use an absolute convention

One thing worth knowing before you compare a preset against a cam card: the valve angles here are absolute crank angles on a 0 to 720 degree frame, not the degrees-before-top-dead-centre convention a cam card uses. An intake that opens 20 degrees before top dead centre appears as 700, not as 20. The presets are the quickest way to see what a correct set looks like.