What is CrankIt?

CrankIt is a free, interactive simulator of a 4-stroke V8 engine — specifically the 400 cubic inch V8 from a 1968 Pontiac GTO — and now its whole driveline. Everything on screen is driven by a live physical model: real crank-slider kinematics, measured camshaft lift curves, Wiebe-function combustion with a pressure–volume cycle, a friction-plate clutch and torque converter feeding real gear ratios, and an exhaust note synthesized by a physical waveguide model of the pipes — not a recording.

What you can do

Start the engine — key-on crank, catch, and settle to that lopey big-cam idle. Rev it with the throttle.
Three views: a single-cylinder cutaway with animated valves and flame front; a full V8 view that makes the 1-8-4-3-6-5-7-2 firing order and cross-plane rumble visible; and a drag-to-orbit 3D model of the whole rotating assembly.
Swap camshafts — stock, street, or race grinds, or fine-tune lift, duration, and lobe separation and watch (and hear) the idle, vacuum, and power band change.
Drive it — put it in gear: a Muncie 4-speed you shift yourself (with a money-shift guard) or a 4L80E automatic with a torque converter that creeps, multiplies torque at stall, shifts itself, and locks up in overdrive at ~2,050 rpm on the highway. Swap rear-axle ratios and hear every shift; the launch and acceleration match period road tests (~7 s to 60).
Read the diagrams — valve timing with overlap, the P–V loop, a torque & power dyno, the firing-order timeline, and a tractive-effort chart that shows why you shift where the gear curves cross.
Teach with it — slow motion, pause and scrub by crank degree, part labels, and 3D part toggles that hide the block, pistons, crank, valvetrain, or flywheel to show what's underneath.

Is it physically accurate?

Where it can be, it's exact: piston motion, valve events, the shared-crankpin 90° V8 geometry, the firing schedule, and the rpm↔speed relation through every gear are all computed, and every 3D part dimension derives from the documented engine spec (bore 4.12″, stroke 3.75″, 6.625″ rods, 10.75:1 compression — with real Muncie M20/M21 and 4L80E ratios and factory axle options). Where the model simplifies — like phenomenological volumetric efficiency or the managed clutch — the simplification is labeled in the app. It's an educational model first: honest about what's exact and what's illustrative.

Why a 1968 GTO 400?

Because it's the engine the author is learning to restore — and because a big cross-plane V8 with a lumpy cam is the most audible way to learn what camshaft overlap, manifold vacuum, and firing intervals actually do.