CrankIt

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.
• Four 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; a drag-to-orbit 3D model of the whole rotating assembly — with an optional ghost rolling chassis (frame rails, driveshaft, live axle, and four wheels at true speeds); and a driveline view that opens the transmission.
• See inside the gearbox — the driveline view draws the whole power path (engine → clutch or torque converter → gearbox → axle → wheel) with every shaft at its true speed: watch the clutch slip and lock on launch, the converter multiply torque at stall, and the synchro collars lock a gear — the Muncie is drawn with its real published tooth counts. Tap any part for a labeled close-up, or go fullscreen with just the throttle and shifter.
• 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).
• Break the tires loose — floor it from a stop and the rear tires light up: with 400 lb-ft on period bias-plies the grip runs out before the clutch does, so the wheels spin faster than the road and the car crawls on sliding grip until they hook up. The traction chart shows the grip ceiling the torque pokes through, the driveline view shows the rim spinning ahead of the road, and the 3D ghost chassis shows the rear wheels racing ahead of the fronts in a burnout.
• 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 — and the grip limit the tires can put down.
• 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 — or add the whole rolling chassis to see the power path to the road.

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; the driveline view even draws the Muncie's published gear tooth counts, which rebuild the documented ratios). Wheelspin comes from real weight transfer and a tire grip limit, calibrated so a wide-open launch matches the documented acceleration. Where the model simplifies — like phenomenological volumetric efficiency, the managed clutch, or the two-state (grip/slide) tire — 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.