REDLINE

Browser-based engine simulator with realistic drivetrain physics, layered audio synthesis, turbocharger model, and a manual clutch transmission. Runs on desktop and mobile.

Try it live

Features

• Drivetrain physics — torque curve interpolation, constant-power throttle model (BeamNG-style), angular acceleration, rev limiter with tight fuel-cut hysteresis. Honda S2000 AP1 gearbox. Engine allows over-rev past redline (no damage modeled).
• Manual clutch — hold Shift/C to decouple engine from wheels. Shift gears while clutch is held, release to feel spring-damper engagement. Clutchless shifts also work for convenience (auto-engages spring-damper).
• Spring-damper clutch engagement — replaces instant RPM snap with torsional spring-damper coupling engine and wheel inertias. Oscillation frequency and damping emerge from physics per gear.
• Turbocharger — BeamNG-style exhaust energy model with spool lag, wastegate, compressor back-pressure, and blow-off valve. Boost adds torque proportional to manifold pressure.
• 13-layer engine audio — Web Audio API with frequency-band samples (low/mid/high) crossfading by RPM and throttle. Separate on/off-throttle sample sets, REV redline loop, limiter gated loop, transmission whine, 4-band decel layers, and synthesized shift thuds.
• Exhaust convolution reverb — procedurally generated impulse response from pipe geometry via ConvolverNode. Equal-power dry/wet crossfade.
• Per-cylinder variation — subtle timing jitter (±8%) and brightness/detune offsets per cylinder break mechanical perfection in both audio and visuals.
• Idle realism — idle air control holds RPM near 850, per-cylinder firing pulses add ±15 RPM flutter at ~14 Hz. Not a perfect flat line.
• Continuous throttle — 0–1 pedal position from keyboard (space = WOT), mouse drag, touch Y-position, or gamepad right trigger. Partial throttle blends on/off samples with volume scaling.
• Analog tachometer — DPR-aware canvas gauge with needle smoothing, redline arc, and glow. Responsive via ResizeObserver.
• Cylinder visualization — SVG cylinder bank with firing-order animations, per-cylinder brightness variation, and throttle-colored fills (orange = power, blue = engine braking). Supports inline-4, inline-6, and V6.
• Color token system — all colors in tokens.js + CSS custom properties. Canvas/SVG code imports JS tokens; stylesheets use var(--c-*).
• Responsive layout — works on desktop and mobile. Touch devices get on-screen clutch/shift/brake buttons and Y-axis throttle.
• Debug overlay — real-time bars for RPM (red on over-rev), speed, torque, throttle, boost, inertia, detune, clutch/engagement status, turbo spool, BOV, oscillation, audio band gains, and frame timing sparkline. Toggle with backtick.

Controls

Input	Action
Space	Full throttle (WOT)
Click + drag up	Proportional throttle (mouse Y)
Touch drag up	Proportional throttle
Shift / C	Clutch (hold to decouple, shift, release to engage)
Arrow Up / Down	Shift up / down (works with or without clutch)
S or B	Brake
Backtick (`)	Toggle debug overlay
Gamepad RT / LT	Throttle / brake
Gamepad LB	Clutch
Gamepad RB	Shift up
Gamepad Dpad Down	Shift down
Touch CLT	Clutch button
Touch BRK	Brake button

Getting Started

npm install
npm run dev

Open http://localhost:5173. Choose cylinder count and layout, then START ENGINE.

Tech Stack

• Svelte 5 with runes ($state, $derived, $effect, $props)
• Vite 6 + Cloudflare Vite Plugin
• Web Audio API (AudioContext, ConvolverNode, OscillatorNode)
• Canvas API / SVG
• Vitest for testing
• Cloudflare Workers for hosting (CD via GitHub Actions on tag push)

Project Structure

src/
├── App.svelte            — screen router (customizer → sim), global CSS tokens
├── Customizer.svelte     — engine config picker + audio loader
├── Sim.svelte            — main loop, input handling (keyboard/mouse/touch/gamepad)
├── Tachometer.svelte     — DPR-aware canvas analog gauge
├── CylinderBank.svelte   — SVG cylinder bank with firing-order animation
├── GearIndicator.svelte  — gear letter + speed display
├── Odometer.svelte       — distance counter (localStorage persistence)
├── DebugOverlay.svelte   — debug panel with bars, sparkline, status pills
├── engine/
│   ├── constants.js      — RPM limits, normalizeRPM()
│   ├── drivetrain.js     — physics: torque, gears, clutch, turbo, spring-damper
│   ├── audio.js          — 13-layer Web Audio engine + exhaust reverb + turbo whine
│   └── tokens.js         — color token system (JS exports + CSS vars)
│   └── __tests__/        — vitest test suites
└── main.js               — Svelte mount point