Engine displacement: total volume swept by all cylinders during one engine cycle. Calculation: displacement = (π × bore²/4) × stroke × number of cylinders. BORE = cylinder diameter; STROKE = piston travel distance from top dead center to bottom dead center. Units: LITERS (L) (1L = 1000 cc) — modern standard; CUBIC CENTIMETERS (cc) — same as liters but for small engines (motorcycles); CUBIC INCHES (CID) — older US system. Conversions: 1L ≈ 61 CID. Examples: 2.0L = 2000 cc ≈ 122 CID; 5.0L V8 ≈ 305 CID; 350 CID ≈ 5.7L. Larger displacement engines typically (but not always) produce more power, use more fuel, and weigh more. Modern trends: TURBOCHARGED smaller engines produce power similar to older larger engines with better fuel economy (a 2.0L turbo can match a 3.5L naturally aspirated). PISTON CYCLE in terms of displacement: piston travels from TOP DEAD CENTER (TDC) to BOTTOM DEAD CENTER (BDC) and back; full displacement is swept twice per complete four-stroke cycle (each stroke is half the displacement). NATURAL ASPIRATION vs FORCED INDUCTION: (1) NA engines breathe air at atmospheric pressure; (2) TURBOCHARGED engines use exhaust-driven turbine to spin compressor that forces more air in — more air = more fuel = more power; (3) SUPERCHARGED engines use belt-driven compressor for same effect; more responsive but consumes engine power. Boost pressures typically 6-20+ psi above atmospheric.
Engine output: HORSEPOWER (HP) — rate of work output; usually peaks at higher RPM; TORQUE (lb-ft or Nm) — rotational force; typically peaks at lower-mid RPM. HP = (Torque × RPM) / 5252; both curves cross at 5252 RPM on a dyno graph. Modern car engines: 100-200 HP typical for small cars; 250-400 HP common; performance/luxury 400-700+; supercars 700-1500+ HP. RPM ranges: idle 600-900; cruising 1500-3000; redline 5000-8000 (gasoline), 3000-5000 (diesel).
Compression ratio: ratio of cylinder volume at BDC to volume at TDC; higher compression = more efficient, more power, requires higher-octane fuel; gasoline 8:1 to 12:1 typical (high-performance up to 14:1); diesel 14:1 to 22:1 (uses compression for ignition).
Octane rating: gasoline's resistance to KNOCK/PRE-IGNITION; higher octane (87, 89, 91, 93 in US) tolerates higher compression and timing advance; use what manufacturer specifies; using higher than required doesn't improve performance; using lower than required can damage engine.
Knock: premature ignition causing pressure waves; can damage pistons; detected by knock sensors which retard timing.