Engine Performance & Tuning Flashcards

What is the primary function of a catalytic converter?

Answer: To chemically convert harmful exhaust pollutants (HC, CO, NOx) into less harmful substances

A three-way catalytic converter uses precious metal catalysts (platinum, palladium, rhodium) to oxidize hydrocarbons and CO while reducing NOx into nitrogen, CO2, and water.

A 'cat-back' exhaust system replaces components:

Answer: From the catalytic converter outlet back to the tailpipe

Cat-back systems replace everything after the catalytic converter — mid-pipe, resonator, muffler, and tip — improving exhaust flow and sound while retaining the emissions-legal cat.

Excessive exhaust backpressure in a performance engine will typically:

Answer: Reduce power by inhibiting efficient expulsion of burned gases from cylinders

High backpressure forces the piston to work against exhaust resistance during the exhaust stroke and can cause exhaust gases to re-enter the cylinder, diluting the fresh charge and reducing power.

Variable Valve Timing (VVT) systems are designed to:

Answer: Adjust camshaft phasing to optimize valve timing across different RPM ranges

VVT systems (e.g., Honda VTEC, Toyota VVT-i) advance or retard camshaft timing relative to the crankshaft, optimizing the valve events for low-RPM torque and high-RPM power.

Direct injection (DI) differs from port injection primarily because DI:

Answer: Injects fuel directly into the combustion chamber at high pressure

Direct injection sprays fuel directly into the cylinder under very high pressure (100–350 bar), enabling better fuel atomization, precise control, and charge cooling that allows higher compression ratios.

A cold air intake (CAI) improves engine performance primarily by:

Answer: Drawing cooler, denser air from outside the hot engine bay, increasing oxygen content per charge

Cooler ambient air is denser and contains more oxygen molecules per unit volume than hot underhood air, allowing more fuel to be burned per cycle and producing more power.

ECU remapping (also called a 'tune' or 'flash') modifies:

Answer: The lookup tables and parameters stored in the engine control unit that govern fueling, timing, and boost

Remapping overwrites the ECU's factory calibration maps (fuel, ignition timing, boost targets, rev limits) with optimized values suited to the engine's actual hardware and fuel quality.