Engine fundamentals — firing order of a horizontally opposed (boxer) four-cylinder engine Select the commonly used firing order for an opposed four-cylinder internal combustion engine used in automotive applications.

Introduction / Context:
Firing order is the sequence in which cylinders deliver power strokes. It affects engine balance, vibration, crankshaft design, and exhaust pulsing. Boxer four engines (horizontally opposed) typically use a firing order optimized for smoothness and even exhaust intervals.

Given Data / Assumptions:

• Four-cylinder boxer layout with 180° opposed banks.
• Crankpins arranged to achieve even firing intervals over 720° of crank rotation.
• Automotive spark-ignition application.

Concept / Approach:
For a four-cylinder engine, power strokes occur every 180° of crank rotation. In the boxer layout, the firing order 1-4-3-2 yields good balance and exhaust separation. While inline-4 engines often use 1-3-4-2, boxer-4s commonly adopt 1-4-3-2 in many classic designs.

Step-by-Step Solution:

Verification / Alternative check:
Service manuals for well-known boxer engines list 1-4-3-2 as the firing order, confirming the common choice.

Why Other Options Are Wrong:

• 1-2-3-4 and 4-3-2-1: lead to uneven balance and undesirable pulsation.
• 1-3-4-2: more typical of inline-4 engines.
• 1-3-2-4: not standard for most boxer-4 automotive applications.

Common Pitfalls:
Confusing cylinder numbering conventions between manufacturers; assuming inline and boxer engines share the same firing order.

Final Answer: