What is vital for a smoothly operating engine?

Equal compression between cylinders is essential for a smoothly operating engine because it ensures that each cylinder is producing power efficiently and uniformly. In an internal combustion engine, each cylinder must compress the air-fuel mixture to the same pressure for optimal combustion. If one or more cylinders have lower compression due to wear, damage, or issues like leaking valves or piston rings, the engine will experience rough running, misfires, and a noticeable loss of power. This uniformity helps maintain balance and smoothness in engine performance, contributing to both power delivery and engine longevity.

Higher oil pressure is important for engine lubrication, cold temperatures can affect engine performance but are not inherently vital in all operating conditions, and while clear exhaust emissions are beneficial for environmental reasons, they do not directly relate to the engine's operation and performance in terms of power generation and efficiency.