Ignition Timing and Engine Speed — Does timing advance with rpm? As engine speed rises in an SI engine, should ignition timing be advanced to maintain optimal combustion phasing?

Introduction / Context:
Ignition timing determines when the spark occurs relative to piston position. Because flame propagation time is roughly fixed in milliseconds, crankshaft degrees per millisecond increase with rpm, requiring timing changes to keep peak pressure properly phased after T.D.C.

Given Data / Assumptions:

• Spark-ignition engine with mechanical, vacuum, or electronic control.
• Normal operation without knock events forcing retard.

Concept / Approach:
At higher rpm, the piston moves faster and the time available per cycle shrinks. To maintain the target crank angle of peak pressure (often around 10–20 degrees ATDC), the spark must be issued earlier in crank degrees, i.e., more BTDC advance. Load, swirl/tumble, mixture, and EGR also influence the optimal advance, which modern ECUs manage via ignition maps and knock sensors.

Step-by-Step Solution:
Recognize finite flame speed: milliseconds do not change much with rpm.Convert time to crank angle: higher rpm → more degrees per ms.Advance timing with rpm to keep peak pressure after T.D.C.

Verification / Alternative check:
Timing curves (mechanical/vacuum advance) and ECU spark maps show increasing advance with rpm up to knock or MBT (minimum spark for best torque) limits.

Why Other Options Are Wrong:
“No” or limited-case answers ignore the fundamental time-to-angle relationship.

Common Pitfalls:
Assuming advance is monotonic at all loads; near WOT and high load, knock limits may reduce advance relative to part-load.

Final Answer:
Yes