https://help.estesrockets.com/hc/en-us/articles/8445801084301-What-do-the-engine-codes-mean

Each engine has a letter number-number code (e.g., B6-4).

The letter indicates total impulse. This is the total power (in Newton seconds) produced by the engine. Each succeeding letter has up to twice the total power as the previous letter. For example, a ‘B’ engine has twice the power of an ‘A’ engine; a 'C' is twice as powerful as a 'B'; etc..

The first number in the code refers to the average thrust of the engine. Average thrust is the engine’s average push, or how fast the engine powers the rocket to go. The higher the number, the faster the speed. Higher average thrust engines may be the best choice for heavier models or models with higher drag factors such as a larger diameter.

The final number in the code gives you the timed delay in seconds between the end of the thrust phase and the ignition of the ejection charge. Selecting the correct delay allows your rocket to reach apogee which in most instances is the best time for the recovery system to be deployed. Engine codes ending in ‘0’ have no timed delay and are used for booster stages and special purposes only. Engines ending in ‘P’ have no timed delay or ejection charge and the forward end is “Plugged” so that no hot gases are released from the forward end.