There are basically 3 things you need to consider for timing - engine RPM, air / fuel ratio, and volume of air fuel mixture in the cylinder. (mechanics.stackexchange.com)
I'm learning about vacuum leaks on engine intakes and I'm hearing this terminology of lean air fuel mixture. (mechanics.stackexchange.com)
The intake ports create a swirl effect in the cylinder chamber that promote a well balanced and even air fuel mixture as it enters the engine. (autospeed.com)