Activities Hobbies Before Top-Dead-Center (BTDC) Print John H Glimmerveen. Licensed to About.com. Hobbies Cars & Motorcycles Motorcycles Cars Used Cars Trucks ATVs & Off Road Public Transportation Contests Couponing Freebies Frugal Living Fine Arts & Crafts Astrology Card Games & Gambling Playing Music Learn More By John Glimmerveen John Glimmerveen John Glimmerveen is a former competitive motorcycle racer. He later worked as a race technician for several international race teams. Learn about our Editorial Process Updated on 03/01/17 Definition: A common term used to indicate the amount of ignition advance. For instance, 10 degrees BTDC indicates the ignition timing is set 10 degrees before top-dead-center. Examples: Setting the ignition timing, so that the spark is initiated before top-dead-center, is necessary because of the time delay before the explosion reaches maximum force. The objective is to ensure the piston has begun its downward (power) stroke as the expanding gases reach their maximum pressure.