Timing For Modified Engines First Fives（时间修改引擎第一个5）.PDF

Ignition Timing for Modified Engines An often neglected but important area when tuning an engine is the ignition system. No I dont mean harder plugs, competition coils, lumenition etc., that only affect the efficiency of the spark, but the actual ignition advance supplied by the distributor. Tuned and modified engines have different advance characteristics and requirements from a normal engine. Adapting the advance curve to meet these requirements using the standard mechanical distributor is not that difficult a task once it is understood. This area is often considered to be a black art, but it is actually quite straightforward. Correctly setting the advance curve for a modified engine can make a considerable difference to the tractability of the engine as well as ensuring that the engine is giving of its best power wise. Modifying the advance in the way described can only be done on an engine that uses mechanical advance. Some engines use mapped ignition which is electronically controlled, Ford ESC, EECIV, Bosch K,L Jetronic, Motronic are examples. These are not suitable for modification. A quick and easy check to see if your distributor has an advance mechanism is to remove the distributor cap, grasp the rotor arm firmly and try to turn it in a clockwise direction. If it allows 10 or so degrees of movement and then springs back, then it contains a centrifugal advance mechanism and is suitable for modification, if it is rock solid, dont mess with it, its mapped. Why an engine needs more advance as its speed increases When the compressed mixture inside a cylinder is ignited it takes time for the flame front to reach the piston and for the expanding gases to start pushing it down. The time that this takes changes according to a number of variables such as mixture strength, how well the cylin