# Dwell

In a gasoline engine , the dwell angle is the degree of rotation of the distributor shaft , while the primary circuit of the ignition coil is closed.

It depends on the number of cylinders in the engine and the type of ignition coil and can also be given as a percentage. In ignition systems with an ignition interrupter (contact breaker), the contact spacing determines the size of the dwell angle; the distance must be set to the value determined by the engine manufacturer and is usually 0.35 to 0.4 mm for four-cylinder engines .

If the contact distance and thus the dwell angle are set incorrectly, the ignition coil either does not achieve its rated output (contact distance too large = dwell angle too small) or is overheated (contact distance too small = dwell angle too large). Contactless ignition systems have no option for adjusting the dwell angle; there it is defined in the electronics.

The interrupter contact is actuated by the ignition cams on the distributor shaft, which runs at the camshaft speed (equal to half the crankshaft speed ). A 4-cylinder engine has four cams on the distributor shaft, which is why exactly 90 degrees of rotation are available for one cycle of loading and unloading.

A dwell angle of 45 ° (equal to 50%) to 50 ° (corresponds to 56%) is common here. The following applies: Closing angle = 90 ° - opening angle.

The information in percent refers to the angular degrees available for an ignition process (here 90 °) of the distributor shaft:
45 ° is 50 percent of 90 ° and 50 ° corresponds to about 56 percent of 90 °

## Six and eight cylinder engines

With a six-cylinder engine , one spark must be generated six times for each rotation of the distributor shaft: 60 angular degrees of rotation are available. The contact distance there is usually set to 0.25 mm with a correspondingly small dwell angle of approx. 38 ° and therefore a more powerful ignition coil must be used. Closing angle = 60 ° - opening angle.

Since only 45 ° of rotation of the distributor shaft is available in an eight-cylinder engine , it has an even smaller dwell angle of approx. 33 °. The closing angle is 45 ° - opening angle.

## literature

• Jürgen Kasedorf: Motor vehicle engine test. Petrol engines. 7th revised edition. Vogel Buchverlag, Würzburg 1997, ISBN 3-8023-0461-6 .
• Wilfried Staudt: Vehicle technology manual. Volume 2: Energy supply and starting systems, engine mechanics, engine management systems, exhaust systems. Bildungsverlag EINS, Troisdorf 2005, ISBN 3-427-04522-6 .