could anyone explain to me how auto advance systems work, both vacuum and mechanical.

Adam

could anyone explain to me how auto advance systems work, both vacuum and mechanical.

Adam

I'm no expert but auto-advance is there to make the ignition system work at the same speed as the engine. If you want to know more there are plenty of manuals around that explains the system better than most people can. Try a manual relating to a really old car coz the diagram's tend to be easier to follow ( & read with eyesight like mine).

mechanical works by bob weights spinning outwards with centrifugal force and pushing the rear points plate around to advance the ignition as the motor increases with speed.

vaccuum works the same way but uses the intake manifold to move the plate, as when the engine speed increases it draws more vacuum thus moving the plate more.

when i say points they could also be conactless using hall effect or magnetic triggers.

on fully electronic systems the advance is "mapped" into the rev range to provide differing curves for each gear and revs.

thanks for the replies, but i am more interested in why there is a need for auto advance? as in what are it advantages etc

Adam

The answer is in the replies. It's there to allow the engine to accellerate. If there wasn't auto-advance the engine wouldn't go faster than idle (well not with out a fight & other problems).

thanks for the replies, but i am more interested in why there is a need for auto advance? as in what are it advantages etc

Adam

Given that it takes a certain amount of time to fully burn the fuel / air mixture, the point of ignition has to vary in proportion to engine speed

Make some assumptions here just for a guide

At tickover speed of 1200 rpm,the ignition advavce is set to 2mm before TDC

so assume that all the fuel is burned at TDC

But at 8000rpm there will be much less time for the piston to travel from 2mm BTDC to TDC

there would not in fact be enough time to burn all the fuel

To overcome this, the point of ignition has to be advanced as the revs rise, and this is the reason for advance retard systems

Hope this helps

Given that it takes a certain amount of time to fully burn the fuel / air mixture, the point of ignition has to vary in proportion to engine speed

Make some assumptions here just for a guide

At tickover speed of 1200 rpm,the ignition advavce is set to 2mm before TDC

so assume that all the fuel is burned at TDC

But at 8000rpm there will be much less time for the piston to travel from 2mm BTDC to TDC

there would not in fact be enough time to burn all the fuel

To overcome this, the point of ignition has to be advanced as the revs rise, and this is the reason for advance retard systems

Hope this helps

i agree, its called the flame front. as the fuel is ignitied and piston speed increases, the ignition has to start early to complete combustion.

In the early days you had to retard the ignition (ie piston after TDC) just to get the buggers going (engine efficiencies/compression/shit fuel/etc)

thanks guys i get it now

Adam

thanks guys i get it now

Adam

and here was me thinkin 'auto advance' was something your boss gave you on a friday afternoon!!!!!!!