Using advance and retard for power and economy

[obi_waynne]

What effect does advance and retarding the ignition on a car have on

1) Performance
2) Economy

Is there a general rule of thumb here on how far to tweak it?

Today with all these ECU's chips and computer things it is easy to lose track of the real basics of car tuning.

 

[HDi fun]

The rule is to advance as far as possible until pre-ignition or knocking sets in under all operating conditions. There are no exceptions to this.

 

[obi_waynne]

Does this maximise both power and economy then?

I would approach it by finding the pinking limit and then backing off a bit - is that sensible?

Also you set the timing by rotating the distributer? Have you ever known the breakers or advance mechanism to need tweaking?

 

[HDi fun]

If you're adjusting an older car then you must set the timing according to the makers spec. This can be static or dynamic.

The distributor mechanism will provide compensation for revs (using mechanical centrifugal advance) and for load (using vacuum retard).

The basic goal is the same. As far advanced as possible for economy and power. Modern systems achieve perfect timing. Mechanical system don't - there's no 'closed loop' in the form of a knock sensor.

One problem with using maximum advance is that it can increase HC content in the exhaust. But it also lowers CO.