View Single Post
Old 01-17-2003, 06:56 PM   #41
Scooby Specialist
Member#: 14141
Join Date: Jan 2002
Location: [email protected] @ 5800 ft on 13T
2002 Impreza WRX

Default Great info


Great info.

So based on that then the short answer to my question above is the ECU attempts to get to a preprogrammed hard coded ideal advance for high octane fuel (or as close to that number as the algorthm will allow).
edit -- ( at least in any given cell of the table, so there is not a global fixed max timing, but a max in each cell)

This is an important non-trivial distinction vs the off set scenario for the following reason.

If this fixed advance max scenario is correct, then there is some octane of fuel that will give you the maximum possible ignition advance the ECU is allowed to give. In that case once you exceed that ideal octane level you will gain no more advance, and with the exceptions of a cushion of octane for changing conditions and possible differences in burn characteristics, going to a higher octane fuel will have no effect on advance and probably horse power.

If the off set scenario was the correct behavior of the ECU, then you could in effect tune the ignition timing the ECU would give you by finding the fuel octane that gave the mechanically ideal ignition advance.

Last -- although I think I know the answer just to be absolutely clear, are the algorthms you posted above, known to be true (at least in general behavior if not in exact construct) or are they hypothetical for the purposes of the discussion?

* Registered users of the site do not see these ads.

Last edited by hotrod; 01-17-2003 at 07:06 PM.
hotrod is offline   Reply With Quote