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Old 01-02-2005, 12:06 PM   #1
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Member#: 20161
Join Date: Jun 2002
Chapter/Region: International
Location: Florida, Ankara
1998 Impreza ST

Default Ignition Timing and AFR's

Hi all

I know ecu mapping is not a DIY job and it is dangerous for who is not sure what is he doing but I'm just trying to learn with very cautious plays.
I have been examining the ignition and fuel maps in my ECU and have also tracing the map and have just been learning the parts of the map my car uses, logging egt and afr readings in various driving conditions.

Now, working out how much fuel to remove or add from the fuel map for it.What effect does ignition timing have on power, is this even more potent way of extracting performance. How much of an adjustment to say advance or retard of the timing would be considered a good starting point ?, Has anyone got any actual data on the effects of increasing ignition advance by X number of degrees and/or of richening leaning off of a map on power ?

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Old 01-02-2005, 03:23 PM   #2
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Join Date: Mar 2004
Chapter/Region: NWIC
Location: Seattle, WA
04 Improved STI
Dirty White


Read jblaine's thread "Let's talk about AFRs..."

Read a few books on tuning. I really like the Jeff Hartman book "How to Tune and Modify Engine Management Systems".

In a nutshell timing determines when the combustion (fuel burning a set rate in the chamber) is applying the most pressure to the piston after top dead center (TDC). Timing affects power, but the power is in the fuel and air combo, not the spark. The goal is to spark combustion such that you impart the maximum possible torque to the crankshaft. Timing changes with RPM and more significantly with the octane of the fuel (higher octane fuel burns more slowly in general). Finding the spark advance point of maximun brake torque (MBT) is one of the main difficulties of tuning. Mostly it is determined by experience coupled with trial and error. Monitoring air-to-fuel ratios and exhaust gas temperature will get you only so far, eventually you need actual power readings and that means strapping your car to a chassis dynometer.
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Old 01-02-2005, 04:02 PM   #3
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Here is the link for the Let's talk AFRs thread. It's long but full of very good tuning information, including the data you are looking for.

Ecutek also has a good article on explaining Subaru's Active Ignition Timing.
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