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Originally Posted by NoDOHC
Ignition Timing (BTDC) Manifold Pressure at Idle (kPA relative) Idle AFR
20 -75 to -80 12.2-12.7 *These are very close
15 -70 to -75 12.5-13.0 *These are also very close
10 -65 to -70 12.8-13.2 *More of an estimate on the AFR, vacuum is right
5 -60 to -65 13.0-13.5 *Pretty accurate (ran for a while at this)
0 -55 to -60 13.4-13.8 *Ran for a few minutes only
-5 -50 to -55 13.7-14.4 *Ran for weeks
-10 -45 to -50 14.4-15.0 *Was running at 14.8, closed loop until my fuel system gave up the ghost from the E85.
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Please allow me to correct some misinformation here. These numbers were taken using my old AEM wideband.
A new, calibrated Haltech wideband is now indicating that my AFRs were not stoic as I originally thought.
The table above should actually read more like this:
Ignition Timing (BTDC) Manifold Pressure at Idle (kPA relative) Idle AFR
20 -70 to -75 12.4-12.6
15 -66 to -70 12.6-12.9
10 -62 to -66 12.9-13.1
5 -58 to -62 13.1-13.2
0 -53 to -58 13.2-13.3
-5 -49 to -53 13.4-13.6
-10 -45 to -49 13.8-14.0
I tried retarding the timing more, but the AFR had to actually go richer again as I went in that direction.
This is all taken at 700 RPM (my new idle). I was idling at about 1,000 rpm before, but I got tired of waiting for the trans to stop to use reverse.
Advancing the timing past 20 degrees didn't really increase the manifold vacuum any, nor did I see any changes in the AFR (went from 20 to 40 degrees with no noticeable change.
The engine will idle at stoic, but it misfired every 2 seconds or so (very annoying).
I apologize for the misinformation, it was correct to the best of my knowledge.
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Originally Posted by TitaniumTT
porting plays a HUGE role in that as well
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Correct you are!
I should list my porting - stock port timing (open/close), slightly cleaned up.