Idle Tuning (spark igntion timing )

[Gelf VXR]

I started a new thread although I have posted in another as this is not really related to EGT&CHT tuning.

https://forum.efilive.com/showthread...nd-EGT-and-CHT


So I had set about seeing the effects on EGT by advancing idle spark, however I became more interested in how far I was able to advance timing, conventional wisdom on forums say advance timing until to lowest MAP is observed, retard back a few degrees to allow for idle spark corrections.


I was able to advance timing from 10* to 50* and observe MAP decreasing from average 50kPa to 41kPa, plotting a trend line suggested MAP would level out at 55*.

Fuel consumption at stock 13* is calculated at around 3 litres per hour, reducing to around 2.1 litres at 50*. Air flow reduced proportionally from around 9g/sec to 6g/sec.


I've never seen anyone suggest such high idle timing, in another article which kind of prompted me to do this analysis http://www.carprogrammer.com/Z28/PCM...k%20tuning.htm MAP was observed to drop to 45kPa and rise again at around 34* timing, I have a similar cam 216/229 with .610" lift in an LS2 with LS3 heads.

Has anyone else increased and logged their idle timing, what were the results?

[joecar]

I saw that in your charts, but the MAP chart did not click in my head until now (that you mentioned it)...

What is the slowest idle rpm that your cam likes...?

[wyochimneysweep]

what are you seeing for egt's at idle? Mines at 800f right now

[Gelf VXR]

I saw that in your charts, but the MAP chart did not click in my head until now (that you mentioned it)...

What is the slowest idle rpm that your cam likes...?

When I was calibrating the MAF and VE using 40* idle timing, it would idle around 750 fairly consistent with idle spark correction tables zero'd.

[Gelf VXR]

Interestingly, and I forgot about this table in the LS1, B5919 optimal timing "This table is used as a reference for what would be best timing, which is then used for various torque calculations"

Which would indicate 50* at 0.08gcyl @ 800rpm and 38* at 0.16gcyl @ 800rpm

[joecar]

Interesting... so that (lowest MAP) is the basis of B5919.

[Gelf VXR]

I think there's a correlation, optimum timing should yield the lowest MAP, for later PCM's I can not locate B5919, I'm sure the table must be in there somewhere as torque calculations are still made. Noted that as bore and ci increase, required timing follows suit.

I understand retarded timings purpose is to keep EGT high and cats hot to meet emissions, id rather save a 1/3 of fuel at idle. I 'd question the logic of burning 1/3 more fuel to meet emissions? CO reduction vs CO produced from the extra fuel?

[Gelf VXR]

There is a way to find the GM optimal timing value, just need to additionally log the E40.TORQUECALC.DMA, TRQENG_C

[ringram]

The only consideration I can see for not going too close to lowest MAP is for idle control with AC, power steering load, alternator load etc. If you are too close to MBT and LBT at idle you have no room to take on load.

I log the torque pids and you can make a very accurate looking bhp and torque run with them. So they should tell you about best spark for MBT for sure. Once you get MBT then vary fueling in open loop to get LBT as well.
But as above, this is not what I would do as you then have zero room to vary spark for engine load. You are limited to throttle action which is slow and cumbersome and likely to cause erratic idle.

That being said you are likely to have the lowest airflow at LBT and MBT. Therefore lowest fuel consumption

[Gelf VXR]

The only consideration I can see for not going too close to lowest MAP is for idle control with AC, power steering load, alternator load etc. If you are too close to MBT and LBT at idle you have no room to take on load.

I log the torque pids and you can make a very accurate looking bhp and torque run with them. So they should tell you about best spark for MBT for sure. Once you get MBT then vary fueling in open loop to get LBT as well.
But as above, this is not what I would do as you then have zero room to vary spark for engine load. You are limited to throttle action which is slow and cumbersome and likely to cause erratic idle.

That being said you are likely to have the lowest airflow at LBT and MBT. Therefore lowest fuel consumption

I just looked at the AC engage /disengage in the calibration, it allows for 20NM, I need to plot the calculated torque to find out how much timing that would require and reduce back from MBT, bummer if its 13* lol