Idle Tuning: School of thought on ideal timing and RPM?
03-29-2014, 02:27 PM
#1
Safety Car
Thread Starter
Idle Tuning: School of thought on ideal timing and RPM?
I've never had an issue with my car idling poorly, but it's raining today and I figured I would mess around with it a bit and see if I could get a little more vacuum.
Quick specs: ls6, ls2 IM/tb, ysi, arun's stage 3 cam, e85
First thing I did was played around with the timing, I went as low as 19 degrees and as high as 28 degrees and it did not make much of a difference at all, 19 was a little too low but 21-26 lets say was exactly the same. So with this knowledge, what's the money spot to set it at so that the adaptive spark can still do it's thing?
Second thing I played around with is the idle RPM. A stock C5Z idles at 800 rpm. If I remember correctly (it's been a couple years) Greg Banish recommends adding ~50 rpm in Calibrated Success if you have a supercharger or a cam. However with my testing, I was able to pull the most vacuum at 900 rpm. So my question is should I leave it at 900 rpm? Are there pros/cons to that high of an RPM at idle?
*For those of you that don't know, the stage 3 cam specs are 230/242 .609/.615 115+3
Quick specs: ls6, ls2 IM/tb, ysi, arun's stage 3 cam, e85
First thing I did was played around with the timing, I went as low as 19 degrees and as high as 28 degrees and it did not make much of a difference at all, 19 was a little too low but 21-26 lets say was exactly the same. So with this knowledge, what's the money spot to set it at so that the adaptive spark can still do it's thing?
Second thing I played around with is the idle RPM. A stock C5Z idles at 800 rpm. If I remember correctly (it's been a couple years) Greg Banish recommends adding ~50 rpm in Calibrated Success if you have a supercharger or a cam. However with my testing, I was able to pull the most vacuum at 900 rpm. So my question is should I leave it at 900 rpm? Are there pros/cons to that high of an RPM at idle?
*For those of you that don't know, the stage 3 cam specs are 230/242 .609/.615 115+3
03-29-2014, 09:31 PM
#2
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St. Jude Donor '13-'14-'15
Idle tuning is really for drivability on the street--mainly for keeping it from dying when coming to a stop--and eliminating any surging or a hanging idle--So the advantage lies there---idle it where it seems to create NO issues driving around town--
Make sure you only make changes AFTER the car warms up and goes into "closed loop"
As when dead cold or even started warm for a few seconds the ECM is in open loop--where the idle tuning tables don't work well--- ( in OL the fuel is set by the open loop normal table-) so you can only adjust the idle timing----In closed loop you can adjust the fuel with the desired airflow table as there is NO IAC on a C5--and the desired idle table
More timing at idle is generally added on larger cams to aid in starting and for a smoother idle only
Make sure you only make changes AFTER the car warms up and goes into "closed loop"
As when dead cold or even started warm for a few seconds the ECM is in open loop--where the idle tuning tables don't work well--- ( in OL the fuel is set by the open loop normal table-) so you can only adjust the idle timing----In closed loop you can adjust the fuel with the desired airflow table as there is NO IAC on a C5--and the desired idle table
More timing at idle is generally added on larger cams to aid in starting and for a smoother idle only
04-01-2014, 09:21 AM
#4
230/242 is a pretty sizeable camshaft for a street driven car. I would expect plenty of change from stock with something that size, so going to a higher idle speed isn't out of the question if that's what it takes to keep it stable.
Getting maximum idle vacuum doesn't necessarily equal "better idle" either. You just want enough authority to avoid rolling idle speed, surging, or stalling as you change loads from gear engagement, A/C, power steering, or alternator loads. Make sure you have enough gap between your actual base idle timing and MBT so that there is a torque reserve available to make spark changes to control idle speed. If that works and the fueling is correct, chances are good that the car will drive well.
Getting maximum idle vacuum doesn't necessarily equal "better idle" either. You just want enough authority to avoid rolling idle speed, surging, or stalling as you change loads from gear engagement, A/C, power steering, or alternator loads. Make sure you have enough gap between your actual base idle timing and MBT so that there is a torque reserve available to make spark changes to control idle speed. If that works and the fueling is correct, chances are good that the car will drive well.
04-01-2014, 03:32 PM
#6
YES... as long as you are still satisfying the conditions needed for the ECM to recognize the difference between idle and cruising at 900-1000rpm. If these get confused, it can grab the hi/lo octane ("normal") spark table values and hang the RPM when it doesn't have a torque reserve with which to work at controlling idle RPM. That gap between the values *IS* the torque reserve for the most part.