Foreword by Rinkrat456: This article is literally copied and pasted from Krambo's Silverado SS page. He is an HPTuners member on this site. I take ABSOLUTELY ZERO CREDIT for the length of material you're about to read, however I have made a few comments in-text that you can see which I will highlight in green. The pictures within this how-to are my contribution to aid in explaining what Krambo is trying to tell you. I have used this guide before with positive results and nothing jumps out at me as Krambo trying to pass on poor advice. I HIGHLY recommend reading through this entire guide before attempting to make changes to your engine. If any of the links stop working, PLEASE PM ME so I can fix them.
The following is a collection of idle tuning notes, tips ‘n tricks and How-2’s for idle tuning a big cam (or any cam for that matter) that I used when dialing in my 248/254, .615"/.622", 112 LSA using HP Tuners. If you choose to follow any of these How-2’s, please do so at your own risk and do one change at a time…in other words, I am not responsible if you blow it up or damage your engine. The following assumes that you have all of your other tables correct for your pre cam install set-up (IFR, Ve etc.). He means this too...don't skip straight to fine tuning your idle if you're unsure of your injector data or you know ahead of time that your VE table is garbage. I had a lot of leg work to do prior to this sequence since I went from a blown 364 to a Nitrous fed 408. O.K. If you are not familiar with the tables in HPT, this may be very confusing. To those that have the software and can follow, PLEASE ADD YOUR EXPERIENCES, so this thread can be utilized for all the do-it-yourself tuners. <<<I took his advice and now this is what you're reading.
Alright, you have your new cam installed, degreed and ready to fire. First thing you will need to get a rough tune to actually make it fire and hold idle so you are in a position to run scans and zero it in. As a GERNERAL guideline, you can follow this suggestion:
Cams with negative overlap up to zero, set idle to 850-900 all cells across the board, add 1 g/sec to idle airflow across the board both in P/N and in gear (HPT > Engine > Idle > Idle Airflow > Base Running Airflow), add 2º of idle timing 1200 rpm and under and 0.08 – 0.28 g/cyl inclusive (HPT > Engine > Spark Control > Spark Advance > Idle Spark Advance (in Park).
Cams with over 0º overlap up to 15º, idle 900-950 all cells across the board, add 2 g/sec to idle airflow across the board both in P/N and in gear (HPT > Engine > Idle > Idle Airflow > Base Running Airflow), add 4º of idle timing 1200 rpm and under and 0.08 – 0.28 g/cyl inclusive (HPT > Engine > Spark Control > Spark Advance > Idle Spark Advance (in Park).
Cams over 15º overlap, idle 950-1100 all cells across the board, add 3-4 g/sec to idle airflow across the board both in P/N and in gear (HPT > Engine > Idle > Idle Airflow > Base Running Airflow), add 6º of idle timing 1200 rpm and under and 0.08 – 0.28 g/cyl inclusive (HPT > Engine > Spark Control > Spark Advance > Idle Spark Advance (in Park).
You can go to this link --> Overlap Calculator to determine your cam overlap. Have your cam card handy and follow the inputs in the calculator. My cam has a very healthy 27* of positive overlap which is on the very high end of any cam you will typically find on a street driven truck.
Confused already?...are your units as you want them to be? Are you stuck in lb/min or g/sec? Right click on the cells, scroll down to "UNITS" and select the way you want your data presented to you.
Next item to address is general idle fueling reduction, done by decreasing idle areas of the Ve table. Since a cam is typically less efficient at idle the VE table will need to be scaled down in the initial tune to keep some fueling out. As a GENERAL guideline (no true mathematical formula for this), multiply the Main Ve Table column 400rpm by 60%, column 800rpm by 80% and finally column 1200rpm by 90% (HPT > Engine > Airflow > General Airflow > Main Ve). Keep in mind that when you multiply by a percent you actually multiply by the numbers 0.6, 0.8 and 0.9 respectively. Do NOT multiply by 60, 80 and 90! Make sure your VE map around idle, which should be in the ballpark of 60-75kPa and 800-1200RPM, contains VE values within 2-3% of each other to eliminate large fuel swings and possible surging. Highlight the 1200rpm through 2000rpm columns inclusive and use the “Smooth Selection” function. This will give a nice curve and should avoid surging due to fueling. In my opinion, take this part of the guide as a wake-up call to expect that less fuel will be needed with a big cam down low. If cutting down to 60%, 80% and 90% prevents the engine from starting because it doesn't have enough fuel now, add fuel back. On smaller cams you don't have to cut as much fuel as big cams. Small cams may be able to simply start right up using the factory VE cells around idle. Take note if your operating system uses a primary and a secondary VE table in case you find yourself in Speed Density mode, which then your secondary VE table is referenced. Whatever changes you make to the primary VE table will have to be manipulated in the secondary VE as well.
Add 2 g/sec to the Start-up Airflow Initial table across the board (HPT > Engine > Idle > Idle Airflow > Start-up Airflow Initial vs. ECT). <<You'll want to revisit this table once you have your base running airflow dialed in fairly well to avoid start-up flairs. Look at an LS6's table for reference.
Add 50 camshaft rotations to the Idle Start-up Airflow Delay vs. ECT (HPT > Engine > Idle > Idle Airflow > Start-up Airflow Delay).
Make sure that your Idle Spark Advance table (both “In Drive” and “In Park”) match your High and Low Octane Table for all columns up to 1200rpm (HPT > Engine > Spark Control > Spark Advance > Idle Spark Advance (in Park, in Gear), Hi and Lo Octane). Blend the timing numbers into the 1600rpm+ columns so there are no huge numerical transitions. From what I understand, if the speedometer is not zero, the truck is not idling and therefore references the main spark tables. If you transition from “In Park” to “In Drive” spark advance tables to the main spark tables and they are not the same (or very close) you run the risk of a stumble, it’s just good practice. You'll have to come back to these tables once you find exactly where your cam likes to idle for spark...there's a part in this guide explaining how to find the "strongest" map value using the spark advance in the bi-directional controls of the VCM scanner. Once you figure that value out you can come back to these 3 or 4 tables. See picture
I'll also add that I believe most of us can benefit from commanding stoich after the engine comes up in temperature and continues to reach operating temp. To do this during the idle tuning process, go to Engine > Fuel Control > OL&CL >Open Loop EQ Ratio and set columns 140-230*F to = 1 which will command the PCM to set fueling to ~14.7. Smooth the transitions by selecting the neighboring columns if you wish. You'll have to force the PCM to stay in open loop as well, which means setting the Closed Loop Enable ECT vs IAT table to Max value (284*F)
With all of the changes done above, the truck should fire and hold idle. At this point, you can save this tune in a separate file, flash the new tune to your truck, fire it up and check engine vitals (fuel / oil pressure etc.) and get a heat cycle into your new valve springs (assuming you swapped them) OR you can dive strait into logging for the Desired Base Running Airflow numbers based on your specific cam and engine set-up.
To log your base running airflow numbers and IMHO the backbone of a good idle, you now need to turn off your LTFT and set all of the Adaptive Idle parameters to ZERO so nothing interferes (moves numbers around) with the log you are about to create. To do this go to HPT > Engine > Fuel Control > OL&CL > Long Term Fuel Trim Enable, and make both the Min. and Max. ECT settings equal to 284*F <<or on some vehicles just use the drop down menu to disable. Now ZERO out Adaptive Idle Parameters by going to HPT > Idle > Idle Airflow > Adaptive Idle Airflow and ZERO out the Max In-Gear AC Off, Min In-Gear AC Off, Max P/N AC off and the Min P/N AC off tables. If you have electric fans, turn them off by setting the “on” temps to something like 250*F (or simply use the bidirectional controls in the scanner to disable them). Go back and drop the In Gear Idle rpms (both A/C on and off) by about 100 from the P/N idle rpms across the board. Save this tune file with a file name you can remember (i.e. Idle Airflow Tuning) and flash the PCM with these new changes.