DFORESI

Hi everyone,

General:
I have finally gotten my supercharged LS3 Corvette project running and ready for tuning, exciting stuff. The car has Novi 1500 blower and ID1000 injectors. I have a base calibration that I made using the ID injector data. In this calibration I increased the start up airflow (car starts really well) and I've also been adding to the "Airflow Final Minimum" table to give the engine extra torque to spin the blower. Due to my E38 injector hard limit, I scaled the injector flow to 50% and doubled the stoich table to compensate.

Problem:
The car doesn't idle smoothly, I'm pretty sure the injectors are not at fault as I started the car with the factory injectors and the behavior was the same. When the car was bone stock it would idle with the MAF reading about 7.7g/s of air flow, now with the supercharger installed I see anywhere from 8 - 8.5g/s of airflow at idle. The issue is that the idle lopes and I see huge swings in spark advance in order to keep the engine alive. To me this would indicate the engine needs more air, but when I modify the Airflow Final Minimum table it doesn't seem to effect the actual airflow.
@650rpm in Neutral factory cal was 6.40g/s
Now @650 in Neutral my calibration is 9.54g/s
I'm still seeing only 8 - 8.5g/s at idle. I have been increasing the airflow in 10% increments from stock to the point where I'm at now, which is 49% over stock, with no changes in idle performance.

Is it possible that I'm missing some table or that I'm pushing up against some limit? Throttle position actually seems to back off the more airflow I add:

stock +10% = 7.7deg
stock +21% = 7.3deg
stock +40% = 6.9deg

Mass airflow also seems to follow the same pattern ^^


Current cal and idle log attached.
Thank you for your support.

ChopperDoc

I may be wrong, but I'm pretty sure idle air is controlled more by VE than the MAF, meaning calculated dynamic air which comes from VE at lower RPM's. What you can try here is simply tuning your VE table in the idle areas, as this will affect your idle air tables. If the calculations on the VE are off, which they appear to be, then then engine will keep adding fuel. Also note that MAF is very inaccurate at idle and low rpm, and normally comes into 100% use above 4k rpm. Take a look at your dynamic airflow under the airflow tab to see what I'm talking about.

Also, I'm not super up to date on the newer PCM's, but you only have a 1 bar VE table, however the new MAF hard limit is 4000 g/s, which is more than enough, so.....

Looking at your tune, I didn't see a boost enrichment table either, so I must ask, are you planning to run a 2 bar OS? Might be worth considering in order to get the right numbers on the VE table. Up to you though, but I would at least research it. Like I said, not sure if you can get away with a MAF only on this set up. I would contact support@hptuners.com and see what they can do for you as far as application and OS goes, and other possible options. They can at least add the boost enrichment table for you lol.

I know it's built into the editor now to change it yourself, but all that stuff is new to me lol. I'm still like 20 years behind the times lol.

The last car I did I simply disabled the VE table by reducing the enable RPM to 100 for dynamic air, forcing it to use MAF. This was a cammed 2014 Camaro SS though, no supercharger. After that a MAF tune got everything working fine, and it ran great. I simply told him, if your MAF ever fails, you have to fix that right away. He is well aware of it and I made that clear. I added 15% fuel to his VE table anyway just in case but didn't tune it since I only had a few hours to get it done.

Not sure if that's the proper route for boost though, but the option is there.

DFORESI

ChopperDoc, thanks for the detailed reply, this is awesome! I'm not new to tuning but this is my first GM vehicle, I was able to get most of this figured out, but just in case someone searches this in the future, I should provide some closure.

First of all, yes you are correct. At idle the MAF is not really used because it is very inconsistent and the flow in the intake can be very turbulent. Referencing the VE table is a far more effective way of controlling idle and this is what the PCM does. I eventually put the vehicle into speed density only and the idle problems vanished. Then I collected closed loop data at idle and applied the fuel trims to the VE table, now the idle is on point.

On newer PCMs the VE table limit is pretty high as far as I can tell. It is a Virtual VE table which is calculated using coefficients, so if you run off the map it will still keep calculating based on the pre-defined polynomials. I have since updated the VVE table to reflect higher areas of pressure. I'm still waiting on my LS9 MAP sensor to get in before I can actually make my way into that area of the VE table. In essence, no you do not need a custom OS because you can just modify the axis and then recalculate the VE coefficients.

The route you described regarding lowering dynamic airflow to enable MAF only operation is still valid on GEN 4. I am currently running a MAF only tune and have been able to get the car to run very well right into full boost. Once I get the new MAP sensor and can tune the VE table I will revert the changes to dynamic airflow and allow the system to run as usual.

Thank you very much for taking the time to look into this. Hopefully this helps someone in the future.

ChopperDoc

I'm glad you got it ironed out. Yeah the MAF usually messes with idle real bad with heavy mods, particularly big cams. That's pretty good to know that you can keep the VE a 1 bar and redefine it. Honestly I think just going to 2 or 3 bar is a lot easier lol. I am really glad they build the virtual VE into the editor now though. I still have the bluecat tool for editing that thing.

And you can change the OS in the editor now (not sure when they changed this lol). Played around with it, definitely pretty cool. It made my VE max out though, so copying some things over is required, but it's that simple.