Stumped on scaled tune

[pknowles]

I have a 2001 Silverado 6L with a 78mm turbo system running a 2002 Tahoe flex fuel file with 2 bar applied. I've run this thing in OL, SD, and MAF tunes for the past few months with no issues at all. Everything works great. The truck just runs and drives better at low throttle and cruise with the MAF enabled. Unfortunately the stock MAF runs out of frequency around 6 psi of boost. So I installed an LS7 card style MAF, tuned the VE and MAF and everything was good.

I ran into the ECU limit of 4063lb/hr airflow around 9 psi of boost, so I see people scale their tunes (make the 6L think it's a 4L for instance) and scale everything proportionately. I scaled my tune by 2/3rds, OL and CLSD worked perfect. In fact, the VE table was extremely close and I didn't have to change anything, trims in CLSD look good. I did find that scaling the idle parameters were not good, so I left them as tuned before the scaling and everything runs and drives great (can't explain that). I used CLSD to tune the MAF, see MAF.jpg where black line is fitted MAF curve and magenta is Dynamic Airflow.
MAF.jpg

Then I enable the MAF and went for a drive on the scaled tune, only thing changed from CLSD is setting MAF fail freq back to 13000 from 0. Trims are good, but when I go full throttle, I get a huge lean spike. If you look at MAFscan.jpg you can see Dynamic Airflow at 1072 and Mass Airflow ~1300 are very different. So I tossed my CLSD tune back in. Look at CLSDscan.jpg, Dynamic Airflow is exactly where it should be around 1300 and AFR is good. Clearly for the MAF tune, AFR is following Dynamic Airflow and Dynamic airflow is way lower when enabling the MAF. MAF airflow is where it should be so it's not the MAF. One thing to note, I have my "High RPM Disable" set to 4000 RPM, so when it goes over 4k rpm it runs MAF only and AFR comes right in line. Before 4k is where I'm having trouble and I want to know why. Also, I don't have this problem on the non scaled tune.
CLSDscan.jpg MAFscan.jpg

What did I do wrong in scaling the tune for MAF? I'm a little stumped on this one and don't want to do a bunch of lean pulls to figure this out if someone sees the error. Thankfully I played it safe and have the boost turned way down for the first pull and have a tank full of E85. Thanks. Scaled.hpt

[pknowles]

Non Scaled tune attached.NonScaled.hpt

[pknowles]

On my scaled MAF tune, I plotted Dynamic Airflow vs my MAF curve, see below. Notice Dynamic Airflow (magenta) follows the MAF curve (black) until 6700 Hz then deviates then follows again at 8600 Hz. No doubt 8600 Hz is 4000 rpm where I'm MAF only (I checked). I enter PE at 6150 Hz, so I'm not sure what 6700 Hz corresponds to other than ~2900 RPM. Sorry for the multiple posts, but I'm struggling to figure out this behavior. Are the dynamic Airflow calculation equations posted anywhere for the different modes? Did I cross a boundary where Dynamic Air is calculated differently around 6700 Hz? I thought the calculation was VE based at low RPM, then blended in the middle, and MAF only at High RPM. Thanks.

scaled.hpl

[pknowles]

Well I looked through my later unscaled stock MAF logs, unscaled LS7 (card style) MAF logs, and then scaled LS7 (card style) MAF logs. I actually see this behavior in all of them. It always starts around 3,000 rpm, which is also my highest RPM zone boundary. I'm guessing the Dynamic Airflow calculation changes somehow above that boundary? If that's so, I'm thinking of moving the last RPM zone boundary above my rev limiter and also move the High RPM disable (MAF only RPM) down to cover this. Any information on how these calculations work is always appreciated.