Questions after updating fuel injector data

[JimMueller]

Summary:
After updating the FIC data to what Calibrated Success measured, I'm having worse fuel economy and my MAF g/s has gone up as much as 70g/s at WOT. Did I do something wrong?

Detail:
I originally requested a recommended injector here:
https://forum.hptuners.com/showthrea...ecommendations

I ordered this part based upon that thread:
https://fuelinjectorconnection.com/c...lb-ls2-l92-lq4

On May 28 020, FIC provided the attached file named "FIC440CC-42LBBOSCHLS1SCALEDHPT".

On October 12-14 2021, Greg & FIC began announcing the availability of fully characterized data:
https://www.corvetteforum.com/forums...aboration.html

On October 13 2021, Bob at FIC sent me the updated data, attached filename "440ccHPT_Plug_and_Play_Data_FIC_42lbLS1(6660) "

After applying the updates to the calibration, I noted that the new data didn't discuss what to use for the minimum & default injector pulse, nor for the short pulse limit. My old values were not OEM and I do not recall from where I obtained the data or recommendation to change them. Bob said to put them back to OEM. Greg said he leaves the short pulse limit at the factory 4.0 value and no need to change. Greg only recommends "lowering the min default injector pulse if you find that you are actually riding that limit during hot idle or cruise. Lowering it shouldn't hurt, though. Just keep in mind that some injectors get inconsistent at very short pulse widths and this value is intended to keep you away from that."

My concerns here are:
1) The large increase in MAF g/s has significantly reduced how much overhead I have remaining below the 512g/s MAF limit.
2) The reduced fuel economy in the same OLMAF mode
3) My MAF logs regularly show lean between roughly idle and 3500Hz after multiple adjustments, it seems as if its never satisfied. The data above that Hz has stabilized, albeit at higher airflow rates.

The "Oct21" tune is with the new data, the "03Oct" tune is with the old data. What do I log to determine whether I am "riding that limit" during hot idle or cruise? Other suggestions?

[eficalibrator]

If you previously tuned the car with a different injector data set, then whatever errors may have been present in that data got "baked in" to your resulting AFR/Lambda error calculations and airflow models. Changing only the injector model (even if it's to 100% correct data) still means that you'd need to offset these changes in your airflow models. Yes, even if it "ran ok" before, that was only likely because of a stackup of opposing errors that got undone by correcting the fuel injector data to something more accurate.

You SHOULD expect to need to go back and redo the MAF (and speed density) airflow model after correcting the injector data. The good news is that if you do this correctly, you will find that the car runs much better (with small fuel trims) even as weather and driving conditions change.

1) In other words, your issue #1 is probably real now because the new MAF calculation is based on accurate fuel flow data and AFR. ASSuming you have what I know know as "FIC_660_42lbLS1" injectors (which seems to match your second excel file), their flow rate is actually about 7.4g/s (almost 59#/hr) at 400kPa, which is closing in on the factory 8.00g/s Injector Flow Rate limit. Not surprisingly, GM also put the airflow limit of 512g/s at a point where these two often converge up top. (Your car is probably moving good air and making good power)

2) If you were running at lambda=1.0 before and after, there should be no change in fuel economy from fixing injector and airflow models. Worse fuel economy makes me think you were either lean before or are running rich now, particularly on tip-in events. Again, you need to fix BOTH the MAF and SD airflow model. If you find that lowering the airflow does not yield a reduction in logged PW at the same RPM/MAP or MAF Hz, then you should see if your base PW (final PW minus voltage offset) is riding the limit mentioned above. After all this is done, you can confirm that you have the appropriate spark advance.

3) Did I mention you should tune BOTH airflow models? Even a "maf only" tune doesn't completely ignore the SD model when the system is not stable. All of these steps are clearly demonstrated in our training videos shown in my sig.

[JimMueller]

Hi Greg,

I did expect to re-tune but I didn't expect the deltas to be so large. I do tune both MAF & VE and did buy your 1st DVD. I just happened to start retuning with MAF to get an idea how far off the injector changes would be before I spent excessive time on the VE tables. I'm going to check for new vacuum and exhaust leaks so I'm not chasing my tail.

Once I know there are no leaks, I'll recheck the MAF & VE. This is just a 12:1 418 LS3 with a smallish cam (232/242 114+4) and unported, milled LS3 heads with a valve job. I had really hoped there would be more MAF headroom to grow within this PCM without scaling, and I have no desire to change PCMs. Of course I could disable the MAF.

Ideally I want about 550-600rwhp max (all N/A, peaking 6000-6500, max RPM 7000) in the future, and I think to ensure I had the 20% safety margin I estimated 650bhp, .45 BSFC, that gave me 46lb@58PSI injectors, and I was told these FICs would be 50lb@58PSI, not almost 60lb@58PSI. So it appears I could be better served with accurate injector data that peaks near 46lb@58PSI or 6g/s? If I can lower it from 7.4g/s to ~6g/s, it may give me some of the extra MAF headroom I desire? Have you tested any injectors that are near that criteria?

[eficalibrator]

Once I know there are no leaks, I'll recheck the MAF & VE. This is just a 12:1 418 LS3 with a smallish cam (232/242 114+4)

Not a "Smallish" cam where I come from, but I usually have to pass emissions.

Ideally I want about 550-600rwhp max (all N/A, peaking 6000-6500, max RPM 7000) in the future, and I think to ensure I had the 20% safety margin I estimated 650bhp, .45 BSFC, that gave me 46lb@58PSI injectors, and I was told these FICs would be 50lb@58PSI, not almost 60lb@58PSI. So it appears I could be better served with accurate injector data that peaks near 46lb@58PSI or 6g/s? If I can lower it from 7.4g/s to ~6g/s, it may give me some of the extra MAF headroom I desire? Have you tested any injectors that are near that criteria?

Your original data for these injectors was wrong. Sorry, but I had nothing to do with it there. The new data showing 59#/hr at 4 bar is correct.

So, this means that when you were working with the lower IFR, you had effectively been working with a scaled tune. Now you are working at face value, with better precision but larger numbers. As long as you don't end up hitting the 512g/s limit, you'll be fine. Ignoring the MAF and only using speed density just runs into a similar issue around 1.2g/cyl, which is pretty much in the same zone. (This is why my scaling method makes you change BOTH air and fuel and not just IFR/stoich since you'd hit the air per cylinder limit in SD and have the same problem all over again!)

If the injectors you have on the car allow for decent fuel control at small pulsewidths (hot idle, cruising at light load) on the bottom end and don't exceed 90% DC near redline, they're probably just fine for your application and I wouldn't recommend spending more money on something else. If you're not hitting the Hz or g/s MAF limits, you're fine there too. Getting to within 3% of the 512g/s limit in cool air is just fine.

If it were me, I'd be excited that I now have an accurate airflow number for my engine that likely correlates with measured power on the dyno. It was likely pretty far off before and this explains it. Just finish dialing it in with the current hardware (and good data) and enjoy the car.