E40 SD Tune Airflow Limit?

[FSAE_Junkie]

I have an 05 GTO with a 402 and F1A procharger with 2.5bar OS that I have been running on a restrictor for the past two years because I've been avoiding wanting to deal with a scaled tune (and the nearly $2k expense for some ID 1300's).

Well, I finally bit the bullet and picked up a flex fuel sensor, and some ID1300's and am trying to find the best strategy for tune scaling. I don't need all of the injector at 58 psi, so I'm going to run it at 43 psi and I think this will put me nearly exactly at 2x the 63.5 lb/hr injector limit. I think this gives me 2 options.

1) Do the full scaling of every every airflow related table

2) Double Stoich, Halve the Injector Flow Rate, and halve the IVT AFR table

Number 2 seems like the obvious choice, but I've read quite a few comments about an airflow limit even in SD that you can run into with just the stoic scaling. Sure enough when, I got back and look at my logs, my VE airflow caps out at 67.72 lb/min. But coincidentally, this occurs right at about peak power just before redline, so I've never actually seen if this limits fueling or not.

I guess I'm curious if anyone knows if this is just a limit on the airflow it can report, or if this actually holds back fuel?

[FSAE_Junkie]

Hmm, so it took looking through about a hundred threads, but I may have finally found the answer:

https://forum.hptuners.com/showthrea...r-boosted-TBSS

This was in reference to max airflow on an E40:
"Yes though some of the reporting still maxes out at some point. Mine won't show over 512 g/sec VE airflow but fueling continues to stay steady so it's working fine. Just some kind of reporting limit."

I think at this point then, I may just try the Stoich scaling for the new injectors and see what happens. Then, since I'm near the max value as it is, when I take the restrictor out, I can see if the engine goes lean at airflow's above 67 lb/min. I'll just have to be sort of easy with it and not do a full redline pull on the first try just in case it does start capping fueling.

Any other reasons why stoich scaling is not a good idea on an SD tuned E40?

[Lakegoat]

If you are 2 bar SD, the boost VE table runs out to 255kpa. How much boost are you running? The spark table maxes at 1.36 gs, but follows the last row as you pass 1.36.

[Alvin]

The half injector double stoich is the simplest easiest way.

When I initially read this I thought you were running into a VE airflow limit problem and I was going to suggest looking at [ECM] 13425

The scanner will have limits on airflow reporting but the ECM still climb.

[FSAE_Junkie]

Yea but with an E40 speed density tune that doesn't matter. Still not sure I get it though; So I have 100 #'ers, if I was starting off with a stock tune with 33# injectors I would just triple stoich and thats it?

The E40 still hits an airflow limit in SD. At least the blown TBSS I worked on did. No matter what, it would lean out until I scaled it.

Took me a while to find the thread again, but this comment above is what got me going down the path of thinking that the simple method wouldn't work due to the the 67 lb/min limit even in SD.

If you are 2 bar SD, the boost VE table runs out to 255kpa. How much boost are you running? The spark table maxes at 1.36 gs, but follows the last row as you pass 1.36.

Yeah, I?m not near the 255 kPa limit, I?m only running about 9 psi now with the restrictor and hoping for 15-18 without. I?m already getting close to the spark table max, so if I double stoich and don?t scale airflow, I should be well beyond the spark table airflow. But, I?m not sure this is an issue yet, because even now, when I get into boost, I sort of level out spark. At the end of the day, without a decent chunk of time on a dyno, it?s hard to tune spark (and trade that against risk of being too aggressive).

The half injector double stoich is the simplest easiest way.
When I initially read this I thought you were running into a VE airflow limit problem and I was going to suggest looking at [ECM] 13425
The scanner will have limits on airflow reporting but the ECM still climb.

This is what I was hoping to hear. That it was more of a reporting limit rather than a fueling limit.

[FSAE_Junkie]

I thought I would update how this went. The few weeks it was going to take me to get up and running turned into several months, but I finally got the new injectors installed. I did prove to myself that the 67 lb/hr airflow limit is only a reporting limit and doesn't seem to affect fueling in my 2.5 bar SD tune. I'm not sure what issue DSteck was running into.

To get the ID1300X2's to work, I went the stoich scaling route with the lower fuel pressure to keep the injector flow rate low enough to allow stoich scaling, since the stoich table limits you to about 2.3x. I'm surprised how easy this was, I had been dreading moving to bigger injectors for years because of how terrible this car ran when I bought it with a scaled airflow tune.

Interestingly, I see tons of mentions to making sure you halve the IVT terms when you double stoich. Well, I did that, and my first start (which was fine prior to this) now took 8 seconds of cranking with no other changes. Hot restarts were fine, but starts after 4+ hours of sitting consistently took between 5-8 seconds. I increased the IVT terms back from 50% to 75% of the stock value and now cold starts are fine. I haven't tried going back to 100% the stock value to see if it's any better or worse, but it seems fine with where it's at.

I think in the long term, I'm going to have to do a 50% airflow scale along with the 50% stoich scale so that I can make full use of the injectors at 58 psi fuel pressure or higher.