Double Stoich and Halve IFR Injector Scaling how to

[MStefak]

Just figured this out now figured Id make a new thread that will be easily searchable.

To scale your injectors with the double stoich and halve your ifr method do the following.

- Take the Flow rate vs pressure data for your NEW INJECTORS and multiply by .5 effectively cutting them in halve.
- Take your desired AFR and multiple by 2 , effectively doubling its value.

- Next you MUST take your Open Loop Fueling tables into account. ** I have now learned that the tables become to lean , not too rich. Start increasing the tables for engine temps below say 20c and all IVT temps -40 to max by 10% until the after start stumble of stall has disapated. The reason for this is that the IVTs become falsely warm due to the skewed AFR numbers and lean thr mixture far to quickly.

- Next is cranking fuel. I have practically doubled mine from 60c and below and about 1.5 60c to 100c ( fic 1000s 105 lb/hr @ 4bar) and it starts faster then the day I bought it off the lot.

This really only seems to be necessary for us poor saps that freeze half the year and mod their daily driver . All you warm weather guys probably wont ever hit these temps ..

As I figure out how to return the IVTs back to normal ill update this thread.

[LT1Z]

Don't forget the effect on transient fueling.

[MStefak]

That's why I need to return the IVT back to a " normal " value .. just have no idea how to go about that yet

[alexl226]

Don't forget the effect on transient fueling.

Please share!!

[alexl226]

Next you MUST take your Open Loop Fueling tables and cut the cold fueling in half. What I did was take the entire -40c row and multiplied by .5 , then I interpolated between that row and the next row that was smaller than it.

This really only seems to be necessary for us poor saps that freeze half the year and mod their daily driver . All you warm weather guys probably wont ever hit these temps ..

Hmmm. This one is new to me. If you started with the lowest table (-40) what temp did you interpolate to??

Also you said table"s" so I'm assuming both the alcohol and gas should be changed?

[MStefak]

Alex, I have changed my first post. The next day I figured out I was wrong. The mixture is actually far to lean. I think it is even from gm.

[MStefak]

And i interpolated -40 to 30c

[Niemer]

I've been fighting these issues all winter. Mine goes lean on coastdown and has an off idle stumble until it warms up, then all is well. I've taken care of a lot of the problem by playing with idle spark, but it's still not perfect. There is a definite correlation between the severity of the stumble and the outside temp.

[MStefak]

Is it a closed loop or open loop issue ?

Transient fueling will do that log you etc , IVT , and find out how cold it's gotta be.

More attention to the IVT. Goto you transient fueling tables and find that cell. As far as I can't tell you can affect transient by modifying one of the two tables. Either make the pcm think more or less fuel will evaporate ( by modifying the evaporated table) or make it think more or less fuel will make it into the chamber ( modify the other , can't remember it's name off hand )

[eficalibrator]

Guys, please keep in mind that this scaling method still has some limitations. It does not address either the 512g/s total airflow limit or the 1.28g/cyl limit present in many GM ECMs.

Chances are that if you are legitimately making enough power to need injectors bigger than 8.0g/s flow rate, then you probably also have an engine capable of flowing more than 512g/s (about 650hp, give or take). If you run into this limit, the ECM will still drift lean at the top end unless you opt for the more involved method of scaling fuel flow, ALL air flow/mass values (g, g/s, g/cyl), and torques. This method has been discussed on here previously by myself and James (RWTD). There is also a great demo included in my Advanced GM Tuning DVD (Summit part# SME-DVD-2) where I show the before/after results of scaling side by side on a split screen.

[MStefak]

To note , the e38 platform can use the hptuners enhancement to remove this limitation. It allows a modifiable g/cylinder making that a nine issue ( besides loosing resolution when going too high ) and a much higher maf limit as well

[DSteck]

Guys, please keep in mind that this scaling method still has some limitations. It does not address either the 512g/s total airflow limit or the 1.28g/cyl limit present in many GM ECMs.

Chances are that if you are legitimately making enough power to need injectors bigger than 8.0g/s flow rate, then you probably also have an engine capable of flowing more than 512g/s (about 650hp, give or take). If you run into this limit, the ECM will still drift lean at the top end unless you opt for the more involved method of scaling fuel flow, ALL air flow/mass values (g, g/s, g/cyl), and torques. This method has been discussed on here previously by myself and James (RWTD). There is also a great demo included in my Advanced GM Tuning DVD (Summit part# SME-DVD-2) where I show the before/after results of scaling side by side on a split screen.

To be fair, I do this quote often and never have a problem. Unlimited licensing lets me use the custom OS to alleviate the airflow limit (or I just tune in speed density), and there are tricks to get more timing adjustment after 1.36g/cyl. My own car runs like this (and I have to so that my 4L80 doesn't fall apart from grossly low torque reporting).

There's drawbacks to both methods. It is easier for the average Joe to do the stoich trick. If there was a good methodical way to adjust the torque reporting besides a wild ass guess, I'd scale my car the long way.