converting target AFR's for different scalings
 

Hey Guys,

If I have a target AFR or 12.0 in a ROM with injector scaling of 542 and I want to convert it to a ROM with injector scaling of 513 can I just do:

new target = old target * 513/542?

ie 12.0 in 542 = 11.36 in 513?

or is it the other way around

ie 12.0 in 542 is 12.68 in 513?

Cheers
Dave

it SHOULD go small.
that should read, 12 to 12.68.

!!!!!! i'm gonna have to disagree.

i think your misunderstanding the question.

yes if you put in smaller injectors the AFR is going to increase. (run leaner)

but he wants to go from a map scaled at 542 to 513. so using a smaller scale - you will have to target a richer afr to get the same afr as with the 542 scale. assuming no injectors are being changed - only the afr targets.



uh.... ok now im totally confused.

i think your right - AFR mapped with 513cc/min will run richer than the same target with a 542 scaling. some people scale injectors smaller to run richer. so yeah - nothere should be right. the whole map needs to be leaned out if you rescale to 513.


and why is tephra asking this question? you're the expert! LOL.

hmm. if 542 = global lean and 513 = global rich then 542/513* 12.0=12.68

or does it even change at all?

remembering the AFR is a ratio, so the ECU uses the AFR to work out how much fuel to inject based on the airflow, then works out how long to keep the injector open based on scaling.

does that make sense?

if you change injectors _and_ the scaling, final AFR does not change. of you keep the same injectors and AFR map, changing the scale will affect final AFR.

if you change the scale _and_) injectors to 513 from 542, duty cycle would have to increase to hit the target AFR in your map. but if you don't actually change the injector - the same injector will just add more fuel. hence why some people scale the injector smaller as a global richen.

So as you decrease your scaling the ECU thinks it needs to open the injectors for longer to hit the same target AFR

HOWEVER - You haven't changed the injectors - so you are now opening the same injectors for longer which means you are getting more fuel - hence a lower/richer AFR.

So to compensate you should lean out your fuel maps - thus making the AFR numbers bigger.

Does that make sense?

yes thats exactly what i was getting at.

EDIT :: Please don't listen to any of this ... keep reading. =)

If you are going by your example when you are trying to use a map tuned for larger injectors on smaller injectors ...

The map values will be too LEAN for the smaller injectors, so you will need to LOWER the values in the map to get the same AFR. Remember, the map essentially assigns a pulse width based on RPM and MAF reading, so the lower map value would give the smaller injectors a longer pulse width, which is what you want.

So, 12.0 in 542 = 11.36 in 513, or ...

old map target * (new inj size / tuned inj size) = New map target

I don't think the ECU actually reads the AFR map as a ratio ... the values in the map are simply scaled and displayed to read more like a ratio. The values are not technically AFR targets or even AFR values at all. If you've tuned other ECU's such as UTEC you'll get what I mean.

Geez .. it feels weird to disagree with you ... :confused:

That's correct, Dave.


Eric

I guess my confusion is that the injectors aren't actually being changed ...

Decreasing the scaling will increase the amount of fuel injected. In order to keep the tune the same with the scaling decreased, you will have to decrease the amount of fuel injected in another table. Using the AFR target table, you increase the number to decrease the fuel, and because that is what you want to do the AFR target will increase.

So in order to keep the tune the same without changing anything physical (i.e. injectors):

if injector scaling goes down: Fuel table goes up

if injector scaling goes up: Fuel table goes down.

-Paul

I got it now ... I was thinking backward.

My thought process was around changing injectors and leaving the scaling, which would be the exact opposite.

ok sounds good - thanks all!

just coz i'm good with the code doesn't mean my brain automatically grasps simple concepts :P ahahah