EFI University

FPSeth · Joined: 03 May 2010 Posts: 25 Location: Right next to YUL

I never understood this, but I'm sure somebody more intelligent than me can explain it:
Lets use an example of an oem MAF based engine- Nissan, Subaru or Ford:

Lets say i start with a 2.0 liter subaru, and the MAF scaling (I like Ford's term: MAF transfer function) is tuned perfectly for the given fuel system+injectors.

Now, I pull that motor out, add displacement to make it a 2.5 liter, add larger lift and longer duration cams and improve the flow capabilities of the cylinder heads.
I re-install said motor with the exact same fuel system, injectors, MAF and piping before and after the MAF.

Now, in my head, i have installed a much more efficient airpump, but the measuring system of the air is identical so I should just be running at a higher voltage of the MAF curve, right? Increase the crank fuel and I should be able to start it up drive away. But the reality and my experience has always been that the car will run very lean and the actual shape of the MAF curve will change, sometimes subtly and sometimes dramatically.

WHY?

Tomak

StantonWarrior · Joined: 10 Dec 2010 Posts: 188 Location: UK

It really depends on the ecu in question.
I think also the assumption is the linearisation of the output will still be scaled correctly for a higher airflow and usually isn't the case.

For ecus where true speed density is used ie MAP and maf is pretty much a fail safe reference, you can. Eg Bosch MExx
Especially so when torque model hasn't been played with.