Riddle me this.

I dynoed a couple of weeks ago and got 285 whp. I checked my SAFC after the run and it showed a maf reading of 55%. I've always assumed that that particular number refers to the percent flowrate that the maf can handle, i.e., at 285 whp the engine was breathing in 55% of what the maf is capable of measuring.

I also know that the Z32 maf I am using is capable of measuring flowrate up to a quantity of air that would produce 520 hp at the flywheel.

So, 55% of 520 hp just happens to be 286 hp, almost exactly the number I got from the dyno.

BUT! For that to be true, then I should have gotten 285 hp at the flywheel, not at the wheels. For me to get 285 whp (which is about 340 at the flywheel), I should have seen a flowrate of 65%.

Any explanations for what is going on here?

 

I don't have an SAFC, so pardon my ignorance.

How does the SAFC know the maximum voltage the air flow meter can read?

Is it possible the meter does not operate at a linear rate?

Just throwing out ideas…

100% drivetrain efficiency

 

Good question. I'm not sure. When I had the A32 maf, I would see numbers up around 80%. 80% of 350 hp (what the A32 maf is good for) comes out to 280 hp, so that corresponds well with the 55% from the Z32 maf.

Very possible, especially if the Reynolds number gets high enough for transition to turbulent flow.

That would be nice, except that 285 hp at the engine is pretty low for 9-10 psi of boost.

 

The maf's voltage curve isn't linear.

 

That's probably the case. If you assume three points are enough to establish the relationship, it's not even that strongly nonlinear: