Re: AFM->MAF: chip vs. split-sec

[Rob Clark <rclark@xxxxxxxxxx>]

Neil Deshpande:
> I had put out a similar mail some time ago and was replied to by Jim =
> Conforti himself.
>
> Reprogramming the ECU is most certainly the most elegant way to go.  It =
> has been done for the E36 (M3 only, maybe) and you can see Duane Collie's =
> comments on the system's performance on Turner Motorsports' WWW page.

I found that article, but I couldn't tell from it whether the car
originally had an AFM, or if it was just replacing the original MAF
with a bigger one?  Anyone know?

> Reprogramming the ECU takes tons of dyno time.  There are apparently no =
> equations that can give you the engine curves, etc., and one has to =
> determine them by experiment.  Of course, a custom chip can be written for =
> any engine mod (this one included), but it would not be cost effective to =
> do it for the E30 since enough E30 owners would not be interested.  I =
> guess the $850 that Split Second charges is lower than what Jim C., for =
> example, would charge to develop a custom chip.

Yeah, I didn't mean to make it sound easy.

What I was hypothesizing is that you could take an existing fuel
curve, and remove two of the axis:  temp and pressure.

I thought that what the cpu really wants to know when it computes
how much fuel to inject is the mass of the air, which is the signal
that a MAF gives you, but the original part was a AFM, so the cpu
has to correct for temp and pressure.  (ideal gas law omitted)  All
that you need to do to make the MAF work is undo (or remove) the
correction that the cpu makes.  Right?

Of course this is a little far fetched, but hey, I am still in the
hypothesizing stage.  This would require (1) that two of the axis
of the fuel curve are indeed pressure and temp, which is something
that I can only assume, and (2) an existing fuel curve to start
from.  I guess if one knew the format of the data stored in the
EPROM, that it might be possible to get the existing curve.  (The
EPROM that the e30s used wasn't any esoteric non-off-the-shelf chip
was it?)

- ---
Rob Clark  (Rob_Clark@domain.elided)
San Diego
BMWCCA
87 325is 

------------------------------