a MAF too small (!)

[Daniel Ciobota]

> Heres a new one: How about if, when I change the injectors I just
> make the new MAF bypass tube exactly the same ratio change as the
> injectors ratio change? I mean stock injectors were 22#, new
> injectors are 28#  so I add inlet area to the MAF that is 28/22
> larger than the original!  NO ECM CHANGES!  did I hit on something
> here? at idle the car would see  less airflow than stock , and
> provide a reduced inj pulse.. which is correct cause the injectors
> are exactly proportionally sized larger.  huh.

Dave, you have just hit upon the way mustang mafs get recalibrated... pretty much
the same way, they just use a smaller diameter sample tube, area inverse
proportional to the change in injector rate.  It's a good place to start, then you
can tweak it later for more exact flow ratios (the bypass tube doesn't flow quite
as efficiently as the straight-through maf).

Btw, I think the ford mafs can be quite easily adapted for use in place of
frequency output units;  as I understand, they're a current bridge design, so it's
fairly easy to hook up a voltage controlled oscillator to simulate a frequency
type maf sensor.  Bruce et al. could probably do this in their sleep!  :-)  If you
can do that, a whole new world of mafs is open for you, with units flowing up to
1500cfm (yep, not a misprint!) and with a miriad of injector calibrations already
available.   Plus, you can find them used for real cheap (like $150 or so, with
sensor).  Yes, it will make your engine a mutt, but hey, why not use the best of
all options, right?  For a low budget racer like myself, I don't mind a bit
putting a gm single wire alternator in a ford (done it twice), or buick 2 bar maps
for my boost spark control.  Whatever works, I say.

Also, depending on the mods to your motor, a 5psi blower on a 5.7l chevy should
run somewhere between 300 (bone stock motor) to 400 (al heads, mild cam, freely
breathing intake and exh).  At 400 you're right at the 750 cfm limit, so I'm
starting to wonder if your sensor truly flows 750cfm... what diameter housing is
it? It should be at least 70mm for that kind of flow.  I own an 89 vette (165
ARAR), and the modified sensor housing I have (72mm) flows only 720 or so cfm,
according to TPIS.  You might want to double check the flow.

Daniel