Re: LS1 Air Mass Meters

[Andrew Mattei <amattei@mindspring.com>]

> I've seen some of the performance shops here in Australia advertising
> "recalibrated Air Mass Meters" for the LS1, claiming HP gains of 25 or so.
> What on earth is "recalibrated!!", I thought the general mods to AMM's was
> opening them up a bit and that's it.
> Sound to me like if it is re-calibrating it must put incorrect values out to
> fool the PCM lean/rich, sounds like that Crane Box from years ago.
> By the way, at $800AUS they would want to work!!.

We've been beating on this old horse over on the LT1_Edit mailing list
as well (and also on the 4th Gen F-body list)... If you consider your
"standard" late model LT1/LS1 OEM MAF sensor as having the honeycomb air
straightening screen, as well as the large airfoil in the middle, and
the "aftermarket" units removing this screen and airfoil, there's a
pretty considerable amount of surface area that's opened up.

In the LT1 PCM (and this will be similar for the LS1), the calibration
curve table values are entered in Frequency, and they correspond to a
grams per second value. If you remove the above items from the MAF
sensor, you have thrown off its calibration, as its frequency will no
longer correspond to the "correct" g/s value. This has the effect of
making the car run leaner, and since the LT1 platform runs rich in the
first place, it shows a slight increase in horsepower... Think about it,
the MAF doesn't sense the whole amount of air going through it, so it
measures the air as less than it actually is, so the PCM calls for less
fuel than it really would have used before...

A couple of LT1_Edit users have redone their MAF calibration curves by
changing the value by about 5%-7% and are able to obtain proper (128)
integrator numbers. However, a number of people complain that with home
ported MAFs that they experience rough idling and intermittent other
strange behaviour.

Now, are these companies compensating for this with a "calibration"?
Making the frequency line up with the appropriate grams per second
values in the PCM table? That I do not know. There is a company selling
them here in the US as well - as a "calibrated" unit. Honestly, I have
my doubts. But who knows, maybe they do diddle with the electronics a
little bit. I've never even seen one of these aftermarket units in
person, though, I just know about the LT1/LS1 OEM units...

-Andrew
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