Gas mileage and headers

[Bruce Plecan]

> Well, I don't understand that either, but I've heard it said "the IAC is
> basically a vacuum leak."

An ecm controlled one.

>  That should mean the MAF wouldn't see it, right?

It's down stream of the MAF in all the applications I know off, so it is
accounted for, the only variable for air not seen that changes much is the
PCV.  Even the brake booster doesn't change it much (g/sec readings)

> I'm working on some data and have some interesting results from driving
> tests yesterday.  I've got to go back to the archives and check some my
> thoughts and equations before I post to the list.  (Yes, that's right,
I've
> been parsing through the archives.  Circle the calendar!)

We'll be asking trick guestions then LOL
Bruce
   GN is almost docile enough to let Doc drive around in now.  Other guys
just are a little too eager to get the keys yet......
   trouble now is heard Doc talking to someone about a passport to Yemen, he
wants to lead an unofficial investigation, and then fire up some Tomahawks.
He's definietly from the old school..

>
> More later,
> Steve
>
> -----Original Message-----
> From: Bob Valentine [mailto:bob at tecmark.com]
> Sent: Thursday, October 26, 2000 5:16 PM
> To: gmecm at diy-efi.org
> Subject: RE: Gas mileage and headers
>
>
> Hmmm....  higher IAC counts = more air past throttle blades.
>
> Still can't understand why that wouldn't show up in the MAF reading, but
> then I've never done any MAF tuning.
>
> -> Bob
>
>
> At 11:50 AM 10/26/2000 -0400, you wrote:
> >That's the thing that's driving me crazy!!!  I would expect more pedal
> input
> >to show up as more TPS voltage (at the same rpm and gearing) or as higher
> >MAF reading or more fuel shown as a higher BLM.  But it doesn't.  The
block
> >learn multipler is lower, the reported pulsewidth is the same, the MAF
> >reading is the same.  (Of course, by "same" I mean there is some high
> >frequency variation between Diacom frames but they are generally
averaging
> >about the same.)  Back a couple of months ago when I was doing minor chip
> >tuning for the highway I was bumping up the timing in individual cells
and
> >could see the BLM, MAF reading, and pulsewidth go down for the same rpm
and
> >cruise speed.  Now, the only Diacom parameter that changed is IAC counts
> >went up 10, and coolant and intake air temps went down 5 to 10degF.  I
> >mentioned the timing change previously.  Maybe that's it.  Seems
> >counter-intuitive to me, but I'm probably just thinking too hard.  I'll
> keep
> >working on it.
> >
> >Thanks again for tolerating the out-loud thinking!
> >Steve
> >
> >>As far as the mpg going down after header install, it could be the oxy
> >>fuel, or it just could be the fact that you torque curve has been
shifted.
> >>Depending on the design of the header, you can lose bottom end torque,
and
> >>with OD at highway speeds, your operating in that range.  Less torque
> >>requires more pedal input and more gas.
> --------------------------------------------------------------------------
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