Gas mileage and headers

[Marteney, Steven J.]

Well, I don't understand that either, but I've heard it said "the IAC is
basically a vacuum leak."  That should mean the MAF wouldn't see it, right?

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!)

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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