Gas mileage and headers

[Programmer]

Seems with a MAF equipped vehicle, as you increase flow--mileage goes down.
Ever throw a new air filter in when the old one was plugged and notice your
mileage goes to crap again ? You'll definitely have to reprogram to make it
work... just my .040 cents CDN <g>.
Lyndon
-----Original Message-----
From: Marteney, Steven J. <smarteney at xlvision.com>
To: gmecm at diy-efi.org <gmecm at diy-efi.org>
Date: October 25, 2000 1:27 PM
Subject: Gas mileage and headers


>Well, the addition of 1 3/4" SLP headers to my 89 Formula 355 (165 ECM,
>MAF), ZZ3 cam, flat-top 10.2:1 piston ride has dropped my hiway mileage a
>tad.  I haven't formally checked it yet but today I would usually have 1/4
>tank showing on the gauge for my ride home from work (40 miles) and I only
>have less than an 1/8.  Mileage at last fill-up was 17.3mpg, but that had
>some in town driving in it so I discounted it.  Now with the gauge on empty
>when it's normally not, I'm puzzled.  Will be checking mileage in about 2
>hours when I leave work but wanted to get this email out for review asap.
>Mileage had not varied at all prior to the headers.  Well, it varied, but I
>was always able to make it home at this point in the week.  So, I guess my
>BROAD question is how can headers adversely effect gas mileage?  I would
>think it would be the same or better.
>
>I've been scanning with Diacom on rides to and from work and the results
for
>75mph, 2300rpm with cruise on are:
>1) BLM actually DOWN maybe 1 count to 121-122, was 128 before the headers.
>2) BLI about 125-127 and varies +/- 8.
>2) Pulse width the same as before, about 3.1-3.2msec
>3) TPS voltage the same or less at 1.04V (was typically 1.04V to 1.08V)
>4) MAF reading about the same
>5) Idel Air Position at 129, up from previous 120 (still don't know how to
>read that.)
>6) Bumped base advance up to 10, was at 7.  No audible knock, no spark
>control counts.
>6) A/C now off, whereas before it was on
>
>The last one I think is the biggest clue, while the car was laid up for 2
>weeks whilst I put the headers on (don't ask) the weather changed here.
>(Central Florida, from 85-90 during the day to high 70's.)  I've never
>driven this car in anything but high heat and humidity, but I thought that
>would hinder mileage more than this 50% humidity I'm experiencing now.
>Also, the engine temps are way down.  It usually ran on the hiway at about
>190F and now is around 179F.  Performance is WAY up after the headers.
>Butt-o-meter is pegged and one of those home dyno thingies shows 30 ft-lbs
>more torque and 10 more peak hp.
>
>I'm just wondering if I'm merely fighting slight weather change or if the
>headers have screwed with the tune.  I noticed the oxygen sensor (which was
>new 6 months ago) gets located further down the pipeline.  Although, I
can't
>understand why the all the variables are staying the same above but mileage
>decreases.  Do I need to go back to 7deg base advance?  (BTW - no trouble
>codes either.)
>
>Thanks for letting me think out loud.  Sorry for the length.  Any insight
is
>GREATLY, GREATLY appreciated.  Still learning...
>
>Steve
>PS - In addition to the headers, I added a Random Tech converter.  Nice
>unit, great sound.  :-)  Very happy, just paying a little more money for
gas
>than I think I have to.
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