Gas mileage and headers

[Bruce Plecan]

> 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.

Same thing happened when I did some mods...
With the better breathing at x amount of TPS, you're passing more air (hence
fuel), and probably a little better cylinder filling and less self EGR.

  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.

Need to rebalance timing fuel again.
Less EGR may need less timing, cause a dozen other things can come into
play.  Nother words burn a few more chips and see where your at.

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.

Too general of statement.
You have to optimise your tune when making changes like that.

> 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.)

Just the number of counts the IAC pintle is off of the seat.

> 6) Bumped base advance up to 10, was at 7.  No audible knock, no spark
> control counts.

Which when did you do that?.
If you make 2 changes atta time you have no clue which one did what.

> 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.

Starting 2-3 weeek Oct the Gas manufacturers start delivering Winter Fuel
Bruce


  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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