Gas mileage and headers

[Len Sabatine]

   Re Fomuluated Gasoline contains [ MTBE] Oxygen Bearing Compounds,
   which will trigger the O2 # to ADD FUEL, which is indicated by your ST
   Fuel Trim hovering in the low 120s. The ECM is Subtracting Fuel to 
compensate.
  The headers also have increased  scavenging , which will increase total 
air flow thru the engine.
   The O2 placement is most likely farther down stream than the factory 
position, which
   tends to slow down it's response. All of these changes point to re 
optimizing
  your Fueling , Spark and EGR response settings. RFG usually reduces fuel
  mileage 2 MPG on many vehicles. Interesting how RFG is supposed to help
  improve  air quality , while consuming MORE FUEL. Another Govt brain
storm gone astray it appears, RFG will be phased out within 3 years from a
recent fed law change. When the MTBE is removed in the spring , operating 
conditions
will change again , tune to the best compromise with pump gas.
Len
>Well, that is very interesting.  I installed the headers with less than a
>1/4 tank.  Ran that out and filled up.  Ran the car for 1.5 days (work
>trips) and took a sick day.  Ran it for 1 day after that, which was a
>Friday, and I was left with a little less than 1/4 of a tank for the
>weekend.  That lasted me til Sunday.  Sunday afternoon I decided to the bump
>the timing to 10, from 8.  Sunday night I filled up and checked the mileage.
>It was 17.3.  3 days later, with more highway miles in this tank, I fill up
>again and it's 16.7.  (The norm had been 18.0)
>
>I re-checked the timing this morning and it had slipped to 8 deg.  Don't
>know how or why, distributor was still tight.  Set it again to 10.  I'll run
>this tank through and check again.
>
>I've got a question on the EGR aspect.  If truly this combo now has less
>self EGR and therefore uses a bit more fuel, can I compensate for this by
>porting the EGR?  What I mean is, these aftermarket EGR valves always come
>with multiple sized washers and you pick the one from a table corresponding
>to your car.  Can I install a larger inner diameter washer between the EGR
>and intake manifold?  Just a thought, what do you think?  Is it worth a try.
>
>Thanks all,
>Steve
>
>-----Original Message-----
>From: Bruce Plecan [mailto:nacelp at bright.net]
>Sent: Wednesday, October 25, 2000 7:30 PM
>To: gmecm at diy-efi.org
>Subject: Re: Gas mileage and headers
>
>
> > 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.
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