So I have been running 2.36" exhaust since I boosted my car and had the car perfectly tuned 11.2-11.6 in boost (running 10.5:1 c/r so its a leniant a/f) and it was running rich in vacuum mainly because I was too lazy to tune out vacuum

So yesterday I built a new exhaust system went with a 3" straight pipe with no muffler, resonator or anything........yes its loud, but I will be soon getting a apexi muffler on there. BUT in the mean time, the car is running REALLY lean, I cant get the boost to get richer then 12.5:1 under boost......does a VERY free flowing exhaust effect a/f that much, and what would you guys suggest to do to get more fuel in there??

BTW here is a pic of my exhaust...under axle:D

 

your engine isn't trying as hard to move air through it now so it's moving more air and the map is reading the same pressures it's used to so it's dumping in the same amount of fuel.

that much fuel + more air = leaner mix

 

either tune it out or turn up the fuel pressure a bit.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 01geeser &raquo;</TD></TR><TR><TD CLASS="quote">either tune it out or turn up the fuel pressure a bit.</TD></TR></TABLE>

OHH, thanks....I have been trying to tune it out, but hasnt been effecting it, I am going to bump the fuel pressure and see how she runs...thanks!

 

Widebands read richer at higher pressures because the density is greater. You're probably running a bit leaner from being more efficient, and reading a bit leaner from having less backpressure. Combo of the two.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">Another effect is that higher pressures contain more oxygen and fuel molecules and thus require a larger pump current to come to equilibrium. This gives the indication the mixture is richer than it would be if measured at normal atmospheric pressure. This effect is particularly important for turbo engines where poor sensor placement can fool you into thinking you have a richer mixture than you really have. </TD></TR></TABLE>

TechEdge info sheet, near the bottom

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nicklk &raquo;</TD></TR><TR><TD CLASS="quote">

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damn........thats one stright-thru exhaust! must be loud as fok!

 

So the past few nights I have been playing with the tune and not getting anywhere....

Increased fuel pressure to 47 over 45psi....nothing

Increased the boost fuel table 15% nothing...another 10%....nothing...whatcha guys think?

 

Dude, you have a straight pipe!