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I have dyno'd with and without cats without this huge difference of which you speak.  Narrow band is not an exact science I agree but the voltage on my car still reads about the same.
If it's true that we are here to help others, then what exactly are the others here for?
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Wow, good info guys, thanks.
Looks like I was way off :rolleyes:
Marco Tatta
98.5 SE MTX, Duratec
EGR block, fog light
fix, custom shift boot, monsterflow intake, Ecotek valve
Quasi dual cardoctor exhaust.
Hacksaw short shift, Momo race "s" carbon knob, ghetto rear strut bar, 16 inch cougar wheels with 225/50/16 kumho 712s
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Originally posted by Kaiser.: I have dyno'd with and without cats without this huge difference of which you speak.
The Wideband read the same with or without cats? That's not really possible since the cats scrub out unburnt fuel. Even if not 100% efficient they still would effectively lean out the mixture before the tailpipes. Unless of course the readings were always right around stoich??? If you mean you O2 voltage readings were the same with and without cats. I believe that since it is located upstream of them.. Though it probably should actually have leaned out a little with the better exhaust flow.
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Want to build your own wide band UEGO setup CHEAP? Look here: http://www.diy-efi.org/diy_efi/projects/diy_wb/ HTH Alex in Boulder, CO 95SE MTX 157hp 151tq before latest mods...
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If you mean you O2 voltage readings were the same with and without cats. I believe that since it is located upstream of them.. Though it probably should actually have leaned out a little with the better exhaust flow That is what I meant...obviously not what you meant. I think that you are implying that all the tuning I did with the wide band O2 in the tail pipe was wrong?
If it's true that we are here to help others, then what exactly are the others here for?
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Originally posted by Kaiser.:
That is what I meant...obviously not what you meant. I think that you are implying that all the tuning I did with the wide band O2 in the tail pipe was wrong? Tuning on a dyno is never wrong as long as the dyno shows improvements.  (Heck even losses as they tell you what NOT to do again  ) I'm just saying the A/F ratio the wideband was reading was not the same as the ratio the first O2 sensor was reading when you had cats. In other words it was not a true representation of how rich the car was running. (being lean would always show up since the cats can't scrub what's not there) Once you removed all the cats the wideband for the most part read the exact same as it was directly out of the engine.
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Originally posted by DemonSVT:
Once you removed all the cats the wideband for the most part read the exact same as it was directly out of the engine. Except for the lag time in the A/F vs. RPM graph, from the time for the gasses to reach the back of the exhaust system. I dunno how fast the exhaust gas moves or if it makes any difference, but it seems to me (uneducated guess) that the closer you were to the exhaust valves the more accurate your A/F will be when plottd against RPM.
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Originally posted by PA 3L SVT:
Except for the lag time in the A/F vs. RPM graph, from the time for the gasses to reach the back of the exhaust system. I dunno how fast the exhaust gas moves or if it makes any difference, but it seems to me (uneducated guess) that the closer you were to the exhaust valves the more accurate your A/F will be when plotted against RPM. That's a very good point. Anyone have a radargun to clock the exhaust velocity??? Also would not larger pipe equate to more lag then. With that noted - I'm sure at medium to high rpms the lag is pretty short.
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The dyno I use you can see the air/fuel. When the secondaries open there is a bump in the torque horsepower. There also is a bump in the air fuel being that there is more air rushing in. This is how I gauge the speed. It is about 200rpm off.
If it's true that we are here to help others, then what exactly are the others here for?
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My "friends" has no pre-cats or cat.
It was dynoed on a dynojet and a/f ratio probe was inserted into the tail pipe.
I hooked up the obd-ii datalogger to my laptop.
My results are .88v is 13.9 a/f and .86v is 14.3 a/f and .93v is 12.1 a/f.
So interpolated...
.87v = 14.3
.88v = 13.9
.89v = 13.5
.90v = 13.1 +-.1
.91v = 12.7 +-.1
.92v = 12.5 +-.2
.93v = 12.1 +-.3
S-AFC and redyno soon.
98 Contour LX V6 Mtx
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