Question when tuning
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  • 2 Post By EdwardETraylorIII
2009-2014 Cadillac CTS-V Performance Mods Discussion, Question when tuning in Cadillac CTS-V Series Forum - 2009-2014; Where is it better to monitor the A/F ratios of the car's exhaust, right off the header or the tail ...
  1. #1
    Luna. is offline Cadillac Owners Connoisseur
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    Question when tuning

    Where is it better to monitor the A/F ratios of the car's exhaust, right off the header or the tail pipe?

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    EdwardETraylorIII is offline Cadillac Owners Fanatic
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    Re: Question when tuning

    The closer to the source the better! I assume you're installing a wideband? I wouldn't use the OEM narrow-bands for any real tuning.............. Good luck my friend!

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    Luna. is offline Cadillac Owners Connoisseur
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    Quote Originally Posted by EdwardETraylorIII
    The closer to the source the better! I assume you're installing a wideband? I wouldn't use the OEM narrow-bands for any real tuning.............. Good luck my friend!
    Any concern that we aren't driving the car open header vs. with exhaust installed?

    I inquire as my A/F ratios seem to be different when analyzed/tuned right off the header vs. tailpipe and the tailpipe was much richer (I could understand leaner, but not richer). When the "tailpipe" tune was leaned out, my car made significantly more rwhp/rwtq. This has seemingly happened two times.

    I keep being told that off the header is superior, but I'm now wondering/confused.

    EDIT: Mistype above--should read much leaner instead of much richer

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    Rock1 is offline Cadillac Owners Fanatic
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    Re: Question when tuning

    Quote Originally Posted by Luna. View Post
    Any concern that we aren't driving the car open header vs. with exhaust installed?

    I inquire as my A/F ratios seem to be different when analyzed/tuned right off the header vs. tailpipe and the tailpipe was much richer (I could understand leaner, but not richer). When the "tailpipe" tune was leaned out, my car made significantly more rwhp/rwtq. This has seemingly happened two times.

    I keep being told that off the header is superior, but I'm now wondering/confused.
    Its always better to go as close to the source as possible, I've been told that this can be inaccurate and depending on how they attach the sniffer can be out of the flow of the exhaust (against the side) or can fall out, giving you inconsistent readings. It's also after the catalytic converters so that will affect the readings as well. Also I have seen it where in the higher RPM the tailpipe read richer then the WB and I have seen it where it is the same. This just shows that there is a variance in the 2 options.

  6. #5
    EdwardETraylorIII is offline Cadillac Owners Fanatic
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    Re: Question when tuning

    Any concern that we aren't driving the car open header vs. with exhaust installed?
    Yes, absolutely, you should have a tune for each - one for open header and one for exhaust installed. These exhaust dynamics can drastically effect your tune/power output.

    I inquire as my A/F ratios seem to be different when analyzed/tuned right off the header vs. tailpipe and the tailpipe was much richer (I could understand leaner, but not richer). When the "tailpipe" tune was leaned out, my car made significantly more rwhp/rwtq. This has seemingly happened two times.
    This doesn't really sound that far out to me given we really don't know what your cats could be doing, variance between one wideband and the other, and we all know leaner means more power (but not necessarily safely! lol).

    I keep being told that off the header is superior, but I'm now wondering/confused.
    Do not be confused - closer to the primaries the better. There are no exceptions to this rule.
    Dale Pittman and Dale Pittman like this.

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    Luna. is offline Cadillac Owners Connoisseur
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    Re: Question when tuning

    Quote Originally Posted by EdwardETraylorIII View Post
    Yes, absolutely, you should have a tune for each - one for open header and one for exhaust installed. These exhaust dynamics can drastically effect your tune/power output.
    This makes perfect sense to me

    Quote Originally Posted by EdwardETraylorIII View Post
    This doesn't really sound that far out to me given we really don't know what your cats could be doing, variance between one wideband and the other, and we all know leaner means more power (but not necessarily safely! lol).
    Fu*k me running...

    I misspoke. The car was LEANER with the exhaust installed, like 12.5 or so, and we had to adjust it (richer) down to, say, 11.9, as shown in my previously attached dyno graph.

    Apologies, I typed that out backwards.

    Quote Originally Posted by EdwardETraylorIII View Post
    Do not be confused - closer to the primaries the better. There are no exceptions to this rule.
    Yet one would still want to tune with the exhaust on, yes?

    As such, am I correct in saying that the "best" answer is to simply tune to how you are going to run the car?

    In other words, if I'm at the track running open header, run a tune specifically designed for that. If I'm running the car on the street, with full exhaust on, the car should be tuned that way.

    It seems strange to me to tune the car off the header, then install the exhaust and call it good to go under the premise that tuning off the header is the preferred method; I'm not driving the car open header, I'm driving it with the exhaust installed.

    Is my understanding correct?

  8. #7
    EdwardETraylorIII is offline Cadillac Owners Fanatic
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    Re: Question when tuning

    Yet one would still want to tune with the exhaust on, yes?

    As such, am I correct in saying that the "best" answer is to simply tune to how you are going to run the car?

    In other words, if I'm at the track running open header, run a tune specifically designed for that. If I'm running the car on the street, with full exhaust on, the car should be tuned that way.

    It seems strange to me to tune the car off the header, then install the exhaust and call it good to go under the premise that tuning off the header is the preferred method; I'm not driving the car open header, I'm driving it with the exhaust installed.

    Is my understanding correct?
    Yes... And now I see where your confusion is... Everything you say above is CORRECT. Here's the little bit you're missing that's causing you angst...

    A lot of dyno shops will put a bung in the collector (upstream of the cats) to screw their wideband into even with the mufflers on the car (or mufflers off if it's an open-header car) for a more accurate reading. Does this make a little more sense now?

  9. #8
    DSteck is offline Cadillac Owners Member
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    Re: Question when tuning

    Sounds like your air metering isn't calibrated properly. Ripping exhaust off shouldn't impact your AFR unless your wideband is too close to the end of the exhaust with the open headers. You usually need at least three diameters of pipe after the sensor to help prevent ambient air from skewing the readings.

    You can usually get away with a little more timing with open exhaust since you can evacuate it faster.

    Never use a tail pipe sniffer.

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