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Thread: Intake and Rocker Swap question with tune

  1. #1
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    Default Intake and Rocker Swap question with tune

    Pretty general qustion so I dont expect an answer that is "do exactly this' but rather where to start. Unless there is a def answer.lol
    Ok first one is the Cold Air Intake. Stock was a small airbox, flat filter and a tiny round hole in the end for air to enter. Now its a open conical filter on a smooth tube, with a larger behind the grille opening for a sort of ram air effect. I know more air is flowing.
    I had heard there is a rule of thumb 10% to 15% more airflow with a CAIntake. I dont trust just someones base opinion but rather like to gather many opinions/knowledge. Is that true or close to truth?
    I hear that the real effect of a CAI is lean since more air is added....but the PCM will sort of compensate and add fuel. But the Trims will read high. So fueling adjustments are nessesary. True?
    What fueling adjustments? VE Tuning alone or is there another Mixture Tab setting I should look into?

    The Second one is concerning a rocker arm swap. Larger Ratio. I know from stock SBC 1.5 to 1.52 isnt a huge jump, and honestly from 1.5 to 1.6 isnt that much either. Not like an all out cam swap anyways. But granted there is some changes, would you 'feel' the power band change especially if the tune is not correct?
    And what ina tune would you want to look at as a peramiter to change/adjust? VE again, cylinder dynamic, airflow, fueling, etc?


    thx for the input

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    anyone?

  3. #3
    Joe (Moderator) joecar's Avatar
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    Any changes to air flow/temperature would be seen by MAF/IAT, so PCM would take care of CAI (PCM computes a higher cylinder airmass based on MAF and IAT, so it adds more fuel to maintain the same AFR and reduces spark advance per the HO table)...

    CAI is not thought of as causing a lean condition.... it allows a slightly higher cylinder air fill to which the PCM responds with more air and less timing.

    I think a CAI gives 10%-15% only if the original plumbing allowed the passing air to get hot (e.g. IAT 72F vs 132F).

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    Joe (Moderator) joecar's Avatar
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    LS1 rocker arm ratio is 1.7 stock;

    actual VE would be effected, so you would have to edit the VE table;

    dynamic cylinder airmass is computed from VE;

    fueling is commanded from either of PE B3618, OLF B3605, or LTFT/STFT trimming, you would not change this.

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    Quote Originally Posted by joecar View Post
    Any changes to air flow/temperature would be seen by MAF/IAT, so PCM would take care of CAI (PCM computes a higher cylinder airmass based on MAF and IAT, so it adds more fuel to maintain the same AFR and reduces spark advance per the HO table)...

    CAI is not thought of as causing a lean condition.... it allows a slightly higher cylinder air fill to which the PCM responds with more air and less timing.

    I think a CAI gives 10%-15% only if the original plumbing allowed the passing air to get hot (e.g. IAT 72F vs 132F).
    Hmm ok, I had seen/read that it makes it inaccurate. But makes sense and I respect your input. Thx Joe for explaining it

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    Quote Originally Posted by joecar View Post
    LS1 rocker arm ratio is 1.7 stock;

    actual VE would be effected, so you would have to edit the VE table;

    dynamic cylinder airmass is computed from VE;

    fueling is commanded from either of PE B3618, OLF B3605, or LTFT/STFT trimming, you would not change this.
    I have a 4.3L 2003. Stock was the roller trunion 1.5 rockers with the Net Lash non adjustable. I installed the ARP rocker swap studs and a set of Comp Pro Magnum full rollers and they are 1.52. May do 1.6 later if I decide to not cam it. If I cam it then 1.52 I will keep.

    Point is I just need to complete the VE Tuning right?
    and if I swap cam or the rockers later do it again?

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    The ve and maf have to be tuned not just the ve tables. You can add +35% to the ve table at say 2200 rpms and your trims wont change at all. It is the maf sensor that is relied on to report airflow. Yes it is somewhat supposed to be a blend until 4000 rpm between the ve and the maf sensor. The ve table is a backup when the ecm goes into limp home mode, when the maf sensor goes bad.
    1997 S10, 06 trailblazer SS LS2 swap, 4L70E trans, 76mm turbo. Factory ZQ8 suspension. 3.08, G80 w/a zexel. With a 0411 swap.

  8. #8
    Joe (Moderator) joecar's Avatar
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    Yes of course, the MAF has to be corrected also (since the CAI duct has different geometry).
    Last edited by joecar; June 28th, 2012 at 11:53 AM.

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    Joe (Moderator) joecar's Avatar
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    Ah, you're talking 4.3L of which I know very little.

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    2003 4.3 so its like a 350 SBC minus 2 cyl and I have the 1MB PCM.

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