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Thread: Benefit to STABLE lower idle rpms? And question on truck intake marine IFR

  1. #1
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    Question Benefit to STABLE lower idle rpms? And question on truck intake marine IFR

    1. Currently I have my GMC Sierra 1500 rcsb cammed lq9 idling stable at 725 rpms once up to operating temp.

    I was wondering if there are any benefits to have a STABLE, lower idle rpm than that. Something like 600-650rpms.
    Would there be any noticeable mpg increase, or anything else worth note?

    2. My injectors are supposed to be 8.1 marine injectors, am I right by having my flat vacuum referenced IFR table at 43.8?

  2. #2
    Joe (Moderator) joecar's Avatar
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    1. 725 rpm is fine.

    2. what is their flow rating...? Yes flat.
    Last edited by joecar; September 15th, 2013 at 12:45 PM.

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    Quote Originally Posted by joecar View Post
    1. 72 rpm is fine.

    2. what is their flow rating...? Yes flat.
    1. So no real benefit to lower rpms at idle then?

    2. I bought them used so not totally sure. Think they are supposed to be between 42-44.

    Have it set to 43.8 and at WOT the afr was ~14.1

    I have stoich set at 14.026 for e10 and PE Fueling at 1.16 of eq

  4. #4
    Joe (Moderator) joecar's Avatar
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    Are they rated to flow 43 lb/hr at 3-bar or 4-bar...?

    Your rail pressure is 4-bar (58 psi)...?

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    Quote Originally Posted by joecar View Post
    Are they rated to flow 43 lb/hr at 3-bar or 4-bar...?

    Your rail pressure is 4-bar (58 psi)...?
    Ill have to look for the part number and look up the information.

  6. #6
    Joe (Moderator) joecar's Avatar
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    Measure your rail pressure (with manifold reference disconnected).

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    The marine injectors are rated at 43.8lb/hr at 4 bar. As I recall, those numbers are using regular unleaded gas, not E10.

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    Quote Originally Posted by Gordy M View Post
    The marine injectors are rated at 43.8lb/hr at 4 bar. As I recall, those numbers are using regular unleaded gas, not E10.
    Ok that sounds good.

    After correcting for my first calc.vet, today the afr is much more in line with accurate. So we'll see how the next wot run is.

  9. #9
    Joe (Moderator) joecar's Avatar
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    Ok, rated at 43.8 lb/hr @ 4 bar: so you're good to go, IFR table is flat 43.8 lb/hr all across.



    Also note: make sure your rail pressure measures 58 psi (4 bar) with FPR reference hose disconnected during measurement.

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