Cat c-15 high rpm?

Discussion in 'Peterbilt Forum' started by Dallison, Apr 1, 2021.

  1. Dallison

    Dallison Bobtail Member

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    Apr 1, 2021
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    I recently got a 2007 379 w/ a c-15 converted to single turbo. It has only been bobtailed so far but I was worried about how high it revs when I’m floating gears. Seems to idle just fine, but in the high side I’m having to get it to 17-19rpm for it to fall out the hole to upshift when floating. I’ve been told it needs a tune which I don’t doubt it needs updated fuel settings. I’ve also been told this rpm issue would change when I’m hauling. Just came here to get some input and direction before I get this thing on the road. Thanks!
     
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  3. AModelCat

    AModelCat Road Train Member

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    Not seeing the issue. Why can't you drag the RPM down further before you downshift? Problem solved.

    On that note, 1900 isn't gonna hurt a thing.
     
    Bean Jr. Thanks this.
  4. Dallison

    Dallison Bobtail Member

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    Apr 1, 2021
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    Downshifting seems fine, I was concerned because say going from 6th to 7th gear (13sp) if I’m floating the gears it won’t come out the hole until the rpms are up there. I’ve never had a cat but was always told they liked lower rpms. I’ve been driving a Cummins and have never had to take it past 1700 rpms to get it out of gear when upshifting. I just didn’t want to hurt anything running this motor like that so thought I should ask.
     
  5. Cat sdp

    Cat sdp . .

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    Orion's Belt
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    Halfass put your foot on the clutch when your pulling it out of gear...........then float it in....

    Cats don’t like low rpms especially jacked up ones. Think Heat in heat out ,rpms keep the air moving
     
    Last edited: Apr 2, 2021
    Bean Jr. Thanks this.
  6. skallagrime

    skallagrime Medium Load Member

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    Try giving it some fuel, then pull out of gear as you let up on the go pedal.

    1700 is a bit high for my taste, despite what these other guys are saying. (Yes it probably wont hurt it till about the 2k + mark, but stock setup runs good torque to 1400 and good hp to 1700 then each falls off pretty bad. If youve done much other than the turbo changeover, ignore everything i said, but my 3406e (485hp) and c15 (500 hp) are far happier at low rpm
     
  7. Dallison

    Dallison Bobtail Member

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    Apr 1, 2021
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    ok thank you! I know the pistons were changed to 16:1 but I’m not positive in anything else. I will likely take it someone to plug into the ecm and see if there’s anything to be done. It had a new clutch put in a few months before I got it but idk if that would have anything to do with it
     
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