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Thread: Turning Up the Pump

  1. #31
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    Wes is right about fuel. The issue of RPM is more of a top speed and getting there thing (and getting the tranny to shift better). I've been down in muck and can't get it to spool up. It's a good and bad thing. I find myself backing in low TC range with a load and have to be in low to pull out. If I could get some power, I may be able to stay in high (backing up)...but I may have power to break the TC then too, when I back into the hole in low range. That darn TC problem is a limitation of the 929.

    Thanks Jbulach for the temp gauge link...I saw that one. There are several different ranges I noticed on pyro's. Looks like I should have 1800f even if I won't use the upper end, while 1300f might peg. When you mount the probe, where are you putting it? We did testing for UL and used to drill a small hole and glue the thermocouples in (a hundred or so). I'll use the probe in SS....my J TC is limited by using solder in the twist and won't work at that high temp. I'm thinking a wrap of high temp insulation over it, by the turbo. Do I really need the boost gauge?

    I'm working on the deuce so will rely on info here to get ready for these mods on the dump (accumulating parts). Thanks guys.
    Last edited by tobyS; 09-02-2019 at 09:02.
    M35A3 4x4 "Money Pit"
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  2. #32
    4 Star General Jbulach's Avatar
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    Default Turning Up the Pump

    Quote Originally Posted by tobyS View Post
    Wes is right about fuel. The issue of RPM is more of a top speed and getting there thing (and getting the tranny to shift better). I've been down in muck and can't get it to spool up. It's a good and bad thing. I find myself backing in low TC range with a load and have to be in low to pull out. If I could get some power, I may be able to stay in high (backing up)...but I may have power to break the TC then too, when I back into the hole in low range. That darn TC problem is a limitation of the 929.

    Thanks Jbulach for the temp gauge link...I saw that one. There are several different ranges I noticed on pyro's. Looks like I should have 1800f even if I won't use the upper end, while 1300f might peg. When you mount the probe, where are you putting it? We did testing for UL and used to drill a small hole and glue the thermocouples in (a hundred or so). I'll use the probe in SS....my J TC is limited by using solder in the twist and won't work at that high temp. I'm thinking a wrap of high temp insulation over it, by the turbo. Do I really need the boost gauge?

    I'm working on the deuce so will rely on info here to get ready for these mods on the dump (accumulating parts). Thanks guys.
    I have all the same problems off-road, and do the same with low range an such. But I want to do my mods in a logical order and see the results with real data for comparison.
    Yes, I can top 1300 with a good load, on big hills. I still need to change my alarm temp from 1100 to around 1275.IMG_6780.jpgThis is where I mounted my probe. I just went a little at a time with the tap until I could just get the straight threaded probe in without fear of twisting it off, and it sealed great. No, you donít need the boost gauge. Thats why I went real cheap, like $15, but found it nice to see that Iím getting exactly what most other people are reporting bone stock. I always wondered because I thought my truck accelerated exceptionally well while empty. The other thing is you can tell exactly when the pump de-fuels, and helps you learn how to max out your shifting RPM which in turn help you control your EGT, also why I want to see what a bit more RPM does for me. On that note, I would not Dick with your fuel until you get your low, max RPM issue figured out, if you haul heavy on the road at speed like I do. I think that would guarantee youíll burn your motor down if your short shifting and lugging with more fuel.
    M925A2

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    tobyS (08-30-2019)

  4. #33
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    I keep hearing that changing the timing to 16 degrees is the sweet spot for the 8.3. Is this correct? What are they set at stock? Thanks Jbulach for the photo of the prob location. I was wondering where everyone installs them at.

  5. #34
    4 Star General 74M35A2's Avatar
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    This one is a pump turn up thread, but........I got that # from a lot of study on RV boards. They are a large user group of the 8.3L and always in hard quest for more power and fuel mileage.

    If I remember correctly, our timing is a very conservative 10 degrees.

    The general consensus was that the largest single impact it has when done alone is fuel economy. From there, each power mod would have a larger effect once the timing was bumped. It also supposedly lowers EGT's. 16 degrees was the do-not-exceed value to keep reliability for stock 8.3L block/head/gasket/bolts. Besides the head gasket letting go, the block top deck surface on 1990 produced engines and slightly older are prone to cracking if pushed hard with very aggressive boost and timing figures.

    There are a few different ways to set it, detailed here in the 8.3L mod thread and the free online Cummins Quickserve parts and service web database. I don't think many here have done it, myself included, just studied deeply how to on all the several ways. A few here may have, but not many. You can do it in your driveway via injection pump gear clocking, or send your injection pump out and have the injection timing changed internally (easiest way, about $150, then pin time to re-install the pump, easy gravy job).
    Last edited by 74M35A2; 09-05-2019 at 13:37.
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