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Where's my sweet spot??

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Sumothertrucker, May 24, 2011.

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  1. May 24, 2011 #1
    Sumothertrucker

    Sumothertrucker Light Load Member

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    I asked my wife if she knew where my sweet spot was and she said after 25 years I still hadn't found hers so I was probably s### outta luck finding mine.

    No seriously. Got an 04 C15 thats been de-bridged an a PDI stage 1 down load from Master Haney. Runs 1375 at 65mph on 3:55's with a RTLO13 on 22.5 tall rubber.

    In the Quest for better mileage I'm wondering if 3:36's would help. As far as I know it should bring the rpm,s down to about 1275 at 65mph.

    Correct?

    Where is the optimum rpm for fuel mileage on a C15?
     
    Sumothertrucker, May 24, 2011
    Sumothertrucker, May 24, 2011
    #1
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  3. May 24, 2011 #2
    little cat 500

    little cat 500 Road Train Member

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    i don't think mine would even pull at them low rpm's im like 1550 at 65 around 6.5 on the fuel
     
    little cat 500, May 24, 2011
    little cat 500, May 24, 2011
    #2
  4. May 24, 2011 #3
    Sumothertrucker

    Sumothertrucker Light Load Member

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    :biggrin_2556:you must be in a knew space age aerodynamic truck aye?
     
    Sumothertrucker, May 24, 2011
    Sumothertrucker, May 24, 2011
    #3
  5. May 24, 2011 #4
    SHC

    SHC Spoiled Rotten Brat O/O

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    Westville, IN
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    I was just thinking about asking this same question. I have an 04 MBN as well, with 22.5LP.

    Also, how much did that tune help out, Mainly with mpg?
     
    SHC, May 24, 2011
    SHC, May 24, 2011
    #4
  7. May 24, 2011 #5
    little cat 500

    little cat 500 Road Train Member

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    im in a international 9900 with the tall top super ten 3.55 low 22's
     
    little cat 500, May 24, 2011
    little cat 500, May 24, 2011
    #5
  8. May 24, 2011 #6
    Sumothertrucker

    Sumothertrucker Light Load Member

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    I've only had the tune in 4 weeks. 2 weeks in high wind averaged a solid 5.8mpg. 2 weeks in decent weather was a solid 6.

    Also installed the FASS about 3 weeks before the tune but between the two the mileage is up about .8 per gal. It would only do 5.2 on it's best day before.

    It appears the FASS brought the mileage up .2 before the tune. But after the tune.....Yea baby....that's what daddy likes.:biggrin_255:
     
    Sumothertrucker, May 24, 2011
    Sumothertrucker, May 24, 2011
    #6
    SHC, Strider and The Challenger Thank this.
  9. May 25, 2011 #7
    Frenzy

    Frenzy Medium Load Member

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    Seattle, WA
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    I have a 2000 c-15, that was turned up (from 435) to 500 when the engine was rebuilt. I think the 500hp factory program was 1999 or earilier tune. I hardly ever run the engine past 1400 rpm. Most of the time I'm at 1200 / 55 mph (I drive most of my miles in Oregon). Engine pulls real good down to 1000 rpm, loses power below 950. If I was changing the rear ratio I would try to get it to be 1100 / 55 mph.

    My outbound loads are about 10K, returns maybe 1k. I've averaged 9mpg over the past 3 months. I expect to do a bit better if it ever warms up and stops raining.

    Some other things to do for improving mpg:

    drive the speed limit (not a few over), it's legal to do that.
    dynamic wheel balancers for the drives and the steers. (I use centramatics) about .25 mpg gain
    Air Tabs for the tractor. I got a solid .3 mpg gain.
     
    Frenzy, May 25, 2011
    Frenzy, May 25, 2011
    #7
  10. May 25, 2011 #8
    PaulE

    PaulE Medium Load Member

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    Verona Wi
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    Theres a difference between the "sweet spot " and where you can get best mpg. as long as your happy with the performance at 1275 rpm ( not a problem with the stage one )then your mpg should improve at the lower rpm. I would do it if it were mine.
     
    PaulE, May 25, 2011
    PaulE, May 25, 2011
    #8
    Sumothertrucker Thanks this.
  11. May 25, 2011 #9
    Sumothertrucker

    Sumothertrucker Light Load Member

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    I appreciate the information. I have the wheel balancers already.

    I guess what i was really looking for is what rpm that engine is designed to get the best fuel mileage at outta the box. Part of the reasoning is i would like to switch to lo/pros and wanted to make sure i get the right gearing figured out before the investment.

    I've been told anywhere from 1300 to 1500 is right for that motor and was just looking for some solid facts. I run about 65mph wich is the speed limit where I run. I've tried running slower but I just aint got it in me. Drives me nuts. What I would really like is to run 65mph at 1300 in 12th and still have a gear left to run 70mph (when the urge arises)and still keep the r'z down.

    I no I can get all the gear info from one of the on line calculators but wanted to make sure the I end up at the right rpm. Don't want to get the gears to tall that she falls on her face on the hills.

    I searched other threads on this sight but didn't find any solid answers.

    And as far as the mileage's i posted earlier, keep in mind this is on a "bridge motor" wich the timing is way more retarded than on an accert. So unless you have an 04' I wouldn't expect quite that good of increase if I understand everything I've learned fro Mr Haney.
     
    Sumothertrucker, May 25, 2011
    Sumothertrucker, May 25, 2011
    #9
  12. May 26, 2011 #10
    Mr. Haney

    Mr. Haney Road Train Member

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    You're in the sweet spot in my opinion for this engine. I've seen guys try to drop RPM with gear/tire changes hurt fuel mileage going lower than the RPM you're running at now, with the single turbo engines when grossed out on anything but flat ground. You have to realize as a single turbo, the turbo doesn't build boost like a set of twins would at low RPM. The turbo will get sluggish to respond and take extra fuel to drive the turbine wheel, EGT's will go up while cruising.

    If you were going to do a change it would be a 3.36 with low pro tires and the cruising RPM wouldn't change much for the 65 mph cruise speed. You can also run this engine up to 1450 RPM without much of a difference in fuel mileage for a slight increase in road speed.

    If I was going to spend any money on a parts for fuel mileage, I'd buy the camshaft, turbo and exhaust manifold. I have a customer that increased fuel mileage .3 mpg with the turbo and manifold change. I don't think you will see that kind of increase with the gear/tire change. I talked with a person that did the 800 hp marine cam in a MBN with a 7CZ flash that gained .7 mpg, I know you won't get that from the gear/tire change. I'm also going to say everybody's results are different on these part changes and your results could be the same or not.

    I feel these motors don't cruise well and get good fuel mileage below 1350 RPM on anything but table top flat ground with a tailwind at 80K gross weights.

    If you run light weights then you can slow the engine down another 75 RPM
     
    Mr. Haney, May 26, 2011
    Mr. Haney, May 26, 2011
    #10
    Sumothertrucker Thanks this.
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