Announcement

Collapse
No announcement yet.

Gearing for optimal use

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Gearing for optimal use

    Transmission: It looks like I will go with the AX-15, thanks for all of those that pointed me in that direction. I will mate it up to the dana300, seems like the best route for my build.

    Gearing: I need help in this area! My jeep came to me with 3.23's in it from factory. I put 4.10's in it a few years ago and they have been fine for my application. With the Cummins R2.8 however it makes power really low in RPMs and I would like to keep RPMs at or below 2000 RPMs most of the time for fuel economy and good performance. Running the gear ratio calculator (link below) it looks to me like my RPMs at 70 MPH will be around 2309 (4.10 gears, 33" tires, .79 fifth gear). I'm thinking of going back to the 3.23's which would put the RPMs around 1819RPMs at 70MPH which I think would be okay but.. thoughts? In my RAM 2500 my RPMs are 1470 at 70MPH and it gets around 22MPG.

    I'm not really looking to get some ridiculous mileage I know this is a Jeep and low gears are good, Just looking for what is ideal for this engine. It should be noted that I drive about 6 hours to my wheeling/camping area so highway gears is useful.

  • #2
    What year is your Ram? If it's new, it most likely does a lot of shifting in and out of OD on the highway, assuming it's an auto. 1470RPM is great for fuel economy but you definitely wouldn't want to try and pass anybody without downshifting.
    My 2002 Dodge 2500 cruises close to 2000 RPM at highway speed in 6th (manual trans, 3.55 gears) and the only time I ever need to downshift is when the speed drops below 80KPH (yeah, I'm Canadian).

    In my personal opinion, you'd be much happier with 3.73 gearing if you're sticking with 33" tires, unless you don't plan on using 5th until you reach cruising speed.
    I've got 3.55's in my MJ and I'm going to start with 31's and see how it behaves. Maybe upgrade to 33's if the power is there. My first road test should be this weekend.

    Comment


    • #3
      My RAM is a 2017, I don't remember the gears but I'm thinking they are pretty high. It doesn't shift all that often unless i'm going up a grade and the grades here in California can be steep. I think what I'm looking for is information about where the engine (R2.8) operates best under load. I also want a balanced load and not load up the rear diff.

      Comment


      • #4
        Depending on the weight of your jeep anything below 1700 rpm isn’t ideal. Due to how the engine is tuned, try to stay above this rpm on the hwy for maintaining speed up grades. The ax15 is a great choice for trans, you will be happy. That said I would try the 4.10 gears but you may be happier with a 3.73 or 3.21.

        The RePowerToy runs about 2500 rpm at 75 mph, which is higher than desired. However when you point it up the mtns it goes without issue. I get 16-17 towing a 1700 lb trailer at hwy speed, and 19-22 unloaded.

        That said I would shoot for 1900-2200 rpm for 70-75 mph. Yes it does make to at 1500 but due to OFC in stock tune it doesn’t really like to pull grades at this rpm. My input is also just my opinion and based primarily on the altitude that I drive, 5000-12000 feet.

        And lastly Welcome!!

        Comment


        • #5
          Originally posted by RePowerToy View Post
          Depending on the weight of your jeep anything below 1700 rpm isn’t ideal. Due to how the engine is tuned, try to stay above this rpm on the hwy for maintaining speed up grades. The ax15 is a great choice for trans, you will be happy. That said I would try the 4.10 gears but you may be happier with a 3.73 or 3.21.

          The RePowerToy runs about 2500 rpm at 75 mph, which is higher than desired. However when you point it up the mtns it goes without issue. I get 16-17 towing a 1700 lb trailer at hwy speed, and 19-22 unloaded.

          That said I would shoot for 1900-2200 rpm for 70-75 mph. Yes it does make to at 1500 but due to OFC in stock tune it doesn’t really like to pull grades at this rpm. My input is also just my opinion and based primarily on the altitude that I drive, 5000-12000 feet.

          And lastly Welcome!!
          Thank you for the Welcome!
          Your advice makes sense. I am looking forward to taking this to my family cabin which is about 6 hours away. I usually have to tow it up but with this engine I'll feel more comfortable driving it up (reliability). I start at sea level in Ventura CA and end up in the high sierras so I think I'll run with the 4.10's and see how they perform. It's hard to beat 3.73's for every day use with an AX-15. I suspect as I get older the jeep my come back down from it's current height!

          Comment


          • #6
            from the performance calculator at http://lang.hm/scout/nph-performance6.cgi

            Comment


            • #7
              Good info!! The nerd in me loves seeing a graph for some of this.
              thanks

              Comment


              • #8
                that page is nerd heaven. I can add whatever other graphs or factors you want .

                I'm thinking of adding truck weight and % grade to the list to have it show how you do climbing a grade with the resulting 'thrust' value being how much power is available to accelerate you at that point. I just don't know if I should do another set of graphs, or have it be an option that modifies the existing ones.

                Comment


                • #9
                  I've been toying with gearing but my setup is not common since I am running portals with a 5.99 final ratio on 37" tires. Doing 75 is not a goal of mine as 60/65 is good enough for this vehicle. I've been running through wide ratios with various transmissions and this is what I get. Vehicle is 5400 lbs (unladen).

                  Paired to the LT230 with 1.03 high. Does the new 10/18 tune make any difference with the statement that anything below 1700 RPM is not really ideal or was that original tune?

                  ZF-S547

                  5.73, 2.94, 1.61, 1.00, 0.76, 5.24(R)

                  3MPH (850 Idle) - 10MPH (3000 RPM) - 1st

                  10MPH (1600) - 19MPH (3000) - 2nd

                  19MPH (1665) - 34MPH (3000) - 3rd

                  34MPH (1850) - 55MPH (3000) - 4th

                  55MPH (2275) - 73MPH (3000) - 5th

                  60MPH = 2481 RPM

                  ZF-S542

                  5.08, 2.60, 1.53, 1.00, 0.77, 4.66(R)

                  3MPH (850 Idle) - 11MPH (3000 RPM) - 1st

                  11MPH (1556) - 21MPH (3000) - 2nd

                  21MPH (1748) - 36MPH (3000) - 3rd

                  36MPH (1959) - 55MPH (3000) - 4th

                  55MPH (2305) - 72MPH (3000) - 5th

                  60MPH = 2514 RPM

                  Landy R380-44A (Stubby)

                  3.69, 2.13, 1.39, 1.00, 0.77, 3.42(R)

                  4MPH (850 Idle) - 15MPH (3000 RPM) - 1st

                  15MPH (1739) - 26MPH (3000) - 2nd

                  26MPH (1967) - 40MPH (3000) - 3rd

                  40MPH (2177) - 55MPH (3000) - 4th

                  55MPH (2305) - 72MPH (3000) - 5th

                  60MPH = 2514 RPM

                  NV4500

                  5.81, 2.94, 1.61, 1.00, 0.77, 5.69(R)

                  3MPH (850 Idle) - 9MPH (3000 RPM) - 1st

                  9MPH (1440) - 19MPH (3000) - 2nd

                  19MPH (1665) - 34MPH (3000) - 3rd

                  34MPH (1850) - 55MPH (3000) - 4th

                  55MPH (2305) - 72MPH (3000) - 5th

                  60MPH = 2514 RPM

                  Comment


                  • #10
                    the nv4500 ratios I find online are slightly different than what you are listing http://www.dieselhub.com/trans/nv4500.html

                    I added all the other transmissions and the LT 230 t-case into the calculatior, have fun.

                    Comment


                    • #11
                      Just an update if anyone is interested. I went with 3.55's and it's been great. I'm around 2K rpms at 70 MPH but as someone said earlier, this engine prefers to be at higher RPMs, at least above 1800 to 2000 rpms. I find if climbing a grade I'm better off at getting up to 75 then just pegging it, it will keep the speed and not have to downshift. 3.55's is a good set up for me, I like it and also gives me some play to go down a bit on tire size. I'm at 33's now and may lower the jeep a bit and go to 30's.

                      Comment


                      • #12
                        So, reviewing this calculator page, the torque and HP ratings of the R2.8 (230 & 118 respectively) I thought with the new tune the engine was more like 310/160. The reason I ask is that I am thinking go with the NV4500, since it is the only well supported trans that is rated considerably more than the Engine spec. (trans spec of 300 ftlbs on a 310ftlb motor, unmodified makes me a little nervous). Is there some magic torque/HP that I don't know about?

                        Comment


                        • #13
                          I think the NV4500 wouldn't be a bad choice, but it's a bit heavy and maybe overkill. I guess it depends on your driving habits and several other issues. I think the AX-15 or NV3550 would be adequate for this engine unless you get a hot tune, heavy with the accelerator or something.

                          My only issue with the AX-15 is that, I wouldn't mind a bit of a numerically higher 1st gear, but I'm very easy on my accelerator pedal and I've heard there may be some slight hesitation due to the EGR on take off, but I can't confirm that. I just happened to notice that take off seemed a bit harder than I expected when I was towing, admittedly too much for my application. In any case, since I think my transmission may have been the original transmission, then I've got 270k mi on it and I'm thinking of building/rebuilding a spare AX-15 with a numerically higher 1st gear. However when I swap my tcase to an atlas, I'll try messing with different maybe 3rd gear in 2lo for take off and then shift through a bit and switch back to 2Hi, if it's as smooth as it looks in some videos.

                          Comment


                          • #14
                            Originally posted by jeepCJ7 View Post
                            Just an update if anyone is interested. I went with 3.55's and it's been great. I'm around 2K rpms at 70 MPH but as someone said earlier, this engine prefers to be at higher RPMs, at least above 1800 to 2000 rpms. I find if climbing a grade I'm better off at getting up to 75 then just pegging it, it will keep the speed and not have to downshift. 3.55's is a good set up for me, I like it and also gives me some play to go down a bit on tire size. I'm at 33's now and may lower the jeep a bit and go to 30's.
                            I'm still currently at 3.07s, but I find the secret is just to be at around 1800 or more RPM, but to get my boost pressure up before I get into the hill. Personally I don't like being above 2k RPMs on the highway, but maybe that's because I'm going pretty fast with my gearing that way. My area is very hilly and I tend to like to run around 65, so I've certainly debated 3.73s, but I'd rather be under 2k rpms at 65 and then run 31s if I'm towing and need that extra grunt.

                            Maybe I missed it, but what lift size are you running? Do you know your vehicle weight?

                            Comment


                            • #15
                              The reason I was thinking the nv4500 over some of the lighter options is for potentially towing a smallish trailer (2500-3000#?) and for when the aftermarket does anything fun for the R2.8.

                              Comment

                              Working...
                              X