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Speedo, MPG and tire size

Discussion in 'General Jeep Discussion' started by Billy1234, Apr 28, 2017.

  1. Apr 28, 2017 at 5:45 AM
    #1
    Billy1234

    Billy1234 [OP] Well-Known Member

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    I didn't realize this til now but I get about 11 miles per gallon if I calibrate my speedo to the 35. Will that get better?
     
  2. Apr 28, 2017 at 7:11 AM
    #2
    OFFGRID

    OFFGRID Well-Known Member

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    Howell fuel injection, header, HEI distributor, TH350, NP208, SOA lift with YJ springs in the front & GW springs in the Rear. AMC20 with G2 1 piece chromos trussed, Dana 30 with G2 chromos and 760x ujoints and MM Stainless Hubs, Geared 4.56. Tom Woods shafts, Metal cloaks, Caged, 37" Toyo MTs.
    Yes. Going bigger tires without calibrating tricks the computer into thinking you are traveling less miles per gallon. Made up numbers for ease. 31s make 100 revolutions per mile (RPM), and 35s make 75 RPM The computer will still count 100 RPM on the bigger tire and call it 1 mile. Therefore on the display losing 25% of your mileage. (numbers are off but the principle is the same).
     
    JKBob 25, aggrex and chris4x4 like this.
  3. Apr 28, 2017 at 8:41 AM
    #3
    Billy1234

    Billy1234 [OP] Well-Known Member

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    Thank you so much for the help maybe ill get more then 11 mpg lol
     
  4. Apr 28, 2017 at 8:43 AM
    #4
    Billy1234

    Billy1234 [OP] Well-Known Member

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    Any chance you'd be able to find a link to a good one? I have no clue what to look for.
     
  5. Apr 28, 2017 at 9:49 AM
    #5
    OFFGRID

    OFFGRID Well-Known Member

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    Howell fuel injection, header, HEI distributor, TH350, NP208, SOA lift with YJ springs in the front & GW springs in the Rear. AMC20 with G2 1 piece chromos trussed, Dana 30 with G2 chromos and 760x ujoints and MM Stainless Hubs, Geared 4.56. Tom Woods shafts, Metal cloaks, Caged, 37" Toyo MTs.
    I have always used hypertech. Mine will recalibrate tire size and gear ratios. There are many out there and if you are only changing tire and/or gear ratio I don't think it matters what brand. It is when you start using tuners that also accommodate tire size and gear ratios and are tuning the motor and trannys that I would pay more attention to brands like Banks, Hypertech, Superchips, and others.
     
    Billy1234 [OP] and JKBob 25 like this.
  6. Apr 28, 2017 at 6:44 PM
    #6
    JKBob 25

    JKBob 25 Well-Known Member

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    Great posts OFFGRID. I personally use a Superchip. It's definitely worth the 180 bucks.
    When I was running the stock 225/ 16s. I was getting 20 plus mpg. When I upgraded to the 305 /17s I'm running now. I reprogramed the computer for them. At 65 mph, I dropped my rpms by about 200 to 250. And I'm getting 19 plus mpg.

    So a reprogrammer is worth the moneyear. I picked mine up from Quadratec
     
    Billy1234 [OP] and aggrex like this.
  7. Apr 29, 2017 at 10:51 AM
    #7
    Billy1234

    Billy1234 [OP] Well-Known Member

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    Would this be a good one to go with?
    IMG_0922.jpg
     
    JKBob 25 likes this.
  8. Apr 29, 2017 at 12:24 PM
    #8
    OFFGRID

    OFFGRID Well-Known Member

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    1979 Jeep CJ7, 258, TH350, NP208
    Howell fuel injection, header, HEI distributor, TH350, NP208, SOA lift with YJ springs in the front & GW springs in the Rear. AMC20 with G2 1 piece chromos trussed, Dana 30 with G2 chromos and 760x ujoints and MM Stainless Hubs, Geared 4.56. Tom Woods shafts, Metal cloaks, Caged, 37" Toyo MTs.
    Looks good to me.
     
    JKBob 25 likes this.
  9. Apr 29, 2017 at 12:40 PM
    #9
    Billy1234

    Billy1234 [OP] Well-Known Member

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    Sweet thanks ordering it now
     
    JKBob 25 likes this.
  10. Apr 29, 2017 at 2:31 PM
    #10
    JKBob 25

    JKBob 25 Well-Known Member

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    That's what I have. Very simple to use. Just make sure you download the updates. Well worth the money

    Curious to know how you make out. Any questions, shoot me a pm.
     
    Last edited: Apr 29, 2017
  11. May 1, 2017 at 7:27 PM
    #11
    JKBob 25

    JKBob 25 Well-Known Member

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    Yo Billy. How did you make out with this?
     
  12. May 2, 2017 at 4:19 AM
    #12
    Billy1234

    Billy1234 [OP] Well-Known Member

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    Just waiting on it to come in should be here this week hopfully
     
  13. May 2, 2017 at 6:49 AM
    #13
    Billy1234

    Billy1234 [OP] Well-Known Member

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    It should actually be here by the 10th the a little better mpg for this guy! Instead of 10.5 lol i dont really mind bad gas milage but dam my lincoln ls got a little better then that
     
    JKBob 25 likes this.
  14. May 2, 2017 at 11:04 AM
    #14
    OFFGRID

    OFFGRID Well-Known Member

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    Howell fuel injection, header, HEI distributor, TH350, NP208, SOA lift with YJ springs in the front & GW springs in the Rear. AMC20 with G2 1 piece chromos trussed, Dana 30 with G2 chromos and 760x ujoints and MM Stainless Hubs, Geared 4.56. Tom Woods shafts, Metal cloaks, Caged, 37" Toyo MTs.
    You are not really getting bad gas mileage. Your computer just thinks you are. Look at it this way, at least the computer thinks that you are putting less miles on it than you really are.
     
    JKBob 25 likes this.
  15. May 3, 2017 at 12:24 AM
    #15
    Billy1234

    Billy1234 [OP] Well-Known Member

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    Oh ok thanks you guys are a great help
     
  16. May 3, 2017 at 12:05 PM
    #16
    Billy1234

    Billy1234 [OP] Well-Known Member

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    Jkbob my good buddy how far down did you actually go with the rpms? Mine are pretty low as it is i already got my superchip useing it as im posting this haha
     
  17. May 3, 2017 at 7:37 PM
    #17
    JKBob 25

    JKBob 25 Well-Known Member

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    At 65 mph, which is a good starting point. I went for about 2230 - 2250 to about 1900 - 1950 Still have very good acceleration and passing power. Now I could advance the timing a bit more. But I would be tricking the on board into thinking I'm running a different size tire than I actually am. But I know it would hurt my gas milage.
     
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