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I want to finally get Gear Vendors unit, have questions though.

Discussion in '6.9L IH & 7.3L IDI Diesels' started by yARIC008, Dec 3, 2019.

  1. yARIC008

    yARIC008 Drives really slow

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    So currently the van has a 3.55 gear in the rear dana 60 differential. The tires I have on the van are 245/75/R16. Tread is still fairly new so that gives me a diameter of 30.46 inches on the wheel.

    Using the gear ratios for the E4OD from Gear Vendor's site
    https://www.gearvendors.com/fdrive.html

    and putting all the data in to here

    According to this website
    https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

    It says my engine should be spinning 1950 RPM at 70 MPH with the 3.55 gears and stock overdrive ratio of 0.71. I guess that's about right, my tachometer says otherwise but I think it's a little off. The math on the spicer site should be correct as it's, well... math.

    Anyway, if I put the Gear Vendors on right now with the 3.55 gear and the new double overdrive ratio of 0.55, my RPM would drop to about 1500 RPM at 70 MPH.

    According to our engine specs, we make peak torque of 338 ft-lbs @ 1400 RPM and the torque curve is relatively flat as RPM increase.

    At 1950 RPM the engine should max out at around 120 HP, at 1500 RPM the engine should be able to put out 94 HP. Problem is I don't really know what HP I need to keep rolling at 70MPH on a flat road. I'm guessing it is maybe somewhere around 50-60 HP but i might be completely wrong here. So it seems this might work ok...?

    However, I was now thinking to increase towing ease and maybe help performance overall, I would switch the rear gears to 4.10 and then install the Gear Vendor. That would put my cruising RPM at 1750 with the double overdrive. Max HP there would be about 108 HP.

    So question is, do anyone have an idea if cruising at 1500 RPM / 94 HP is too low? Will I get bogged down too easy?

    Using 4.10 gears, the 1750 RPM / 108 HP would give me a little more HP over the 3.55 and still give me a savings of about 200 RPM at 70 MPH so I'm guessing a good bump in fuel economy too.

    Any opinions?

    Thanks.
     
  2. hce

    hce So can i.... Supporting Member

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    Probably not much help but 3.55 zf-5 and gear vendors both in overdrive works well with a turbo for highway cruising. Don't ask about fuel mileage, I end up just driving faster with the gear vendors.
     
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  3. Black dawg

    Black dawg Registered User

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    I would give it a try with the 3,55 first and if it doesn't work like you would like, regear to 4.1.

    I had a 2wd suburban with 2.73 gears and 700r4,tbi 350, rpms were about 1600 at 70 and it worked ok, but didn't like to go much faster than that because of wind resistance and that low rpm. Mpg was 20+, highest I saw was 24, on the highway at 65ish. It was really quiet to drive.

    I would think a 7.3 would pull that rpm just fine
     
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  4. riphip

    riphip Supporting Member Supporting Member

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    I would leave as is with the 3.55 gears if you are not towing much. Remember, the horses here are not ponies but Clydesdales.
     
  5. chillman88

    chillman88 Supporting Member Supporting Member

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    1500rpm should be fine cruising on flat ground. I can run flat ground empty around 1000rpm. I wouldn't do it with a load, but I have 4.10s and can do 5th at about 32mph. If you're not planning on hauling much keep the 3.55s, you can always downshift. if you plan on hauling much then the 4.10s might be worth it.
     
  6. hce

    hce So can i.... Supporting Member

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    While driving home turning 1300 at 65 I had a thought. I backed off the cam for the advance or non advance, A little more timing at low end helps a lot with the loads of double overdrive.
    Second thought. I also have some special gearvendor e4od black box that I assume connects to the standard gear vendors controller and transmission cpu to make it all more seamless with the e4od in a box somewhere that will probably will never get used.
     
  7. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    I think your torque in more important for going down the road than your horsepower is. Also, don't you have an automatic in your van? If it does "get bogged down", won't it just down shift?
     
  8. yARIC008

    yARIC008 Drives really slow

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    Yeah, in theory it would downshift, but it'd be annoying if at every slight hill it'd be shifting up and down. Would rather not put unnecessary wear and tear on things shifting 100 times when it could shift 10 times.

    I'm a bit rusty on all my physics classes but the torque and the "power" output all play a part. Like I said the 7.3 IDI torque curve is pretty flat, looks like it goes from 338 ft-lb to like 320 ft-lb over the RPMs of 1400 to 3000. The higher it revs the more power output it has pretty linearly.
     
  9. yARIC008

    yARIC008 Drives really slow

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    I'm pretty sure when you buy the unit it comes with a controller interface thing.
     
  10. Oldiron

    Oldiron Full Access Member

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    Mine is set up 7.3, moose Jr IP, electric lift, ATS turbo, zf5, GV, 3.55

    Before the new IP, injectors, and elecrric lift pump, it was a turd and couldnt hold double overdrive at 80 mph.

    Now it does great. I would do 3.73 gears though, because I do tow sometimes
     
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  11. saburai

    saburai Supporting Member Supporting Member

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    What kind of boost are you running?
     
  12. Oldiron

    Oldiron Full Access Member

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    The most ive gottin is 11 psi.
     
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  13. saburai

    saburai Supporting Member Supporting Member

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    Do you have head studs? Even without, I think you'd be safe to turn the fuel up a bit to 14-15 PSI or so. if not, and you want to trade Junior for a baby, I'd be happy to oblige;)
     
  14. Oldiron

    Oldiron Full Access Member

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    To my knowledge no studs yet. And there is plenty of fuel. Need to install a fuel pressure gauge into my filter head and a regulator.

    Maybe someday run it on a dyno I and twerk timing. I set it at 9*
     
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  15. saburai

    saburai Supporting Member Supporting Member

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    So I'm assuming that you still have the wastegate hooked up. Apologies to the original poster for the hijack...
     

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