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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. BlackNoma

    BlackNoma Full Access Member

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    I ran my GV behind my c6 with 3.55 gears for almost 2 years. I had it set to engage at 55mph like a 4th gear. It made the c6 tolerable.
    I recently swapped to the zf5 and kept my GV. double OD running 85 im turning 2,000rpm. 18mpg.
    at 2,000rpm I would have to downshift to keep speed going up a large overpass/hill. Small ones were no problem. My truck is no power house, stock reman crap ip, ats 88 turbo (non wastegated).
    I would think turning lower than 2k you would be fine on flat ground. I think hills/overpasses would cause the trans to downshift.
     
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  2. FordGuy100

    FordGuy100 Registered User

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    "When a car moves along a flat road the engine has to work to overcome two main resistances - air resistance and rolling resistance (the drag in tyres, wheel bearings etc). The top speed of the car is determined by the amount of engine power available and the size of these retarding forces. The math to work out these equations for an actual vehicle are very simple. In order to calculate the top speed we need to work out the size of the retarding forces.

    ROLLING RESISTANCE
    Defined as the force needed to just start a car rolling on flat ground this force is mainly a function of vehicle weight. You can measure it yourself fairly easily with a pair of bathroom scales or a spring balance. Just hold the scales vertical against the rear bumper and push until the car starts to move. You might find that once the car is rolling the force needed to keep it just moving falls slightly. This lower force is the number you are after. For most cars the force in pounds can be estimated as follows:
    Rolling resistance (lbs) = vehicle weight (lbs) x 0.012 to 0.015 (I usually take 0.013 as a good average)
    Obviously if the tyres are flat or a wheel bearing is half seized this force can alter a fair bit but we will see later that it is air resistance that is the main obstacle to top speed so even a large error in the rolling resistance calculation won't matter much. Rolling resistance is taken to be a constant i.e. not varying with vehicle speed although this is really somewhat of a simplification. For an average car weighing 2500 lbs this force is therefore in the region of 33lbs.

    AIR RESISTANCE
    This is a function of the frontal area (fA) of the car and its coefficient of drag (Cd). Often car magazine tests show these numbers and all manufacturers will have the data if they can be persuaded to release them. Most modern cars have drag coefficients between 0.3 and 0.4 with a few really streamlined ones as low as 0.28 or so. The Cd is a measure of how "slippery" a shape is as the air goes round it.
    Frontal areas tend to lie between 19 and 23 square feet for European cars (we can exclude 4 wheel drive yank tanks and similar from this exercise because who cares how fast they go anyway?)
    The drag in pounds goes up with the square of speed and can be calculated from the following formula:
    Air resistance (lbs) = fA x Cd x 0.00256 x speed squared (speed in mph)
    Average family cars have a top speed of 120 mph or so these days so let's have a look at the size of this force at that speed. We'll assume the car has a frontal area of 21 square feet and a Cd of 0.35
    Air resistance (lbs) = 21 x 0.35 x 0.00256 x 120 x 120 = 271 lbs (at 120 mph)
    As you can see this is a much larger force than the rolling resistance. In fact rolling resistance only makes a major difference to vehicle dynamics at very low speeds (under 60 mph or so) and means that heavy cars use more power and therefore have poor fuel consumption at low speeds. At higher speeds the air resistance becomes paramount and so even heavy cars can show good fuel consumption if they are well streamlined.

    POWER REQUIRED
    The final step is to relate the drag figures above to the power required to overcome them. If we add rolling resistance and air resistance together we get total drag in pounds. Power required is then calculated as:
    Power (bhp) = Total drag x mph / 375
    We could if required split the power into the amounts needed to overcome each drag separately. The equations would then become:
    Power to overcome rolling resistance = weight x 0.013 x mph / 375
    Power to overcome air drag = fA x Cd x 0.00256 x mph cubed / 375
    Hopefully something of major importance should be clear from the above. We already know that it is air resistance that is the major element in this equation and we can see that we need to incorporate mph cubed in the power equation for air drag. As a simplification therefore we can say that power required is closely related to mph cubed - i.e. to double the speed of a vehicle we need 8 times the engine power. Alternatively we can express this as top speed is a function of the cube root of engine power. This means that engine modifications will have a much greater impact on acceleration (which is directly related to power) than top speed. Also that is why an old engine which is down on power might accelerate slowly but still have close to its original top speed. So next time your mate tells you in the pub that he put a K&N air filter in his car and the top speed went up by 10 mph you can explain exactly why that isn't going to be very likely.

    Examples:
    Let's say we want to increase the top speed of a car by 10% - how much extra power do we need? Increase in power required is related to increase in speed cubed - i.e. to 1.10 cubed = 1.33. So we need about 33% extra power to achieve 10% increase in top speed.Alternatively let's say we tune an engine and achieve 10% extra power - how much will top speed go up by?. Speed is proportional to the cube root of power - i.e. to the cube root of 1.10 = 1.03. So speed will only increase by about 3%.
    What this all means for you hopefuls who bolt on go faster goodies like chips, exhausts and the like. You will see hardly any increase in top speed. To get significant increases in top speed requires serious engine surgery.

    IMPORTANT NOTE:
    The power calculated above is power delivered to the wheels and NOT flywheel power - i.e. we need to allow for transmission losses to get back to engine power required. Transmission losses will be the subject of another article but for brevity we can take the following as good assumptions. Front wheel drive cars will lose 15% of the engine power as transmission and tyre losses and rear wheel drive cars will lose 17%. This assumes manual gearboxes and I could care less how fast autos or 4 wheel drive cars go !
    So divide by 0.85 or 0.83 as appropriate to convert from wheel bhp to flywheel bhp."



    Cant find any drag coefficents for an econoline. Buses are .6-.8, trucks (I assume tractor trailer) .8-1.0, so perhaps .8 is a reasonable guess. Based on 80" wide, 84" tall (per wikipedia) frontal area = ~47 sq ft (assuming flat faced, no idea if thats correct), 6500 lb van, .8 coefficient of drag, we get 112 hp @ 70 mph. This seems overly high, so I would think my guesstimates are off quite a bit.


    EDIT* Apparently frontal area is usually max width x max height x some factor (I suppose this would take into account area under the grille, slopped front glass etc). A .85 factor here would bring down HP to 92-93 hp @ 70 mph.
     
    Last edited: Dec 4, 2019
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  3. u2slow

    u2slow Plan B

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    Find out what minimum rpm the lockup and OD require to function and last. This is almost famous in cummins circles. Guys want low rpm cruise, but the auto-trans don't put up with it well.

    Based on my experience, I'd sooner make the van 5 speed and skip the gearvendors. Add 31-33" tires for more speed (only required on the rear).
     
  4. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    So how did you do this? Did it bolt to the back of your transmission?
     
  5. yARIC008

    yARIC008 Drives really slow

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    Thanks for the analysis. I guess we know for sure the upper bounds of the power required to keep it rolling is at least less than 120 HP as that's all the engine can make currently at 1950 RPM. The estimate of 92 HP might be accurate which would mean running at 1500 RPM would be RIGHT on the line of doable on flat ground with the engine making about 94 HP. Any hill and it'd probably have to shift.

    So I guess what the probably means is that I should rig up the Gear Vendors with the 3.55 gears knowing that I will most likely need to put in 3.73 gears to prevent lots of shifting.
     
  6. Black dawg

    Black dawg Registered User

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    So where do you find this min rpm info on an e4od?

    Going from e40d to zf would require almost 35 inch tires to maintain the same rpm as with the e40d. .71 vs .76 od ratio
     
  7. u2slow

    u2slow Plan B

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    Probably best to talk someone who builds E4ODs. I think it depends largely how loose/tight your TC is. Things won't last well if you're asking the lockup to 'eat' a significant rpm difference on engagement.

    Only comparable if you can stay in lockup, in OD, most of the time... vs the manual trans being in 'lockup' all the time.

    Bottom line is I'm a seasoned cheapskate. ;Really I just want to see folks do enough homework before they part with their hard-earned cash.
     
  8. yARIC008

    yARIC008 Drives really slow

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    I've got a manual lockup switch rigged up to the TC lockup. Generally, you can kinda tell when it doesn't like being locked up, such as when you drop the engine RPM too low or bog it down to much, it kinda starts sounding like it's grinding... which it probably is. I don't know how the TC physically actuates the lock up clutch, if it's electrical driven or fluid pressure driven inside the TC, never rebuilt the trans or studied it enough. If it's fluid pressure i'd think there is some minimum RPM the TC would need to spin to make it lock up 100%. If it's some solenoid or something then I'd guess it might not matter.
     
  9. snicklas

    snicklas 6.0 and Loving It!! Staff Member

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    I'm 99.9% sure its hydraulic pressure that caused the lockup. It's controlled by a solenoid, but it fluid doing the lockup. @trackspeeder could probably answer some of these questions......
     
  10. typ4

    typ4 Supporting Member Supporting Member

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    A torque cam will be an immense help in this situation.
     
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  11. VanDiesel

    VanDiesel Registered User

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    85 E250 Club Wagon with 93 7.3, C6 with GV and 3.55 gears, somewhere around 20 mpg at 60
     
  12. jaluhn83

    jaluhn83 Full Access Member

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    The lockup is a hydraulic clutch within the TC. It's electronically controlled through a solenoid valve, thought typically with hydraulic interlocks as well. Pressure come from the main front pump that also supplied all the other hydraulically actuated clutches & brakes within the trans. The engine rpm shouldn't really impact TC clutch force unless you're lugging it way down (like 1000 rpm). What does have impact is the torque rise of the engine and probably the increased torsional vibration at low rpm.
     
  13. BlackNoma

    BlackNoma Full Access Member

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    Sorry this is late

    My truck is 4wd, so i just kept the t-case that has the GV bolted to the back of it. Only works in 2wd. 4wd will go bang. haha
     

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