4107 thoughts

[RJ]

Art -

The loss in fuel economy you mention if using that (4905) final drive, would that disappear if you kept the speed down, or do you think it would be a wash regardless?

With the 4.375:1 rear end, you'll be running 100 rpm higher all the time compared to the stock 4.125:1, regardless of terrain.  So, you'll burn more fuel.  Simple.

The Ozarks and Appalachians are speed bumps compared to what we have out here on the West Coast, btw, and we did just fine with the OEM powertrain. . .  Just think of Aesop's Fable of the Tortoise and the Hare.

If I get on it at the bottom, the turbo is still not spooled up when the grade starts, and I stall to a stop momentarily right on the 18% part of the grade.

Try this:  At the bottom of the grade, hold the Bounder still with your left foot on the service brakes.  Floor the throttle till the turbo spools up, THEN let go and see if she "bounds" up your driveway.

Its just that those ginormous cargo bays and flat floor of the 4107 have me mesmerised.

Actually, the floor of the 4104/4106 is flat front-to-rear, compared to the stadium seating arrangement in the Buffalos, literally giving you more living space.  The wheelwell intrustions are only about 2" high, easily covered with furniture up front.  Lots of different ideas in the rear, from twin beds against the walls to a slightly raised floor have all been done. 

As I said before, you can level the front floor of a Buffalo, but if you're over 5'10", you'll bang your forehead on the Vista Windows framing.  And you still end up with less interior space.

I agree that the huge baggage bins, plus the pantograph doors, are a big plus for a Buffalo, especially the 4905s.  No other coach comes close, including a lot of the new 45-footers (w/ the exception of BK's new S-417 Setras).

OTOH, since you've said numerous times you want to "build it light", those enormous bays could work to your disadvantage, because you'd be tempted to carry a lot more "stuff", which equals weight. . .

Maybe all I need is a reality check?

Yup!   


FWIW & HTH. . .




PS:  Suggest you start a new thread for the HVAC stuff, rather than having it get lost in this one.

[RoyJ]

  I dont believe there is any loss of torque through a drivetrain such as there is with horsepower. Ive been asking that question for over 20 years and always get the same answers, no loss of torque. But that could be wrong information, or, my assumption would be some loss at higher speed. In first gear and under 10 mph, the gear box and axle are turning so slow I doubt any loss would be significant. But again, its a grey area that tends to minimise performance.
  Yes, the jeep is a 4.0, plenty of power.
 

Not showing off here, but just so you know my background, I'm a Mechanical Engineer.

The hp formula is:  rpm x torque / 5252. If there's no loss in torque, how can there be loss in hp?

The primary loss of a transmission is friction of the gear mesh process. The amount of torque lost is proportional to the torque input to the transmission. In other words, 15 lb-ft loss with 100 lb-ft input, and 45 lb-ft of loss with 300 lb-ft input.

Because the primary loss of a transmission is frictional, rather than viscous, its loss is therefore the same regardless of rpm or vehicle speed. In fact, 1st gear would have the MOST losses, due the the greater difference in gear diameters. Like wise, direct drive has the least losses. You can even measure the stall torque at the wheel, and it'll be the same 15% (or even higher, as static friction is higher) as if the bus were rolling.

[RJ]

Roy -

Great info!

Quick question:

In other words, 15 lb-ft loss with 100 lb-ft input, and 45 lb-ft of loss with 300 lb-ft input.

This is an example of the proportional loss, correct?

Not the actual loss we poor GMC folk suffer from with our convoluted V-drive layouts?

TIA!

[Rick59-4104]

Artvonne,
You are just a little over an hour from me, I am just off Ar Hwy 43 between Harrison and Compton. If you want to see my 4104 my cell is eight-seven-zero-4-1-6-sixty-4- twenty. If you want to come over give me a shout and we can get together on a day and best time.

Rick

[steve wardwell]

are you tempted to try that driveway ? (bring a camera)  lol  I just might to see this.....sorry   sorry    sorry.......You  know my wife has never gone up our little hill with me?  by the way her eyes can sure get real big when i do this crap  lol

[zubzub]

are you tempted to try that driveway ? (bring a camera)  lol

And a  nice beefy tractor. 

p.s. make sure you have lots of memory and batteries for the camera...I'm thinking youtube.

[TomC]

Based on RJ's 14.265 overall gear ratio in 1st, the maximum 760lb/ft torque (with 60 injectors), and 485 rpm 12R-22.5 rubber weighing 28,000lbs, your gradeability (not startability) will be 17.5%.  If you turbocharged the engine like mine is with 1125lb/ft torque your in motion gradeability rises to almost 26%.  Torque makes a big difference.  Good Luck, TomC

[RoyJ]

Roy -

Great info!

Quick question:

In other words, 15 lb-ft loss with 100 lb-ft input, and 45 lb-ft of loss with 300 lb-ft input.

This is an example of the proportional loss, correct?

Not the actual loss we poor GMC folk suffer from with our convoluted V-drive layouts?

TIA!

Yeah that was purely an example. Reason being the typical counter-argument:

If a 300hp engine looses 30hp with a certain transmission, and you hook that same transmission to a 600 hp engine, wouldn't it also loose 30hp?

Now I don't know much about the V-drives, but if I understand correctly, that's another set of gears (to change engine rotation orientation) in addition to the gear box and diff? If so, then 15% loss would definitely be quite possible!

[RJ]

Roy -

Now I don't know much about the V-drives, but if I understand correctly, that's another set of gears (to change engine rotation orientation) in addition to the gear box and diff? If so, then 15% loss would definitely be quite possible!

Perhaps this will help you visualize the GMC V-Drive.  It is "flopped" from the actual orientation, but you'll get the idea.  (I actually got it oriented correctly in my photo editing software, but you couldn't read the notations!)  In your mind, "roll" the engine assembly over the rear axle so that the transmission bevel gear is in the lower RH corner, and you'll have the proper layout.

[artvonne]

The hp formula is:  rpm x torque / 5252. If there's no loss in torque, how can there be loss in hp?

  That formula is too simplistic really. First of all, that is only refering to brake HP at the crank. To find road HP at the wheels the device would have to be tested at the output end and compare this with power tested at the input end. Whether that would prove loss of torque through friction, or only a drop in HP is a very deep subject. So many of the greatest minds have attempted to explain it, so many times, that the entire subject is filled with controversy and error.

  I do recall an engineering professors explaination quite clearly. If you apply torque to the crankshaft pulley nut, and measure torque at the output end, is there any loss due to friction? No, there is only the division or multiplication of the gearing ratios. Of course, that is in a static environment, not dynamic, and as you say, this creates other forces.

   In any case we can see that its ability to make an 18% grade is borderline. I found the discussion quite enlightening, and I hope everyone else did as well.

[uncle ned]

Artvonee

come to NC and try my 04.  It would have no trouble with your drive way.

uncle ned

[RoyJ]

The hp formula is:  rpm x torque / 5252. If there's no loss in torque, how can there be loss in hp?

 That formula is too simplistic really. First of all, that is only refering to brake HP at the crank. To find road HP at the wheels the device would have to be tested at the output end and compare this with power tested at the input end. Whether that would prove loss of torque through friction, or only a drop in HP is a very deep subject. So many of the greatest minds have attempted to explain it, so many times, that the entire subject is filled with controversy and error.

 I do recall an engineering professors explaination quite clearly. If you apply torque to the crankshaft pulley nut, and measure torque at the output end, is there any loss due to friction? No, there is only the division or multiplication of the gearing ratios. Of course, that is in a static environment, not dynamic, and as you say, this creates other forces.

First, no, that equation does not just apply to the crankshaft, or any specific power plant. It's based on the simple physics formula: power = force x velocity.

hp = 33000 foot pound / min = 33000 foot pound radians / min = 5252 foot pound rpm. Remember, 2pi radians is one rev, and 33000/2/3.14 is roughly 5252.

So, knowing this equation applies to ANY moving system, look at the terms. hp = tq * rpm / constant. Fix rpm and the constant, if tq doesn't change, how does hp? How can you possibly have a transmission that looses hp, but miraculous, keeps a constant tq?

Regarding your professor's example, I hope he made a genuine mistake, or else he shouldn't be teaching. Static friction is the greatest of all, this is why it's hard to get a car rolling, but much easier to keep it rolling. Likewise, it's much harder to get a gearbox (under torque transmission) rotating, than it is to keep it in rotation.

Picture this, if a box sitting on the ground has 50 lbs of friction, and you push it with 30 lbs, it won't move. Every body can picture this. But this is what gets confusing: if you push it with 100 lbs, and your friend is holding it on the other side from moving, what does he feel?

A) 100 lbs?
B) 50 lbs?


B) is correct.

Instead of you and the box, picture an engine and transmission. If you put 500 lb-ft into a transmission, and the net loss is 50 lb-ft, then the output shaft only feels 450 lb-ft, even if the bus is sitting still!!!

It's intuitive to think that under static conditions, a gearbox transmitt 100% torque, but it doesn't, it transmissits even lower. The gear teeth experience even more friction when they're sitting still.

[RoyJ]

double post

[zubzub]

I have really enjoyed this thread.

[buswarrior]

Anyone who has a chance to try to turn the shafts in a transmission by hand knows it takes some doing to make it spin. There's some gear meshing losses to be sure.

A friend had a roadranger case carved open, gears sets intact, as a display for teaching drivers, with a handle for spinning it.

Drivers weren't as rough, once they could see the internals moving, how the gears changed, and which bits they would be risking breaking through careless use.

But, it was a bear to get all those gear sets to spin.

happy coaching!
buswarrior