Starting to commence to think about 4x4-ing Candy Van. It's already AWD, so in theory it's just a transfer case and a front driveshaft away from having real 4x4.
So I'm mathing to find out how much torque I can realistically give the 7.2" front diff. A couple sources say that the diff can take a pinion torque of 2333 ft-lbs. Since the current viscous AWD box is set for about a 40/60 split and has no low range, I'm sure the 7.2" is adequate.
So: LM7 5.3L makes 315 torques, but I'm going to round it up to 350 to be safe and because I might do a tune and exhaust some day.
350 torques * 3.06 first gear * 2.78 xfer case low range = 2935 torques on paper.
Divided that by two since it is a 50/50 torque split = 1467 torques.
Where I'm having trouble is the two huge question marks of A) how much a torque converter multiplies torque, and B) the other big question mark of how much torque I'll actually be making. I won't be crawling over a rock at WOT, so how does one factor in all those unknown variables?
I guess I'm asking... how would an automotive engineer choose components. They put a 7.2" in the AWD vans, but an 8.5" in the 4x4 trucks with the same basic layout. Did they do that because the trucks actually need the capacity, or is it just because they've always done it and it was the easy button?
Curtis73 (Forum Supporter) said:
350 torques * 3.06 first gear * 2.78 xfer case low range = 2935 torques on paper.
Divided that by two since it is a 50/50 torque split = 1467 torques.
Incorrect assumption. A "true" 4wd transfer case does not have 50/50 torque split. It does on flat ground, with no steering input, and equal rolling radius on the tires at all four corners. Any deviation from that and the "torque split" is infinitely variable, even beyond 100/0.
Think about it. If you have a rear tire off the ground, the front axle is going to get 100% torque. If you are going around a corner and dragging an axle, one end is going to be applying torque to the driveshaft and not vice-versa, and the other end is going to be getting 100% engine torque PLUS the torque from the other axle. This is why axles might handle an 8 second pass just fine but snap when turning around for the return road, when a spool is used.
If you want a 50/50 torque split, put an open diff in the transfer case.
It is also fair to assume that you will never be full throttle in first in low range, especially not in the meat of the torque curve. Rock crawlers crawl at idle to just a little over. As long as you are using low range for control rather than pulling stumps you should be fine. Think of the expected duty cycle that a work truck would see with 4wd and compare to your expected use. If you are going to use it like a 4wd work truck, then upgrade.
The far more important point is, are you an idiot? Do you intend to stand on it and continue to do so when it starts to wheel hop? Neutral drops at redline for extra cool 4 wheel burnouts?
Or are you an adult with some mechanical sympathy?
I totally thought the thread title was going to have been a voice to text fail variation on, Meths, when catalytic converters are stolen, they're involved.
No Time
SuperDork
10/30/21 9:38 p.m.
As a generalization, it looks like worst case for calculation purposes would be 2.5:1 for multiplication when the difference between input and output is the greatest (stopped and engine at stall speed).
Once you start moving the torque multiplication decreases as output speed approaches input speed eventually getting to 1:1 multiplication.
Honsch
Reader
10/30/21 10:08 p.m.
I wouldn't worry about it.
The tires will slip long before the input torque is reached unless you have bad shock loading but since it's an autotragic you should be fine.
Pete. (l33t FS) said:
Curtis73 (Forum Supporter) said:
350 torques * 3.06 first gear * 2.78 xfer case low range = 2935 torques on paper.
Divided that by two since it is a 50/50 torque split = 1467 torques.
Incorrect assumption. A "true" 4wd transfer case does not have 50/50 torque split. It does on flat ground, with no steering input, and equal rolling radius on the tires at all four corners. Any deviation from that and the "torque split" is infinitely variable, even beyond 100/0.
Think about it. If you have a rear tire off the ground, the front axle is going to get 100% torque. If you are going around a corner and dragging an axle, one end is going to be applying torque to the driveshaft and not vice-versa, and the other end is going to be getting 100% engine torque PLUS the torque from the other axle. This is why axles might handle an 8 second pass just fine but snap when turning around for the return road, when a spool is used.
If you want a 50/50 torque split, put an open diff in the transfer case.
Problem is, with an open diff it's not 4wd, and the torque split is the opposite. With an open diff in the xfer case if I have zero traction at the back, (wheels in the air) the fronts get zero torque because the back wheels just spin.
What I really want is an NP247 with a viscous AWD, but that isn't happening from my initial research. Right now I have full time viscous. The NP247 has 2wd, open AWD, locked 4wd, and neutral. I'm giving up the viscous but gaining one step wimpier and one step traction-ier. Basically I'd be getting everything from full 4wd down to 2wd with an AWD in between as opposed to just one choice of viscous coupling AWD. I'm thinking that if the NP's open AWD presents trouble in the snow/mud, I'm one yank of a stick away from temporarily engaging 4wd. Right now I get viscous. I have a feeling that with the NP247 I'll just be shifting back and forth between open AWD and 4WD in conditions that require it.
There are thousands of combinations here. I have an LSD in the rear, front is obviously open. But the xfer case can be open or viscous (AWD), or locking (4wd) depending on which one you choose. My current configuration is actually quite capable with the AWD. My concerns are two-fold. 1) the BW case in there currently is a known weak point, and 2) I'm planning some overlanding and a mild lift. Having the option of locking the two axles together is a nice comfort when you're 10 miles from civilization.
There is also the added bonus that a stick on the floor and 4x4 decals on the side seems to instantly add $10k to its value.
Streetwiseguy said:
The far more important point is, are you an idiot? Do you intend to stand on it and continue to do so when it starts to wheel hop? Neutral drops at redline for extra cool 4 wheel burnouts?
Or are you an adult with some mechanical sympathy?
I am, but will other drivers/future owners have the same sympathy?
Plus 10k indeed! It's actually like 20k from what I've seen. It's crazy! The Quigly Ford Econolines are insanely expensive.
CyberEric said:
Plus 10k indeed! It's actually like 20k from what I've seen. It's crazy! The Quigly Ford Econolines are insanely expensive.
And a solid front axle with about 2" of suspension travel. They're awful. I always wanted one until I drove one. Punishing.
Curtis73 (Forum Supporter) said:
Streetwiseguy said:
The far more important point is, are you an idiot? Do you intend to stand on it and continue to do so when it starts to wheel hop? Neutral drops at redline for extra cool 4 wheel burnouts?
Or are you an adult with some mechanical sympathy?
I am, but will other drivers/future owners have the same sympathy?
Why would you care about that? You could build it out of depleted uranium, tungsten and kryptonite, and some bonehead would break it.
In reply to Streetwiseguy :
I'm a firm believer in doing something right or not doing it at all. Right now I have a functioning AWD van. If I make it 4wd without paying attention to engineering shortcomings, it does me no good to have a broken 4wd van... or a van that I can't use to its full potential because I'm worried something will break. For a challenge build I'll use duct tape and zip ties. For a functioning daily driver/adventure vehicle, it needs to be right.
How ticked would you be if you bought a drag-prepped Camaro that was ready for the strip and its first pass the rear end explodes because the seller's idea of race-prep didn't include upgrading from the glass 7.625" rear? Of course, you would have recognized it before handing over the cash, but 90% of buyers won't. I don't want to potentially kick the can down the road.
Put it this way: If I sell it someday, I'll have two kinds of buyers. 1) the kind that notices the 7.2" and runs away, or 2) the kind that doesn't, promptly takes it off-roading and breaks something, and then decides to be a shiny happy person to me about it.
Hence why I'm trying to determine if the 7.2" is adequate.
How easy would it be to upgrade the 7.2 later? Or would it involve re-replacing things?
If it's easy, I'd be inclined to keep it for now, get the thing sorted the rest of the way, then start using it. See if you start excessively wearing or breaking parts, then decide if it's adequate.
In the off road world, you see things like guys who insist a Dana 30 will break stuff constantly on 33s, then other guys who can wheel them on 37s and break nothing. So intended usage and your driving style can make a huge difference in whether a part is adequate. And just because you theoretically could break it with the available power, etc. doesn't mean you could realistically apply that much power to it.
rslifkin said:
How easy would it be to upgrade the 7.2 later? Or would it involve re-replacing things?
From what I'm discovering, not easy at all.
The 8.5" used in trucks is a whole different critter. My first thought about going 4WD was the ability to add a disengagement for the front axles. No point in having 2wd, really unless you can disengage the drag and friction from the front axle. Looking to the trucks, there is no easy solution. I thought I could maybe take a truck 8.5 and put my axle tubes in it, but not only is the 8.5 casting wider, it uses different size tubes and different axle flanges. I thought about just cutting and pasting the whole truck unit in and making some custom axles, but something about the suspension geometry would make the arc of the axle be way off in the vans.
More research is underway, but it doesn't look good for an easy swap to anything
2 things to consider (I think they have been mentioned before so far).
1. A locking transfer case makes 100% of torque available to each driveshaft (imagine one end in the air - you'd still get full engine torque to the end on the ground). This is double the maximum you get with an open diff.
2. Torque requires resistance, ie the tires become the fuse. If you have an open front diff, 100% torque on the front axle is not generally a big deal because your resistance is limited to the max torque applied by the wheel with less grip.
This is why front axle lockers on things with a locking center diff break things. With the front diff locked, max torque to all the front stuff (driveshaft, diff, both axles, hubs, etc) is instantly doubled.
I'd say you'll be fine if you leave the front diff open.
Robbie (Forum Supporter) said:
2 things to consider (I think they have been mentioned before so far).
1. A locking transfer case makes 100% of torque available to each driveshaft (imagine one end in the air - you'd still get full engine torque to the end on the ground). This is double the maximum you get with an open diff.
2. Torque requires resistance, ie the tires become the fuse. If you have an open front diff, 100% torque on the front axle is not generally a big deal because your resistance is limited to the max torque applied by the wheel with less grip.
This is why front axle lockers on things with a locking center diff break things. With the front diff locked, max torque to all the front stuff (driveshaft, diff, both axles, hubs, etc) is instantly doubled.
I'd say you'll be fine if you leave the front diff open.
On the other side of the coin, with a smooth driving style, lockers can also save parts. If you have an open diff, it's easy to get a momentary spin and grab on one wheel, which gives a nasty shock load. With a locker, the spin doesn't happen. And shock loads break things faster than anything else.
So if you drive off-road without the lead foot, avoid wheel hop and don't let a wheel spin and then suddenly grab traction, a lot less parts get broken.
I can drive without a lead foot. Most of the places I off-road will be fine with 4hi, I just don't want to be turning on some dirt and get more traction than anticipated and snap something.
My 4 wheeling is mostly trails in the woods on the way to camp, fording streams, and being able to move in deep snow for work emergencies and the like. What I'm planning is to get into overlanding with some camper-van groups and I don't want to be "that guy" who doesn't bring adequate equipment and I inconvenience everyone.... or James May when he breaks something while Hammond and Clarkson journey on leaving me to die a slow painful death.
So the question still remains... how much torque does a torque converter amplify? I've heard everything from "none" to "3-4 times" all the way up to "8 times."
In reply to rslifkin :
I was causing a lot of drivetrain issues because of a locker. Smooth they are definitely not.
Well, I'll be sticking with the LSD in the back and an open front. I highly doubt I'll need more than that, but if I do there are lots of things I can do without going crazy. Eaton style rear with applicable springs, Air locker rear, souped-up gov-lock, Torsen front, air locker front... but I don't think I need any of that.
Put it this way... if I need THAT much traction, it means I'm likely crawling over things that would cause rollover before I get stuck.
There are diffs available for the front?
