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Old 04-07-2021, 11:41 AM #1
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Understanding V6's 4Hi mode, and V8's always-on 4Hi

The 4Runner is my first 4x4. I'm just trying to wrap my head around the various modes of 4x4, across the various models of the 4Runner.

From my research, as I understand it, the V6's 4Hi mode is EXACTLY the same as the always-on 4Hi of my V8. (Let me know if I'm off on that, or if there's any caveats).

I still have a question then, on what this 4Hi mode actually does, in terms of delivering effective power to each wheel, and comparing 4Hi + Center diff unlocked, vs 4Hi + Center diff locked.

With center diff unlocked, it seems to me that we still have open front & rear diffs, and power will still always go the wheel with the least traction.
  • So even if just one wheel is completely off the ground, it will get 100% of the power (to spin uselessly), and no power will be delivered to any of the other 3 wheels.
  • Is that an accurate assessment?
  • Is this is true, then what's the point of 4Hi with center diff unlocked?


With center diff locked, we get a 50/50 split of power to the front and rear axels. So if one wheel is off the ground, there's still 50% power at the other axel.

My last question is - when I'm driving on gravel or dirt roads, should I just lock the center diff right away? Is there any reason or benefit to NOT locking the center diff if I'm on a loose surface?
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Old 04-07-2021, 12:40 PM #2
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The center diff is a Torsen style limited slip differential, not fully open. When unlocked, it still acts as an LSD to direct power to the axle with the most grip.

-Rob
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Old 04-07-2021, 01:24 PM #3
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Quote:
Originally Posted by Iron Chef View Post
The 4Runner is my first 4x4. I'm just trying to wrap my head around the various modes of 4x4, across the various models of the 4Runner.

From my research, as I understand it, the V6's 4Hi mode is EXACTLY the same as the always-on 4Hi of my V8. (Let me know if I'm off on that, or if there's any caveats).

I still have a question then, on what this 4Hi mode actually does, in terms of delivering effective power to each wheel, and comparing 4Hi + Center diff unlocked, vs 4Hi + Center diff locked.

With center diff unlocked, it seems to me that we still have open front & rear diffs, and power will still always go the wheel with the least traction.
  • So even if just one wheel is completely off the ground, it will get 100% of the power (to spin uselessly), and no power will be delivered to any of the other 3 wheels.
  • Is that an accurate assessment?
  • Is this is true, then what's the point of 4Hi with center diff unlocked?


With center diff locked, we get a 50/50 split of power to the front and rear axels. So if one wheel is off the ground, there's still 50% power at the other axel.

My last question is - when I'm driving on gravel or dirt roads, should I just lock the center diff right away? Is there any reason or benefit to NOT locking the center diff if I'm on a loose surface?
You actually seem to have a pretty good grip of this. The Torsen center diff has a bias ratio, I think 4:1. So, if a wheel starts to slip, 4x the power can be sent to the opposite axle. However, when a wheel is in the air spinning, it effectively has 0 power (oversimplification) so 4 x 0 is still 0. ATRAC however is your friend, because it gives that spinning wheel some small amount of grip, which in turn allows the LSD to work its magic.

4Hi with center unlock is great for driving on roads with ice, or other variable grip situations. It will keep more grip longer than 2WD, but you can still turn. On trails, the advantage of center unlocked is corners. Sometimes, in tight turns on trails, you can end up with the front and rear wheels fighting eachother. This can increase your turning radius, which in some places is more a limiting factor than grip.

This is why the center lock/unlock is so handy. You can lock it when you need it, and leave it undone when you don't. That said, I end up driving with it locked mostly off road because it disables VSC. There is a mod to give "VSC off" its own switch, but I have not done that yet.
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Old 04-07-2021, 01:45 PM #4
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The point of 4H unlocked is to provide greater traction than 2H. You'll get 25% engine power to each wheel and they will be less likely to break traction initially. Also, you get to keep VSC, because that is disabled when the CDL is locked. I find 4H unlocked to be extremely useful, especially in winter conditions. On snowy roads RWD 2WD is not fun at all, haha. But 4H with ATRAC does a great job keeping me moving and VSC has saved me several time. The Torsen center LSD does a great job regulating the front to rear demands for the majority of offroading driving conditions I encounter.

As you become more familiar with your 4Runner, you'll learn what vehicle configuration works best for your needs. You might need the CDL more than I do if you're regularly lifting wheels.
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Old 04-07-2021, 01:45 PM #5
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Some helpful videos explaining the Toyota 4WD systems:

https://www.youtube.com/watch?v=pN6-gCxI60g

https://www.youtube.com/watch?v=4v2rC8sbkRM
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Old 04-07-2021, 01:59 PM #6
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Quote:
Originally Posted by Iron Chef View Post
My last question is - when I'm driving on gravel or dirt roads, should I just lock the center diff right away? Is there any reason or benefit to NOT locking the center diff if I'm on a loose surface?
When I'm offroad, I am constantly monitoring and judging my traction needs and making changes as needed. Most good condition, dry gravel roads don't even need 4H at all, so I will remain in 2H unless I feel the rear end getting squirelly or I can see an upcoming need for more traction. If I'm driving fast on gravel, 4H is my choice because it helps with steering response and I have more control. I rarely use the CDL for regular dirt/gravel roads. My AT tires keep enough traction to simply not need it. But if you've got shitty highway tires, you might feel the need for it.
Bottom line is, the driver needs to make the choice based on a multitude of variables. There really is no hard rule. (except no CDL on paved dry roads, lol)
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Old 04-07-2021, 02:50 PM #7
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Quote:
Originally Posted by RivMan View Post
The center diff is a Torsen style limited slip differential, not fully open. When unlocked, it still acts as an LSD to direct power to the axle with the most grip.

-Rob
Ahh, so the V6 is a fully open center diff then? (when unlocked)
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Old 04-07-2021, 02:58 PM #8
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Quote:
Originally Posted by Iron Chef View Post
Ahh, so the V6 is a fully open center diff then? (when unlocked)
No, the V6 is also an LSD center, just like the V8. The V6 just has the extra ability to be in 2wd.
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Old 04-07-2021, 03:04 PM #9
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Thanks everyone for your responses! Have a much clearer understanding of the subtleties of these modes now. So regarding CDL on or off, it depends on whether I need to prioritize turning response vs grip at any given moment.
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Old 04-07-2021, 11:23 PM #10
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I recall reading somewhere that the power ratio front to rear is 40F/60R due to the shape of the gears on the center torsen diff.

It'll behave a bit more like a RWD in most circumstances.
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Old 04-08-2021, 06:14 PM #11
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Quote:
Originally Posted by Keros View Post
I recall reading somewhere that the power ratio front to rear is 40F/60R due to the shape of the gears on the center torsen diff.

It'll behave a bit more like a RWD in most circumstances.
Yeah, that's also what I remember.
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