Can someone red pill me on the various nuances of All Wheel Drive systems between manufacturers?

All you need to know is that Audi quattro is the best system.

What are the Japs and Americans running? Haldex?

Haldex Gen 4+ can pre-lock the clutch based on throttle input

Not an unusual system. Porsche uses something comparable. However if traction is everything you want a center differential to apportion power instead. Systems like ATTESA will work for snow but you're not going to go off road with it.

Why won't it work offroad?

That's because it is.

Want to do skidz? Flip the switch and make it stay in RWD.

Want to put 1000hp down to all 4 wheels with the stock diffs and driveshafts?
Go for it

Subaru has true AWD in the sense that (most of) their longitudinal systems are 50/50 power split in terms of front to rear, and can shuffle that around a bit. Downside is that their boxer is in front of the front axle, which causes understeer.

BMW X-Drive is a similar system in most cases, although it's usually more rear-biased. Very little downsides, except weight, and it uses a seperete center diff iirc.

Volkwagen Haldex systems (branded 4Motion) are considered shit, because they're FWD until you slip, and even then cannot send more than 50% of the power to the rear wheels. This is completely opposite to Audi's true TorSen systems (branded Quattro in most cases, although they do have some Haldex stuff branded Quattro as well). This system allows for permanent AWD, with a variable power split, up to 25/75 and 75/25. Downside to the Audi system is that they usualyl design it with the engine's CoG in front of the front axle, again, causing understeer.

Read this: awdwiki.com/en/home/

Pretty sure mazda runs haldex for their awd models. Dunno about toyota and the others tho.

ATTESA is the best AWD system, hands down.

It works like this, grab a nice straight 6, now put a manual gearbox behind it. Now you have a center diff behind the gearbox with essentially a straight connection for the rear driveshaft which goes to an LSD in the back and drives the rear wheels.
I6, manual, RWD with an LSD. The car stays and behaves like this most of the time, pottering around town or WOT on a freeway for example.

But now it's raining and you're trying to put power down out of a corner, what do you do?
Well, the center diff sends power sideways a few inches, pic related, and powers another driveshaft up to the front of the car.
Because of the way the center diff works, it can send up to 50% of the power to the front wheels, making it a true AWD system. You can disable this manually on R32s by pulling a fuse or wiring in a switch, R33/34 are more complex but they all essentially work the same way, RWD until slip detected, start throwing power at the front until slip no longer detected or 50% reached.

Now there's a problem, though. You have a driveshaft coming up to the front of the car on 1 side, but you need to power both wheels or else it's a 3 wheel drive.
So this means you need to raise the engine to get the driveshaft under it, right?

Nope. What you do is you cut a fucking hole straight through the sump and jam the driveshaft through that, letting the engine still sit fairly low.

Now, you might be thinking to yourself 'hold on, this dickhead just described the same thing a patrol or landcruiser uses, it's just 4x4'.
And you'd be right. ATTESA AWD is essentially a 4x4 system but with automatic torque split meaning it can do variable torque front/back unlike a 4x4 system which locks everything at the same speed.

Daihatsu is Haldex-style iirc.
Honda and Toyota use Haldex-style AWD, as well as FWD ICE's combined with electric RWD to make AWD setups. The NSX is of course electric FWD+ICE RWD.
Mistubishi uses full-time RWD biased AWD on some offroaders, FWD-based Haldex-style on their shitboxes, and the Evo used RWD-biased, FWD-based AWD.
Nissan uses ATTESSA style RWD-biased AWD, and FWD-biased stuff on their crossovers.
Subaru has been discussed ITT before. Mainly longitudinal 50/50 AWD.

Pic related for the front diff+sump

Too bad that I6 is so long. If you just used a V6 like any sane person, that front diff would've been completely ahead of the sump.

Still, oen of the most superior AWD systems there is.

I've driven on snow for 6 months of the year all my life, and I have made up a pretty clear idea of whats gud and what isnt when it comes to AWD.

I love Audi, and will probably always stay with them. I also like VW, but there are a few things about AWD that cannot go unsaid. When it comes to 4motion and quattro with TorSen diff, theyre the best cars ive ever driven in terms of grip and power. A4's, A6's, A7's, A8's, passats < 05, theyre all great with the "real" quattro/4motion system.

Haldex isnt like "REALLY FUCKING BAD", but the fact that theyre FWD with AWD "when needed" is just not so great. It doesnt mean that its bad, because FWD is by far better than RWD when it comes to driving in slippery conditions. But those times when I've tried a haldex system in loads of snow and ice, it just shines through that this system is pretty weak. It kind of kills engine power, and the amount of time it takes the rear wheels to respond is too long from time to time.

TorSen diff AWD a best, Haldex not really a shit, but the whole FWD with AWD when needed stuff is pretty gay anyways.

Good luck spinning a V6 to 8,500rpm back in 1989 reliably enough for warranted sale and 600hp+ racing

Throwing a driveshaft through the sump works fine and lets you enjoy that delicious I6

>Good luck spinning a V6 to 8,500rpm back in 1989 reliably enough for warranted sale
The R32 (first sold in 1989) had an 8000RPM limit. The Z32 had a 7200RPM limit. Both produced 280hp in twinturbo form, warranty and all. RPM doesn't even amtter if you're making the same HP, and I don't think any manufacturer cares about HP after tuning.

>Delicious I6
Delicious understeed thanks to an extremely long engine, with the CoG in the wrong place, well over the front axle. Also, iron block, so even more weight in the wrong location.

>8000RPM limit
In factory road trim, in racing form they'd pull out to 8,500rpm.

The 300ZX also wasn't designed for racing like the 32, it didn't need stand up to the abuse that the RB was expected to.

RPM does matter because HP is torque x rev, more rev = more power and with 80s turbo tech a wider powerband.

Of course nissan cares about HP after tuning, the road cars had to be the same as the race versions, so the engine and drivetrain were built to take 500-600hp. Doing this reliably in the 80s and 90s meant you just couldn't do a V6, it's only now in the 00s that it's become viable, hence why the R35 is.

>Delicious understeed thanks to an extremely long engine
Length itself does nothing to handling
>CoG in the wrong place
Block is inline with the transmission and tunnel as in any other car, hence the cut out sump
>well over the front axle
Better than in front of it
>iron block, so even more weight in the wrong location
The absolute worst of the 32-34 GTRs were 55/45 before you factor in fuel and driver weight, this really isn't the end of the world. By the time you take a 33 vspec and put the battery in the boot you're talking 52/48 which means with the proper RWD with occasional AWD setup, essentially no understeer.

GTRs were always setup with slight oversteer tendencies and the 32 especially with it's slow updating computer for the front power was actually quite hektik

>The 300ZX also wasn't designed for racing
You've never heard of IMSA, have you?

>HP=torque*RPM
So with HP at 280 each, and the R32 making more RPM, it actually had less torque. Great.

>so the engine and drivetrain were built to take 500-600hp
See above. The IMSA V6's started out at 650hp, and by the end of their cycle were pumping out closer to 800.

>Length itself does nothing to handling
The longer an engine (in a front engined setup), given an idnetical firewall, the more weight it's going to put forward, and the more it'll tend to understeer. Understeer is abd for performance. Using your AWD system as a band aid for this problem isn't solving the problem.

>Block is inline with the transmission and tunnel as in any other car
So, given that same transmission position, it's CoG is about one an a half cilinder further forward compared to a V6. Pic related.

>Better than in front of it
Worse than behind it.

>52/48
So still ridiculously front heavy for a RWD-biased car. Most proper RWD racecars try and work towards a 40/60 distribution.

It lacks a proper locking differential for the front wheels in most cases. ATTESA also lacks a center differential contrary to what some people are saying. As a result in order to do anything between full 50/50 and 2/98 torque split you're going to be slipping clutches. If you're constantly in low traction instead of just occasionally skidding those clutches are going to get incredibly hot and fail if pushed too far.

If this sounds familiar, it's because the Focus RS has this exact same problem because in track conditions the car is constantly under steering and needs the rear wheels to kick in to correct it.

True 4WD cars are going to have three differentials that can be locked at will to minimize power loss and avoid heat generation from traction control schemes to deal with open differentials or slipping clutches to achieve a desired torque distribution.

ATTESA doesn't have a center diff. That's the reason why it's relatively efficient for road car use because you aren't constantly paying for the efficiency loss for AWD.

ATTESA has a transfercase with a wet multi plate clutch that determines how much power is sent to the front wheels. This is part of the transmission and is under the shifter for the R32-R34 GT-R and back under the rear seats for the R35 GT-R.

You can tell because there's no rear seat headroom in the R35 GT-R compared to the R32-R34 GT-R. Similarly, you can tell that the transmission tunnel is enormous on the R32-R34 GT-R because the floor pan is not flat like a traditional FWD or RWD car where the driver and passenger place their feet.

ATTESA is great for roadgoing vehicles that may see some snow but it's not going to be ideal for something like a Toyota Land Cruiser.

This is definitely not true either. I have books and actual wheel weights from SAU that all say that the R32 GT-R was 60/40. Nissan did a lot of heroics with the R33 with weight saving including relocating the battery to the trunk and making the car itself much longer than the R32 to drive the weight distribution to 55/45. For the R34 they still were dealing with an iron block I6 and were constrained by the need to reduce length and wheelbase so weight distribution remained at 55/45.

If you read some engineer interviews on the R34 GT-R in retrospect, they were disappointed that they could not make the car that they wanted. It was going to move to aluminum block at minimum, if not a V6 to try and truly resolve the weight distribution issues. The engine would also be pushed back to make it closer to a midship platform. Things like the brakes were also planned for upgrade but Nissan going near bankrupt in the late 90s meant they just used the R33's Brembos.

You can see a lot of these elements in the R35 for a reason. The weight distribution is 52/48.