Haldex rear LSD

[RudyH]

yeah, but I need to figure out how much torque it's actually sending. There's limits to the stock clutches and blow-off valve.

I know the R diff isn't as beefie as the RS3 / TTRS. I can say right now, my rear haldex is doing perfectly fine at Stage II+, and if it weren't for the new 8Y.5 RS3 wait for Canada I would go Vortex Standard without batting an eye.

the thing is though, if a majority of the power is going through the front and there is a hard limit (by the factory) to the amount of torque (not a percentage) goes to the rear, the rear LSD won't be really useful.

When I got the Haldex tune, it made a massive difference on launches, but I still find the front Wavetrac LSD has been the best thing I bought especially for coming out of a corner. Since the front will ALWAYS have more power than the rear (you will never obtain a 49/51 or greater split). I still have a hard time justifying the money on a rear LSD.

 

[gingercabrio]

I know the R diff isn't as beefie as the RS3 / TTRS. I can say right now, my rear haldex is doing perfectly fine at Stage II+, and if it weren't for the new 8Y.5 RS3 wait for Canada I would go Vortex Standard without batting an eye.

the thing is though, if a majority of the power is going through the front and there is a hard limit (by the factory) to the amount of torque (not a percentage) goes to the rear, the rear LSD won't be really useful.

When I got the Haldex tune, it made a massive difference on launches, but I still find the front Wavetrac LSD has been the best thing I bought especially for coming out of a corner. Since the front will ALWAYS have more power than the rear (you will never obtain a 49/51 or greater split). I still have a hard time justifying the money on a rear LSD.

The SSP for the Gen IV (Mk6 R, 8J TT) Haldex gives a maximum transmittable torque of 2400 Nm through the coupling. If we assume the bevel box step up gearing is the same factor of 1.6 with the Mk7, then you can transfer
(2400/(3.76*4.24))*1.6=241 Nm of engine torque through the coupling in first gear with the Mk7's 6MT. For the Gen IV coupling, you need to be making more than 482 Nm (355 ft-lbs) at the crank to still be front biased in first gear with the clutch fully locked up, if we ignore weight transfer during acceleration. The maximum transmittable torque for the Mk7 is likely much more, because the Gen IV Haldex runs at 30 bar, and I seem to recall the Gen V Haldex relief valve doesn't open until 44 bar.

I suspect a rear LSD in a stage 2 Mk7 R will always put more power to the ground than a front LSD in the same due to weight transfer, even in first gear.

 

[MeltedSolid]

I know the R diff isn't as beefie as the RS3 / TTRS. I can say right now, my rear haldex is doing perfectly fine at Stage II+, and if it weren't for the new 8Y.5 RS3 wait for Canada I would go Vortex Standard without batting an eye.

the thing is though, if a majority of the power is going through the front and there is a hard limit (by the factory) to the amount of torque (not a percentage) goes to the rear, the rear LSD won't be really useful.

When I got the Haldex tune, it made a massive difference on launches, but I still find the front Wavetrac LSD has been the best thing I bought especially for coming out of a corner. Since the front will ALWAYS have more power than the rear (you will never obtain a 49/51 or greater split). I still have a hard time justifying the money on a rear LSD.

The haldex clutch pack is essentially a center locker designed to be able to slip sometimes. As long as the torque being transferred is less than the threshold that the unit can handle, the haldex is capable of sending 100% of the torque to the rear (in reality it's just symmetrically locked below that threshold). I don't think thinking about torque split is very useful, it's just marketing's way of oversimplifying the system to the point of inaccuracy.

The advantage the LSD gives is in how that torque is used mid-corner, our fwd based cars will lift or nearly lift the inner rear tire in hard cornering, and if you're trying to put power to the rear during that, the open rear diff is just going to spin the inside tire essentially preventing any useful torque from being sent to the rear. I think this is one of the main reasons the mk7 R still handles more or less like a fwd car, and this is why the mk8 R's magna is so much better than the haldex, because it doesn't need to worry about that. The LSD isn't quite as good as the magna, but it helps to solve the same issue of being able to send power to the rear outside wheel when the inside wheel is unloaded. tl,dr rear lsd = potential for on power sideways and less on power understeer.

 

[RudyH]

but we don't have a trick electronic transfer case like say the EVO's do, so we will never get 100% to the rear unless the front wheels are on ice.
The front wheels will always be spinning and even if the Haldex locks up 100%, 50/50 since the the front tires are attached always.

I don't think the MK8 / 8Y RS3 has this technology neither

 

[MeltedSolid]

but we don't have a trick electronic transfer case like say the EVO's do.

Actually this in effect is exactly what the haldex is, the bit we are missing compared to EVO's/Subarus is a center differential, so it won't split the power without an active input. "50/50" is only accurate in an open differential system, and it never truly applies to a haldex style system. The EVO's system will also never send 100% to the rear unless the front wheels are on ice.

 

[scrllock]

but we don't have a trick electronic transfer case like say the EVO's do, so we will never get 100% to the rear unless the front wheels are on ice.
The front wheels will always be spinning and even if the Haldex locks up 100%, 50/50 since the the front tires are attached always.

I don't think the MK8 / 8Y RS3 has this technology neither

We have a similar system to the Evo X in that both are transverse layouts with an electronically controlled "center diff". Difference is that the evo x has S-AWS controlling a clutch pack in the transfer case (equivalent to bevel box) and we have 4motion controlling a clutch pack at the input shaft to the rear diff. The Evo X also has AYC, which functions similarly to the Mk8/8Y rear e-diff, tho AYC involves a failure prone hydraulic pump for side-to-side rear torque spltting.

The GTR/STI have a longitudinal setup which allows for more rear bias just like "true" quattro on longitudinal audis.

With mechanical LSDs front and rear we basically have the Evo 8/9 setup, albeit with electronic control of the center "diff."

 

[gboticus]

As an aside, got a real fuzzy response from wavetrac when I asked them about the LSD's. Basically that they've been promised an engineering sample, and if they don't need revisions will start shipping them. Stopped short of giving any timelines.

 

[scrllock]

so the same story as last september

 

[gboticus]

so the same story as last september

Yep.

 

[RudyH]

We have a similar system to the Evo X in that both are transverse layouts with an electronically controlled "center diff". Difference is that the evo x has S-AWS controlling a clutch pack in the transfer case (equivalent to bevel box) and we have 4motion controlling a clutch pack at the input shaft to the rear diff. The Evo X also has AYC, which functions similarly to the Mk8/8Y rear e-diff, tho AYC involves a failure prone hydraulic pump for side-to-side rear torque spltting.

The GTR/STI have a longitudinal setup which allows for more rear bias just like "true" quattro on longitudinal audis.

With mechanical LSDs front and rear we basically have the Evo 8/9 setup, albeit with electronic control of the center "diff."

it's similar but not the same....

http://youwheel.com/home/2017/04/15/analysis-awd-system-of-the-mitsubishi-lancer-evolution-x/
The clutch pack in the transfer case is the magic which we don't have where the front wheels get to slip out. Yes otherwise the center diff is quite similar...
but never think we can get 0% FWD and 100% RWD in the Golf R only unless you are in marketing.

Yes with the center diff we can do 100% FWD and 0% RWD.

 

[MeltedSolid]

it's similar but not the same....

http://youwheel.com/home/2017/04/15/analysis-awd-system-of-the-mitsubishi-lancer-evolution-x/
The clutch pack in the transfer case is the magic which we don't have where the front wheels get to slip out. Yes otherwise the center diff is quite similar...
but never think we can get 0% FWD and 100% RWD in the Golf R only unless you are in marketing.

Yes with the center diff we can do 100% FWD and 0% RWD.

We don't... have a center diff... That's the whole thing we're missing.

You have a decent understanding of how the EVO's system works, but you should do some research on how the golf's system works. It's not as good as the EVO's system, true, but you are comparing them in an inaccurate way.

Like I said, the % front vs rear isn't a very accurate way of describing the system. Both the EVO and the Golf can lock the front and rear axles together, the difference is the EVO has a differential, so it's still AWD even when it's clutches aren't engaged, where as the Golf is only FWD without the clutches engaged (making the Golf technically 4WD, not AWD, but that's a whole other can of worms).

 

[MeltedSolid]

As an aside, got a real fuzzy response from wavetrac when I asked them about the LSD's. Basically that they've been promised an engineering sample, and if they don't need revisions will start shipping them. Stopped short of giving any timelines.

To give a small update, I emailed Wavetrac today asking about a few other things and also mentioning the rear LSD. They told me "The Mk7 rear diff is a new application that is still in production and should be available likely sometime in late March or so".

 

[gboticus]

To give a small update, I emailed Wavetrac today asking about a few other things and also mentioning the rear LSD. They told me "The Mk7 rear diff is a new application that is still in production and should be available likely sometime in late March or so".

So still possible to get done while my engine swap is happening, great. Though both are still likely to slip another quarter two at this rate

 

[scrllock]

 

[gboticus]

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