996 Turbo 4wd System

[nevetas]

Is power only put to the front wheels when traction is lost, or is some power always delivered.

Is it simular to the impreza awd system, or is the porsche more/less clever.

I assume the porker is probably more rear biased?

[verysideways]

Viscous coupling, so power is always delivered (though minor, i believe they quote 5%).

If the rears start to spin up, the gelatinous liquid in the viscous coupling solidifies and thus transmits more power to the fronts (i believe they quote up to 40%).

Not sure if this is the same or different to Scooby, sorry.

[verysideways]

Broadly similar in the open front diff and slippy rear, but not on power split through viscous.
911 very much rear biased on power as well as weight (how appropriate).

[nevetas]

ok so if i started going through snow, the porker would start feeding 40% power to the front.

Whereas if I was going round a dry brands hatch, it would be feeding 5% power to the front.

[verysideways]

nevetas said:

ok so if i started going through snow, the porker would start feeding 40% power to the front. Whereas if I was going round a dry brands hatch, it would be feeding 5% power to the front.

Right up until the point you start powersliding yes...

(not that i have ever tried to powerslide a 996tt, but my 993tt powerslides beautifully in the dry - tries to kill me in the wet though)

[rumplestiltskin]

As said, much more rear biased than the Scooby, under normal - ie full grip - driving conditions 95% Rear / 5% Front.

[nevetas]

Would this also mean then it probably looses much less power through the drive train?

I think the scooby 4wd systems zaps allot of the bhp.

[GravelBen]

The DCCD Scoobies (STi type R and RA) are normally a 64/36% (or 66/34, can't remember exactly) rear/front torque split with centre diff set to open, then infinitely adjustable (with a dial beside the handbrake) up to complete lockup, in which case the torque split varies naturally depending on grip, as both axles turn together. up to 100% of torque can be transferred through the axle with most grip (ie front on ice, back on tarmac means 100/0 split and all torque through rear wheels) or 50/50 if both axles have same grip. They also have a mechanical rear lsd and viscous front lsd (though some models may be open front diff I think)

hope this helps

[MattOz]

Nevetas,

It's essentially the same as a skyline GTR set up IIRC. I know my old R33 GTR was mostly rwd until it lost traction, then the needle swung and torque/drive was sent to the front wheels.

Cheers
Matt

[aceparts_com]

Talking from experience, I nearly got my TT stuck in the snow going up the same slope that my partners 1.2 clio flew up!

[nevetas]

that doesn't sound to good. My scooby was amazing in snow even or summer tyres.

My M3 was very tricky in snow, was hoping the TT would be better.

Suppose winter tyres would make it easier, but they sound very expensive.



>> Edited by nevetas on Friday 21st October 14:53

[spenny_b]

Ah, thought it was the same Nevetas as from ScoobNet! ...I was in the Black Type-R that Sat morning when there was a test for [cough]garage door openers[cough] ...not that I had anything to do with it, was just waiting for the curry house to open!

Incidentally, the pictures in the owners manual for Type-R's are hilarious!...they show a characature of a guy driving his Scoob, all wheels off the ground over a yump, with the explaination something like "the Driver Controlled Centre Differential adjustment must NOT be adjusted whilst all four wheels are off the ground" (yeah, like my name IS Bjorn Waldegard!)...but the diff lock can be changed at all other time "on-the-fly"....which is nice.

[Raven Flyer]

The Scooby adjustable centre diff works by a solenoid pushing a piston into the diff casing and pressurising the fluid. This restricts the amount that it can flow by heating it, so reducing its viscosity. The Scooby system was only there for homologation and has no real use on tarmac. On gravel it is incredible. Wind it off to boot the back out and back on to power through the bend. The later programmable ones do all this for you and make heroes out of anyone.

Although I've had Scooby ones apart, I have no idea how the 911 one works. The 911 system is quite a bit lighter than the Impreza one though and I suspect that the max 40% to the front means that lighter/smaller prop shaft, front diff and drive shafts could be used. The lesser amount of torque to the front also removes the needs for a front LSD. Steering has a life of its own with front LSDs, as Focus RS owners will tesify.

Best car I ever had for snow driving was a 2.9i Granada Scorpio. Tail out action everywhere and easy to balance on the throttle and power through bends. All of my Imprezas understeered too much for fun snow driving at low speeds, but driving to Corcheval for the millenium, on snow covered French motorways was one of the best drives I've ever had. 80+mph powerslides round motorway bends

I'd imagine the 911 4WD to be a lot of fun with the torque split that they have, but the width of the rear tyres and the weight at the back is going to make catching the slide very tricky on snow.

[superlightr]

my 996tt was very bad on snow. Awfull when other cars were zipping by.

maybe tyres too wide for their own good at least on the snow.