The maximum power split is listed as 80/20 rear biased on 993 TTs. Does this mean that sometimes the power split could be 40 or 50% to the front? What would be the maximum percentage available to the front? Under more or less normal driving and for that matter under spirited driving how much do you actually feel the front drive system?
The reason for the questions is that I am consdering purchasing a 993TT.
Thanks for any input,
Patrick
PS: Are there any particular problems I should look for in a 993TT? P.

 

Because the 993TT uses a viscous coupling (instead of traditional diff) between the front and rear differentials, power is transmitted to the front only when there is a difference in rotational speed between front and rear. In other words, when the rear wheels are spinning, the fluid in the VC heats up and power is transmitted to the front. More info: http://en.wikipedia.org/wiki/Viscous_coupling

In my experience, the rear wheels always begin spinning before power is transmitted to the front. In a cornering situation, this means power oversteer, so assuming you stay on a throttle (it's a 911, remember!), just as you dial in some opposite lock you can feel a little "pull" from the front end. Generally it handles like a rear engine, RWD car until you start to hang the tail out a little bit, and then you get some help from the front.

In a straight line, e.g. after an aggressive launch or in limited traction situations, the rear wheels light up and then the front wheels light up. I try to avoid this situation whenever possible because it often comes with axle tramp. I roll onto the throttle in first gear after the clutch is fully engaged, otherwise you beat the crap out of the drivetrain.

In street driving at stock horsepower levels I have to say the AWD system is pretty much transparent unless you're driving very aggressively.

At higher than stock horsepower levels, it becomes a little intrusive. On my car I dislike the effect of AWD on corner exit, because just as you start to rotate the car with power it sends some torque to the front and you have to adjust your line. It's manageable, but it doesn't feel smooth.

In short, it's not perfect, but as far as AWD systems go, I think this one is pretty well suited to sports car applications...

 

Hi Jeff:
Thank you very much for your indepth explanation of the handling characteristics of the 993TT. I have a 1987 Carrera 3.2 which I took to a track day last year and would likely do the same with the 993TT if I find an affordable one. Last year was the first time I had been on a track in thirty odd years, when I raced Formula Ford, and enjoyed myself thoroughly.
Patrick

 

Yes, the torque can vary between 5-15% depending on the slip of the rear drive wheels on a hard surface. It is depends on the torque transmitted to the rear where one could have 40% going to the front the front wheels if there is more grip in the front and the rears are spinning.
It is seemless in most driving situation unlike torque steer in front wheel drive cars, you hardly know its there.
You should read the wealth of information on this forum and find a good shop to perform the PPI.