Running a 1/2 mile airstrip event Sunday. Contemplating going RWD for the event to pick up a few more MPH. My car has and exhaust and tune on K16s and I'll be running 104 octane. I still have stock trans with open rear diff. What do you guys think?

 

AWD

Only because I know how slowly you work on your car. If you were to start the conversion today, you would be taking your S4 to the 1/2 mile event again.

 

Without a diff may as well stay awd

 

RWD should be faster so do that.

 

This is neither here or there, but I'd take the car in the setup which you usually drive it, that way you have an accurate idea of what it does in the real world.

Unless you've already been and know, then maybe try RWD to compare.. I dont think it is hard to just drop the front shaft, you could probably even do it at the event..

As 32Krazy said though, without a diff you'd be surprised how little traction you are going to have.

 

Drive it like it is (AWD?). Call it a baseline. No sure you'd see a measurably improvement. Try RWD next time. If you can get the car in the air, it's only a half hour or so to strip front driveshaft, if you feel so compelled. You will definitely have traction issues with stock diff and RWD, although mostly in 1st through 3rd...

 

LOL X!

RWD needs custom tuning to put the power down with less load. Leave it especially with just 16's

 

Ok, so I took the driveshaft off. Was super easy and quick. Going to test drive it this afternoon to assess traction situation and make a decision based on that. Car dead hooked on my PSS tires with AWD (used to spin a bit on a hard launch with PS2s)

 

:P It's already off

 

I am in the Bloomington area, you going to Rantoul? what does your car look like?

 

Yes. Polar Silver with gunmetal wheels and bright green calipers.

 

Well, I took her for a test drive in RWD mode. I don't notice any difference in straight line traction. I didn't launch the crap out of it but from a 5mph roll in first gear I got zero wheel spin in first or second gear.

 

The 996 Turbo AWD system can't be of much help from a dead stop launch or even a slow speed roll on. The viscous fluid coupling needs speed to get the fluid hot enough for it to transmit torque.

The amount of torque transmitted ranges from (official numbers) 5% to 40% with the 40% occurring at approx. 150mph.

On the web there are video clips of 996 Turbos and the driver is doing donuts on a snowy parking lot or snowy but otherwise empty street. While the rear wheels are spinning furiously the fronts aren't hardly turning at all. In fact the inside front wheel/tire is stationary.

 

Cool. I'll be there with my silver turbo. Gunmetal wheels and yellow calipers. Lol. I'll just be watching though.

 

This is wrong.

Our AWD actually is effective from a stop and low-speed situations, when in proper working condition. It also reacts in fractions of a second... It's weakness is in that sentence- the behavior is reactive rather than proactive (It can't take input from other systems and move power around appropriately) and it is a somewhat fragile system that has to be in proper working condition to do anything at all.. if the fluid in the coupling breaks down then it is essentially worthless.

Also, there is nothing to do with "fluid heating up" or speed in how our AWD works. Heat is the enemy. Heat is a by product of the friction that makes it work, but it is not the factor that makes it work. Viscous coupling fluid used in 996 is a thermally stable silicone based non-Newtonian shear thickening fluid. The harder a force is applied to one side of the VC and not the other, the thicker the fluid becomes and more connected it is front to rear, and it happens nearly instantaneously. Temperature stability is actually a key element in how these systems function because as heat increases viscosity slowly falls and less torque can be transmitted with hot fluid. The 5% minimum being transferred is due to the difference in tire height front to rear, it is a "pre-load" so to speak. The car may transfer 40% to front at 150 MPH, it's late and I don't feel like fact checking, but this would also be a function of a difference in tire height and fluid shear between F/R at speed rather than having to do with heat build up or speed of the car.

The videos that have cars barely able to or not able to move the front tires have failed AWD systems. In the 996, our VC fails due to the fluid Porsche used undergoing a chemical breakdown due to heat/age and the liquid in the coupling no longer having shear thickening properties... All it really takes is one good time to chemically compromise the VC fluid and it gets exponentially easier to cause even more damage every time until its worthless. If it the function of the system was a matter of building up heat, dont you think those cars sitting there spinning the rears without the fronts moving would eventually start moving the fronts as they sat there building up heat