Thanks to the hard work of the transmission wizards at TRE we managed to start the 2002 ProSolo season off with a pair of Quaife Torsen limited-slip differentials in the centre and front positions, inside the transmission.

This was primarily done to replace the known to be fragile factory units, but it seems that it had another effect, that while it was not altogether unforseen, niether was it a given just from the theory.

A stock Talon/Eclipse has a viscous-style diff in the centre slot, and a conventional "open" differential in the front slot. The viscous coupling, while very effective at transferring power from one set of axles to the other, is a little slow to react, dependant as it is on the fluid inside the coupling unit heating up in order to provide locking force. This means that there is a time delay between an axle starting to slip, and the viscous sending power to the other end of the car to compensate.

With the open front diff, there is no mechanism to transfer power from one front wheel to the other. Furthermore, like all open diffs, once a wheel starts spinning, all the power is sent to the spinning wheel, not the wheel that still has grip.

So in a corner-exit situation, where power is being applied, if one of the front wheels were to break loose, all the power sent to the front axle would be diverted to the spinning wheel. And as there is a time delay at the centre viscous coupling before it starts locking and sending power to the rear wheels, that wheelspin is going to last for a little bit.

The end result seems to be the notorious "power-on understeer" that effectively limits how early and agressively you can get back on the throttle, especially in a powerful Talon/Eclipse. Paradoxically, a less powerful car can use more throttle leaving the corner, as it never makes enough power to threaten overpowering one of the front wheels and inducing understeer.

This is doubly painful in an AWD car, because the ability to jump back on the throttle early is the chief advantage of AWD over RWD or FWD. If you are not making use of that advantage, then you are hauling all that extra weight (of the AWD drivetrain) for nothing.

It seems, however, that fitting the Quaife diffs solved that problem. Certainly that was the impression from the driver's seat.

And now, thanks to datalogging, we can demonstrate it too.

This is a log of the turnaround at the 2002 Ft Myers ProSolo. The dark blue line is wheel speed. The red line is lateral G. The green line is throttle position, and the light blue line is brakes on/off. The horizontal black line is 0G lateral, and the vertical black line is the cursor, at which you can read the values of the various traces below the graph.

What the Lateral G trace shows is a turn with a sharp entry, a slightly flatter centre section, that then tightens up a little bit before opening up and then feeding (at the extreme right) into another turn in the opposite direction.

The interesting trace here is the throttle. Note no throttle under the brakes at corner entry. Mid-corner, there is some modulation, followed by a lift to get through the second, tighter apex. There is a quick stab to full throttle to see what the car will do, and when there is no push, the throttle is planted at 100% and held up to the entry of the follow-on turn.

Now, take a closer look at the lateral G trace in this full-throttle section. Notice that the car goes full throttle at the lateral G peak. Notice as well that lateral G falls off (which is consistant with unwinding the wheel) but then there is a little peak (at time 22.1) - this is a steering correction made at full throttle! In other words, the turn needed to be tightened somewhat, the wheel was turned, and the car responded with no throttle lift

Power-on push, successfully corrected, thanks to the Quaifes.