Our track time uncovered the fact that the older (and likely worn out) Bilstein PSS9 coilover system was too softly sprung and too weakly damped for our kind of serious track use; note that this setup is more of a street performance upgrade. Also, the existing OEM factory suspension, rubber bushings and so on allowed for far too much suspension movement in toe/caster changes. This well-used suspension combination caused imprecise handling nuances and destructive tire wear (all four tires needed to be replaced after just a few track outings). In addition, a major issue with the 996TT AWD system is the lack of a limited-slip differential (LSD) in the rear; the system is fairly unsophisticated in that the viscous coupling simply transfers power to the front wheels when there’s a difference in wheel speed from front to rear (up to 30 percent of the max power can be transferred to the front). This works nicely on the street, but at the track when accelerating out of corners, the car will push like a pig when the inner rear wheel loses traction and power transfers to the front wheels. We also tried our 996TT in RWD mode (a la GT2), by simply removing the center driveshaft (about 30 minutes of work underneath the car), as this modification is highly touted for track use in some online forums. However, without a rear LSD, this resulted in drastically slower lap times due to inner wheel spin on corner exits. But on the other hand, it did allow for some seriously cool drift action. Regardless of RWD or AWD preference, we believe there will be marked improvement in handling with the addition of a rear LSD.

In the next series article, we will install a new aftermarket LSD, pick up a new set of tires, and collect an official baseline lap time at the test track using our Traqmate GPS data acquisition system. Our budget supercar will then be ready for future tweaks and refreshing of its already-excellent brake system, a full suspension makeover, and numerous other go-fast additions… and deletions.

By Doug Neilson
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