It's been a while since we last visited our Project 996TT (EC 6/12) but since then, the worn brake rotors on our bargain basement used '01 Porsche Turbo have become a bigger concern. During our baseline runs, there was a question of safety when running flat-out, so this is where we'll start.
With the hydraulic system in good shape, all that needed attention was the rotors and pads. We also planned a fluid change and inspection of the lines as a matter of course since we're unaware of the car's history.
The solution was simple: Larger GiroDisc two-piece rotors all-round and high-performance track pads. The slotted rotors measure 350x34mm front and 350x28mm rear (OEM rotors are 330mm), retailing at $2400.
The two-piece rotors save about 2 lb front and 2.5 lb rear. And with the larger diameter rotors, longer caliper bolts and spacers were included in the kit to space the factory calipers.
For our track use, slotted rotors were chosen because we felt they were less inclined to crack under the intense heat like some drilled rotors.
We selected Endless ME20 performance pads that seem to work surprisingly well on the street. The system was flushed with Endless RF650 Racing Super Fluid (EC 11/11).
While we were at it we upgraded the brake ducts. Our research indicated the 996 Twin Turbo can be fitted with 997 GT3 ducts front and rear for improved cooling. The changes were made at the track to allow us to measure temperature differences on the same day. Admittedly, this procedure was a pain, but the only way to gather such data.
Once the new brakes were bedded in, we ran some baseline laps. The 996TT was able to run consistent times of 87.5sec at our two-mile, 11-turn racetrack. Unfortunately, adding the GT3 cooling ducts didn't measurably reduce our times, but were found to reduce front/rear rotor temperatures by 45/65?C and caliper temperatures by 23/30?C, respectively, as measured by our pitlane pyrometer.
The reduced temps would definitely help on longer sessions over 20min, the additional cooling reducing fade from boiling fluid or pad de-gassing.
Pedal feel with the Girodisc rotors and Endless pads was firm with very good initial bite, inspiring plenty of confidence for the driver.
Larger 350mm grooved GiroDisc rotors come with longer caliper bolts and spacers
Endless race pads were found to be usable on the street
Endless brake fluid ensured the hydraulic system was fully replenished
Next in our quest for chassis perfection was suspension. With nearly every rubber bushing and major component past its prime, it was time to overhaul the suspension. This would include replacing the rear suspension links with Road Sport Supply units (retailing at $1075). At the same time, RSS Tarmac Series control arms would replace the front and rear arms ($1900), while a KW Clubsport coilover kit was also installed ($5499).
The excellent RSS hardware is an easy way to reduce the slack in the suspension (even if your bushings are new), resulting in a tighter, more adjustable set-up for track cars (including caster, roll center, and additional camber using supplied control arm shims).
The KW Clubsports were designed around linear race springs with stiffer damping and increased strength to absorb racetrack punishment. They're ideal for enthusiasts who regularly like to participate in track days or training courses.
The KWs are still compliant enough to deal with large bumps and poor pavement on the street, being adjustable for compression and rebound damping independently. What's more, the Clubsport valving can handle large compressions, such as running over high track curbing.
During the installation, we also took the time to replace sway bar and transmission mount bushings and after eight hours of suspension installation and a four-wheel alignment we returned to the track, raring to go.
We had decided to test the merits of running in AWD and RWD by simply removing the driveshaft fitted between the front diff and transmission. This RWD set-up, a la GT2, is touted as the way to get the most performance from the 996TT chassis.
Running first in stock AWD, the transformation from the new suspension was amazing. The firmer and tighter suspension was much better damped, drastically improving the ability to maintain the car on the edge of adhesion.
Braking stability and steering feedback were also sharpened, and the bump-induced wallow was gone, replaced with precise control and improved feel.
The car felt surefooted and neutral in both slow and fast corners, even with the non-adjustable OEM sway bars.
During our testing we found a significant amount of time using the high curbs without unsettling the 996TT, allowing us the run harder than ever before. Consistent lap times were reduced to a scintillating 82.9sec. This represented a significant reduction of 4.6sec per lap.
After removing the driveshaft to run in RWD mode, the laps were certainly more exciting and challenging; can you say "drift action"?
We were expecting this combination to result in faster lap times, but the car suffered traction problems out of corners, limiting the times. In this configuration the car didn't have the stability of the full AWD set-up and was considerably slower. In fact, the RWD times were 84.4sec - 1.5sec slower.
Part of the problem was that there were numerous corners where the throttle had to be modulated, whereas in AWD it would be flat to the floor. The limited-slip differential we installed in the rear transaxle in Part 2, when combined with front-wheel drive made our AWD machine really hook up, producing faster lap times. It just goes to prove once more that you shouldn't believe everything you read online!
Porsche 911 GT3 brake cooling ducts fit the 996TT and while they reduced rotor temps there was no improvement in lap times
KW Clubsport coilovers offer compression, rebound and height adjustment, allowing more control and stability on-track
Beautifully machined RSS lower control arms, rear links and camber adjustment shims