The JWT clutch and flywheel kit came complete with a throw-out bearing and an alignment tool. A sprung hub and marcel spring combine with a high-clamp load pressure plate-with a re-tooled fulcrum point for low pedal pressure.
The intercooler assembly consists of two big bar-and-plate, air-to-air heat exchangers sharing a common center plenum to direct air to the throttle body. Bar-and-plate intercoolers are excellent heat exchangers and have more thermal mass than lighter tube-and-fin charge coolers. They're more effective at low speeds, or on the street, where airflow across the core is limited because a beefier core design takes longer to heat up. The flip side is that it also takes longer to cool down.
To prevent turbo-damaging, throttle lift-induced compressor surge, a single Bosch-type compressor bypass valve is situated after the airflow meter to assure proper driveabilty when modulating the throttle on boost. On cars with a mass airflow meter, if gases are simply dumped overboard (in ricer blow-off valve style), air already metered will not be ingested by the engine. Since the engine thinks this previously measured air is going to be burned, its ECU injects fuel for it. However, that air got dumped, so the engine momentarily runs too rich. This can cause stalling and sputtering.
The JWT turbo kit uses this huge dual bar-and-plate, front-mount intercooler, routing air through these lightweight aluminum mandrel-bent pipes (with beading on each end to prevent hose connectors from popping off). The intercooler is essentially two front-mounts fed by each turbo through the end tanks at either side. The cooled, compressed air merges in the central tank and is sent to the single throttle body on the VQ35DE.
Engine Management
JWT turbo kits use a pre-programmed piggyback spark timing computer, larger 530cc/min injectors, a larger in-tank 255lph fuel pump and a 4:1 boost-dependent fuel pressure regulator. JWT designed them to use a rising-rate fuel pressure regulator to work with the stock return-less fuel system (instead of reprogramming the ECU) so off-boost engine management stays close to stock. This allows our car to run as clean as a stock Z for emissions reasons. On boost, the larger injectors and higher fuel pressure will ensure a sufficient supply of gas. Spark timing is retarded through the piggyback computer, but only under boost. This turbo kit has produced well over 500 wheel-hp, with 530cc/min injectors and less than 14psi of boost. We relish the idea of making so much power at such an under-stressed boost level.
For our application, we will have some custom tuning performed on our factory ECU by Clark Steppler at JWT, to optimize performance with our hardware package. According to JWT, the 530cc/min injectors should be good for up to 700 wheel-hp.
Steve Mitchell chains the engine up to the M-Workz forklift. Forklifts are better than cherry pickers for dropping engines in, especially when the entire nose and radiator support is modular and removable, like the Z.
Driveline
A new clutch had to be procured to handle the near-doubling of power. We didn't want a multi-disc design that would make everyday driving difficult, since the car spends most of its time on the street. But we also anticipate some track beating, so finding a clutch with the right balance of usability and durability was critical.
After much searching and debate, we chose one of JWT's less aggressive, smoother and more streetable heavy duty clutches. The JWT Stage Three unit can easily hold our anticipated 540lb-ft of torque and offers the driveability we were looking for. We'll see what happens when we use the 700 wheel-hp the turbos and engine are capable of. At 500 wheel-hp and on super-sticky street tires, though, Project Z will already be traction-challenged .
The Stage Three clutch has a pressure plate with 2750 pounds of clamping force. Compared to the stock 1936 pounds, that's an increase of 70 percent. By fiddling with the fulcrum point of the pressure plate's diaphragm spring, this increase in clamping load comes with only a minimal increase in pedal pressure. The clutch disc uses heat-resistant metallic pucks for maximum holding power at high temperatures.
Since metallic pucks tend to have harsh, lightswitch-like engagement qualities and tend to chatter as the clutch is engaged, a four-sprung hub is used to make it more user-friendly. Marcel springs are leaf spring-like devices that look like Ruffles potato chips. As the clutch is engaged and the pucks come into contact with the flywheel and the pressure plate's pressure ring, the marcel spring limits the clutch's clamping force. As the clutch pedal is released further, the marcel flattens out and the full clamping load of the pressure plate can now bear on the puck, making for a smoother engagement.