The difference between the R34 GT-R Z-Tune and other R34 GT-Rs
By Joshua Ho
There were a lot of changes from the R32 to the R34. Some of the major changes were primarily in the areas of suspension, chassis, and aerodynamics. One of the variants that saw some serious changes even compared to what tuners were doing was the Z-Tune variant. While most people know that the Z-Tunes were based upon the R34 GT-R VSpec I/II, most probably don’t know that there was a Z-Tune 1 that was a development prototype leading up to the Z-Tune 2 that was sold to the public. It was a very different car, much harder in the sense that it actually didn’t have some of the luxury trimmings seen in the Z-Tune 2, had much more power (600 PS), and lacked airbags. The car also came with a built-in roll cage. You can see some of the photos in the video below.
The Z-Tune as we know it came with a 2.77L GT500 block, crankshaft, and conrods that were said to be balanced within a gram of each set to maximize the smoothness of the engine. Turbos were IHI units used in the Falken R34 GT-R for the 24 hours of Nurburgring at 1.5 bar to produce a peak of 500 horsepower. Instead of the stock cast pistons, forged pistons were used that retained the stock oil cooling channels (this reduces the likelihood of detonation but more oil is sucked out of the crankcase by the PCV system) that were similarly balanced within a gram of each other. A higher strength GT500 water pump as well as a larger radiator were installed, along with a GT500 oil pump and extra oil coolers. Those that know about the RB26 will know that the stock oil pump has a tendency to fail so things like this go a long way to ensuring reliability even if you track it lap after lap. To prevent oil from pooling in the head, an oil restrictor was installed in the head. To prevent oil starvation at the pickup due to cornering, a baffled oil pan was also installed. This isn’t as good as a dry sump system which can be retrofitted to an RB26, but it’s good enough for just about anything short of serious racing.
A larger intercooler was also installed to reduce intake air temperatures due to the higher flow and boost pressure of the ball bearing IHI turbos. The Nismo GT Plenum was also used to better equalize the flow of air to all cylinders as the stock cylinder delivers the most air to cylinder 6 which also causes some differential in turbo flow rates and RPM. In Nismo testing, they found that the exhaust gas temperature delta between the two turbos dropped by 18%. Power output increased by 1.8% on boost and fuel economy increased by 0.4% as well. It doesn’t seem like much, but these little changes are what add up over time to become a noticeable improvement.
The engine also received a GT500 exhaust manifold, enlarged turbo outlets, redesigned catalytic converters, and the Weldina NE-1 titanium catback exhaust system. If you watched the Best Motoring video above about this car you’ll probably know that it was a huge engineering challenge for Nismo to get the camshafts right as well as ECU tuning. Most tuners push quite rich when boost goes high to protect the engine, but this leads to massive afterburns as the unburned gasoline hits fresh air and explodes on contact. This kind of shock can destroy a catalytic converter. This car was being sold as emissions compliant, so such issues had to be overcome before they were sold. Large overlap on static camshafts also leads to quite a bit of unburned fuel going straight out to the exhaust so there’s balance to be had here. Duration was 244 degrees on both intake and exhaust with a cam lift of 9.25mm. The intake and exhaust lift is quite aggressive when considering the relatively short duration, which is probably due to emissions and the need to improve mid-range power. It is interesting to note here that the generally accepted maximum lift values for camshaft lift is right around 9.25mm before they contact the piston for the RB26 so Nismo was pushing the limits of cam lift here. Despite the relatively short duration it’s interesting to note that Dino Dalle Carbonare at Speedhunters mentioned that the engine response was a little flat below 5000 RPM which is probably a function of the larger turbos and a lack of something like HKS VCAM, which increases part load exhaust gas flow due to internal exhaust gas recirculation and higher volumetric efficiency.
In addition to these changes, new air inlet pipes were used in conjunction with a new airbox and snorkel that directly connected to the hood. The air inlet pipes were designed to fix the notorious turbo shuffle issue that comes with the stock twin turbo pipe with upgraded turbos and allow for more air to flow in general. The airbox was redesigned to improve flow while retaining OEM characteristics for filtration and laminar flow as the MAFs need a carefully designed intake to work well. To reduce intake air temperature and increase the airflow to the airbox, the carbon fiber hood directly fed the airbox through a redesigned air scoop and duct. It also goes without saying that upgraded injectors were used to keep up with the larger turbo and engine.
While engine builds are nice, what really set the Z-Tune apart from everything else was the stiffened chassis and improved aerodynamics. Spot weld reinforcements were done to the door frame, along with carbon fiber around the front strut towers, floorpan, front fender outriggers, and transmission tunnels. Rigidity of the floor pan reinforced by dry carbon was increased by 2.7 times. The inner trunk wall between the rear seats and trunk was removed and replaced with dry carbon fiber. Carbon fiber was also used in the front fenders, hood, and bumper cover, which reduced the amount of weight on the front half of the car. Through these measures, the increase in chassis rigidity for better handling and performance was achieved without the use of a roll cage, which would have been extremely dangerous without at least a 4 point harness, helmet, and HANS device to prevent whiplash and contact with the roll cage.
I mentioned earlier that aerodynamics was a critical part of what set the Z-Tune apart from other R34 GT-Rs, and the changes to the body work significantly increased downforce, likely going from a near zero lift where the front tires only see minor unloading with increased speed to a true negative lift characteristic that increases grip as speed increases. What sets even the fastest street cars apart from true race cars like F1 cars is ultimately downforce, so these changes really add up quite a bit.
The hood of the Z-Tune was vented towards the front where air would be pulled out of the engine bay. The fenders were also flared near the side view mirrors to draw additional air from the engine bay as well as the front brakes which further reduced the amount of air trapped in the car at high speeds to improve downforce and cooling. The front undertray was also redesigned to direct air towards the brakes and increase downforce as the design was no longer a simple flat plate like it is on the VSpec. It’s interesting to see how Nismo’s lessons learned in racing the R34 GT-R applied back to this car as the design of the parts in the Z-Tune for aero and cooling bear more than a passing resemblance to the actual R34 GT-R race cars. Nismo claims that the front diffuser alone resulted in a 2.2x increase in front downforce. To retain balance, a new rear spoiler with a Gurney flap was installed to also increase rear downforce and side/rear skirts were installed to reduce pressure leakage from the undercarriage.
The suspension was also retuned with an emphasis on track performance. This meant hugely stiff springs at 14 kg/mm with Sachs three way adjustable dampers. To give some idea of how stiff these springs are, the Ohlins Road and Track coilovers that Nismo now uses are 9 kg/mm on the front and 8 kg/mm on the rear while the stock VSpec 1 springs were 4 kg/mm on the front and 5 kg/mm on the rear. However, it’s important to note that ride quality is not a function of spring rate alone, as the damper has a significant impact on the characteristics of the suspension. The Z-Tune is definitely not a smooth street ride though, as its suspension was tuned primarily to perform on the track. Harder rubber was also used for bushings in the suspension to further increase rigidity.
If you know the differences between the R33 and R34 GT-R you’ll know that for the most part the brakes were not really upgraded between the two generations save for some differences in ABS and a larger rear rotor for later years of the R34. For the Z-Tune, new brakes were developed in partnership with Brembo. Larger diameter ventilated and slotted rotors were added along with new calipers and reprogrammed ABS to work correctly on R-compound tires allowed the car to stop at up to 1.6g. It’s interesting to note here that Nismo generally continues to prefer cast iron brakes for their cars as even the Clubman Race Spec uses the steel R35 brakes. I suspect this is a matter of practicality as street cars are said to be better off with cast iron rotors for better performance at low temperatures and speeds.
In the driveline, a new twin plate clutch was used to handle the additional torque without slip, and a front LSD was added to improve the performance and steering feel as the differential makes the steering get heavier as it approaches full lock due to the increased speed differential. The stock Getrag V160 was retained as options like a true sequential dogbox are difficult to drive and really only make sense in race applications where the half a second lost to using the clutch to shift is a big deal. A carbon fiber driveshaft was also fitted which weighed 7.26kg vs the stock 12.56kg of the stock rear driveshaft. Additional cooling was also fitted to the transmission and rear differential. The rear diffuser was removed, although it seems that some sources suggest that it could be retained. Weirdly enough, the stock final drive was retained but this may be due to the need to retain a low highway cruise RPM.
To round out the car, the ATTESA controller was remapped to engage the transfercase more aggressively to make the car handle with less power oversteer to compensate for the dramatically increased power output. The Z-Tune also received an improved interior. A Nismo gauge cluster was installed, as was a Nismo MFD with additional functionality. A new steering wheel was also wrapped in Alcantara. The door cards and seats were also upholstered with black leather and red Alcantara.
The result was a car that set a new production car lap record at Tsukuba for its time. Only 19 were built and today the car is generally valued over 500k USD. While time has passed it by in a number of regards, the attention to detail is impressive even today and is a testament to Nismo’s capabilities when focused into a singular concept.
