From Nissan 350Z & 370Z Wiki
Intro
Since its inception over two years ago, the Nissan 350Z has gained
tremendous aftermarket support and with due cause. Unlike its
boosted older brother, the 300ZX, the 350Z was delivered to our
shores with a naturally aspirated 3.5L V6 engine. And despite
having an acceptable 276hp output, the allure of twin turbochargers
inhaling mass volumes of air and making explosive power has become
quite appealing to many350Zowners.
Many companies have addressed the need for forced induction and Z owners have a wide variety of choices out on the market. The gentlemen from the land down under, Air Power Systems of Australia (APS) have set the standard with Their 350Z Twin Turbo Kit. APS has long been a major player in the WRX circle and they have jumped into the 350Z world with the most comprehensive twin turbo kit on the market.
We here at Z1 Motorsports chose the APS kit because it addresses all of the problems with other 350Z turbo kits and it was specifically designed and manufactured around the Nissan 350Z. The turbos are internally-wastegated Garrett GTs, each capable of producing 400 horsepower.
The intercooler is a bar and plate design that specifically fits in conjunction with the front bumper support brace. The fuel system upgrade supplied by APS consists of an upgraded high flow fuel pump and custom fuel pressure regulator and is similar to that which many enthusiasts have had to piece together on their own when trying to increase the boost on other twin turbo kits. The exhaust manifolds are cast log style that will outlast tubular units and APS uses a custom tuned Uni-chip to handle the timing and air/fuel adjustments while leaving the stock ECU to handle the rest of the vehicle's functions. Finally, the APS system comes with exhaustive installation instructions and visual diagrams to ensure that the installer has all the needed information on hand for a clean worry-free install.
The APS kit is made to be installed with the motor in the car and is certainly a viable endeavor with the right tools, a clean well ventilated environment with a flat floor and quality jack stands. Given our full compliment of lifts, engine hoists and air tools, we strayed from these detailed instructions by removing the engine and transmission from the car. Having the VQ35 on an engine stand while it undergoes its turbo metamorphosis definitely gives you more room to work and saves a few knuckles in the process.
After removing the front bumper and its support brace, disconnecting the battery and draining the fluids, the core support and radiator are removed. The resulting gaping mouth allows easy removal of the soon-to-be-boosted VQ35. Before the engine and transmission can be removed the exhaust is disconnected at the catalytic converters, the steering shaft is carefully marked and disconnected and the main wiring harness is disconnected. Once the shift lever is disconnected from the transmission, the engine and transmission are ready to be lifted out of the car as a unit. After removing the transmission the engine is bolted securely to an engine stand and the transformation can begin.
AIR
APS uses two internally wastegated, water-cooled Garrett twin ball
bearing turbochargers to stuff 8.5 psi of boost into the VQ35at the
stock settings. However, APS claims these Garrett snails are
capable of 800 hp airflow capacity at 16 psi of boost pressure with
a fully built engine.
Of course, turbos are only as good as the plumbing they are attached to. Exhaust gases that feed each turbocharger must arrive at the turbine with the maximum amount of gas energy in order to ensure crisp response and power. The hot exhaust side of this kit includes high flowing and high temperature-resistant iron, cast exhaust manifolds and turbine outlets.
Keeping all that extra air cool before it hits the combustion chambers is critical to making power. APS has designed and manufactured a huge 25 x 9 x 3.5-inch core, custom configured, vertical flow, high efficiency bar and plate style intercooler. APS claims that the pressure drop is less than 1.0psi at 650 flywheel hp. At the same turbocharger flow conditions, the intercooler outlet temperature is less than 15°F higher than ambient at any vehicle speed over 50mph.
Routing all this air into the intercooler and then back to the turbos is a tricky proposition in an engine bay that was not designed with twin turbos in mind. However, APS pulls it off with efficiency and style. Flexible air ducting connects the intake filters to beautifully polished 304 stainless steel compressor inlet piping. These equal length mandrel bent pipes connect the compressor discharges to the twin intercooler inlets where the air is chilled before being routed to the throttle body by way of a custom-molded silicon hose. On the way the chilled air passes through the MAF sensor and any un-needed boost is vented through the included APS high-volume, dual vent blowoff valve.
Routing all the required piping necessitates removal of the stock radiator overflow canister. APS includes a trick stainless steel canister as replacement for the molded plastic stock unit. Heat shielding is critical in order to protect the other components in the engine bay from the heat generated by these turbos. APS includes moldable stainless steel heat shields that will keep the extra heat from damaging nearby components.
Once the turbos, exhaust manifolds and turbo piping are mounted to the engine it is ready to go back in the car with the transmission. The radiator, core support and steering shaft are buttoned back up and the massive FMIC is bolted into place. Once the turbo compressor piping is connected to the inlet side of the FMIC and the FMIC outlet joined to the intake piping with 3-inch silicone hose, the front bumper and bumper support brace can be re-installed. APS designed the FMIC to fit with the front bumper support brace, maintaining full OEM front impact protection features. Flexible ducting connects the two cold air intake filters to the turbo intake piping and the supplied brackets ensure that they maintain their intended location underneath the headlights. Finally, the stock transmission cooler is relocated to the front bumper support brace to make room for the passenger side intake.
FUEL
More air plus more fuel equals more power. In order to compensate
for massive amounts of extra air supplied by the twin Garrett
turbos, more fuel is required. After removing the upper and lower
intake plenum the stock injectors can be easily replaced with the
drop-in quad orifice directional pattern injectors supplied in the
APS Twin Turbo kit. These injectors flow 500 cc at 4.0 Bar (58 psi)
differential fuel pressure and each of these are capable of
sustaining 100 horsepower (flywheel) while maintaining a 12.0:1
airfuel ratio. That's enough fuel for 600 flywheel horsepower!
Differential pressure is the critical yardstick when discussing injectors in forced induction applications. As boost pressure increases inside the inlet manifold where the injectors are situated (lower half of the intake manifold the fuel rail pressure must also increase proportionally in order to maintain a constant pressure difference across the injector orifice. This is called a constant differential pressure fuel system. Less sophisticated fuel systems may not employ a constant differential pressure fuel supply. These are called constant fuel pressure systems and were only ever intended for naturally aspirated applications. APS supplies an advanced injector-wiring loom in the upgraded fuel system in order to avoid cutting and soldering of the original injector looms.
The stock fuel pump assembly is located behind the passenger seat and removed for slight modification. In order to ensure precise fuel pressure delivery at high horsepower levels, a 4.0 Bar fuel pressure regulator replaces the stock 3.5 Bar unit. A vacuum line is run from the engine bay to the APS fuel pressure regulator which is vacuum/pressure referenced to the engine's intake manifold. The regulator is then mounted on the outside of the stock fuel pump/sender unit – and housed in a custom high flow housing assembly. In this way, fuel pressure across each injector orifice is maintained at a constant level regardless of the turbocharger boost pressure level - a configuration found in the world's best turbocharged production engines. The restriction caused by the stock 3.5 Bar regulator is removed completely and a new custom replacement plug is included to facilitate this. The APS custom high flow regulator housing is safely bracketed on the top of the stock fuel pump/sending unit and therefore no cutting of the stock sheetmetal is required.
ENGINE MANAGEMENT
If left alone the stock ECU would not know what to do with all the
extra air and fuel available to it. In order to put the extra fuel
and air to use, APS enlisted Unichip of North America to handle
fuel and ignition timing. The Unichip piggyback module is a
solid-state computer about the size of an MP3 player that comes
pre-programmed with an 8.5 PSI map claimed to be good for 400+
rwhp. By including a plug-and play adaptor to the stock wiring
harness, the APS kit eliminates the need or splicing into the stock
harness associated with many piggy back engine management
solutions.
One item of interest is that the end user cannot tune the Unichip piggy back module and it can only be tuned by a certified Unichip tuner. While this may frustrate the hobby tuners out there, it is undoubtedly safer for the average enthusiast to seek the services of a trained professional tuner when attempting to adjust the fuel and timing maps.
APS 350ZTT DRIVING IMPRESSIONS
Wow. This is what I wanted the 350Z to be from Nissan, a linear
improvement on the Z32TT. With a 120 rwhp bump in power and a
122Ib-ft gain in torque, the already torquey VQ35 supplies power on
demand throughout the RPM band. At 3500 rpm there are 60lb-ft more
torque than stock and 100 more at 4000 RPM.
Unlike the Z32 there is little if any delay in throttle response or "turbo lag", the power is just there whenever you want it! The only downfall with all this new torque is that a heavy foot will produce gobs of wheel spin and smoky burnouts off the line. Even having Volk SF Challenges wrapped with super sticky 275/35YR19 Michelin Pilot Sport PS2s, wheel spin through first, second and into third requires nothing more than a 2500 rpm clutch dump.
From a roll the extra power kicks in quickly and the 350Z really stretches its legs without gasping for air like it did in stock form. I took the car to the drag strip and the APS TT kit paired with Mickey Thompson ET Street Drag Radials produced a 12.44 with bracket-winning consistency at the NOPIX-Box event in Alabama.
There's not much more to say about the APS Twin Turbo kit other than you have to experience the thrill ride yourself!
