The installation of a forced induction system on a Nissan 350Z or 370Z (often colloquially referred to as the "Z" platform, and sometimes "50Z" in enthusiast circles) is a major step toward unlocking significant horsepower gains. Both Stillen and APS (Auto Performance Systems) have long been respected names in the Z community, offering well-engineered turbo kits. However, even the best kits present real-world installation challenges that can turn an exciting weekend project into a weeks-long ordeal. Understanding these common issues before you begin is critical to planning a successful build. This article provides a deep dive into the fitment, electrical, cooling, and tuning hurdles associated with Stillen and APS turbo systems, along with actionable advice to avoid costly mistakes.

Overview of Stillen and APS Turbo Systems

Stillen's supercharger systems are more common, but they also offer turbo kits for the Z platform that balance daily drivability with power. Their kits typically feature cast manifolds, precision turbochargers, and comprehensive fuel system components. APS, on the other hand, is known for their twin-turbo setups designed for the VQ35HR and VQ37VHR engines. APS kits are revered for their ability to produce high horsepower numbers (800+ whp on built engines) but are also infamous for requiring meticulous installation attention.

Both manufacturers provide detailed instruction manuals, but the complexity of routing piping, securing oil lines, and integrating electronics means that even experienced mechanics will encounter headaches. Below, we break down the most frequent problems.

Pre-Installation Considerations

Before unbolting a single original equipment part, you must prepare. Skipping these steps is a primary reason installations go wrong.

  • Workspace and Tools: A clean, well-lit space with a vehicle lift or sturdy jack stands is essential. You will need metric sockets, wrenches, a torque wrench, a grinder with cutting wheels, a welder (for exhaust modifications), and a multimeter for electrical work.
  • Read the Manual Completely: Both Stillen and APS provide extensive instructions. Do not rely on memory or forum advice alone. Read the entire manual before starting, noting any steps that require special tools (e.g., flaring tools for oil lines).
  • Inventory All Parts: Open every box and compare contents against the included parts list. Missing bolts, gaskets, or hoses are a leading cause of stopped installations. Contact the manufacturer immediately if anything is missing.
  • Software and Tuning Access: Ensure you have a compatible ECU tuning solution—such as UpRev, ECUTek, or a standalone ECU—arranged in advance. A turbo kit will not run safely without proper tuning.

Common Fitment Issues

Fitment is where the majority of frustration lies. While Stillen and APS kits are designed for the Z chassis, the reality of mass production and variance between model years creates conflict.

Stillen-Specific Fitment Challenges

Stillen's turbo system for the 350Z (VQ35DE/HR) often requires trimming of the inner fender liner to accommodate the intake piping. The passenger-side turbo can sit very close to the frame rail, making access to bolts difficult. Many users report having to dent or massage the frame tab slightly to allow proper clearance, which is a normal part of installation. Additionally, the downpipe may contact the steering shaft on certain models, requiring either heat wrapping or a slight adjustment of the piping angle.

APS-Specific Fitment Challenges

APS twin-turbo kits are notorious for tight clearances. The turbochargers mount in a "low mount" position near the oil pan, which creates challenges with:

  • Piping routing: The cold-side pipes must snake between the engine block and the radiator support. In some 370Z installations, the piping interferes with the power steering cooler lines. A common workaround is to mount the power steering cooler in a different location.
  • Wastegate clearance: The wastegate actuators can contact the engine mount brackets. APS supplies spacer plates in newer kits, but older kits may require grinding a small amount of material from the bracket.
  • Intercooler placement: The front-mount intercooler (FMIC) supplied with APS kits is large. It may push the radiator back, requiring modification of the radiator fan shroud or using slim fans.

Electrical and Sensor Compatibility Issues

Modern turbo systems rely on correct electrical integration. Problems in this area can cause check engine lights, incorrect boost control, or even drivability issues.

Boost Controller Wiring

Both Stillen and APS include external wastegates that need a boost controller (electronic or manual). Wiring the boost controller solenoid incorrectly is a common mistake. The solenoid must be connected to a 12V source controlled by the ignition switch (not constant power) and to the ECU's boost control wire, if applicable. Using a multimeter to verify continuity is essential. Many installers skip this and later find the boost controller stuck open or closed.

Failed Fuel Pump Relay Connections

Turbo kits often require upgrading the fuel pump. If the pump is not wired to a relay triggered by the fuel pump prime signal from the ECU, the car may crank but not start. Some kits include a harness that plugs into the factory fuel pump connector, but if the connector is damaged or the wire gauge is too small, you may experience voltage drop leading to pump failure under load. Rewiring with a dedicated 30-amp relay and thick gauge wire is strongly recommended.

Sensor Relocation and Compatibility

On VQ35HR and VQ37VHR engines, the knock sensors and oil pressure sensor are located near the block. APS instructions often call for relocating these sensors to avoid interference with the turbocharger heat. Failure to properly insulate and secure the relocated sensors can lead to false knock readings and retarded timing, robbing horsepower. Use high-temperature silicone boots and zip ties to ensure they stay in place.

Exhaust System Modifications and Leak Prevention

One of the most critical parts of a turbo installation is the exhaust system. The Stillen and APS kits require welding of the downpipe to the existing cat-back exhaust or, in some cases, a custom midpipe.

Cutting and Welding Issues

The downpipe flanges may not perfectly align with the factory exhaust. A common workaround is to use a flexible exhaust section (flex pipe) between the downpipe and the cat-back to absorb movement and misalignment. Without this, cracking at welds is likely. Additionally, the O2 sensor bungs on the downpipe must be positioned so the wideband sensor does not hit the chassis or the steering shaft. If the bung is in the wrong location, have a muffler shop weld a new one.

Leaks from Poorly Sealed Joints

Turbo systems operate under significant pressure (10-15 psi typical). Any leak on the exhaust side will cause a boost leak, reducing performance and potentially damaging the turbo due to overspeed. Use high-quality gaskets (often supplied—do not reuse old ones) and apply anti-seize compound to studs to prevent galling. After installation, a smoke test or pressure test is invaluable for finding leaks before the engine is fired up.

Cooling System Integration: Intercooler and Heat Management

Heat is the enemy of boost. Proper integration of the intercooler and radiator is essential for consistent performance.

Insufficient Space for Intercooler

The Stillen kit uses a single intercooler mounted in the front bumper, while the APS twin-turbo kit uses dual intercoolers (one per turbo). On all Z models, space between the radiator and the front bumper support is limited. Many installers end up removing the active grille shutters (if equipped on 370Z) and trimming the lower bumper support. This is acceptable but must be done with care to avoid damaging structural integrity.

Hose Routing and Fitment

The silicone couplers and aluminum piping that connect the intercooler to the throttle body are sometimes cut to the wrong length. If the pipes are too long, they can rub against the radiator or the fan shroud, eventually wearing a hole and causing a boost leak. Use a hacksaw or cutoff wheel to shorten the pipes by 1/4 inch at a time, test fitting repeatedly. Also, ensure all clamps are of the t-bolt type, not worm-gear clamps, which can cut into silicone hoses under boost.

Oil Line Routing and Cooling

Turbochargers require an oil supply from the engine and a return line to the oil pan. The Stillen kit uses a sandwich adapter on the oil filter, while the APS kit taps into the oil pan directly. Common problems include:

  • Restrictor orifices: The oil supply line must have a restrictor to control flow. Using the wrong size restrictor can cause either oil starvation (too small) or oil burning (too large). Follow kit instructions precisely.
  • Return line slope: The oil return line must have a continuous downward slope to the pan. If the line dips, oil can pool and cause smoking. Many kits require modifying the pan with a welded return fitting. If not done professionally, leaks will occur.
  • Heat wrap: Oil lines near the exhaust should be heat-wrapped or have heat sleeves. Both Stillen and APS recommend this, but many novice installers skip it, leading to oil coking and turbo failure.

Tuning Requirements for Both Systems

You cannot simply bolt on a turbo kit and expect the car to run. Tuning is mandatory and often the most technically demanding step.

Finding a Compatible ECU Tune

Both Stillen and APS provide base maps for popular tuning platforms (UpRev for 350Z, ECUTek for 370Z). However, these base maps are generic. They will allow the engine to start and idle, but driving the car under load without a proper dyno tune risks detonation. Many owners make the mistake of using the base map for weeks while waiting for a tuner. This is dangerous—have a professional tune scheduled immediately.

Addressing Fuel Map Adjustments

Turbocharging requires significantly more fuel at high load. Even with upgraded fuel injectors (usually 650-750cc minimum), the fuel map must be carefully adjusted. Issues arise if the MAF sensor's scale is not rescaled for the larger intercooler piping. The Stillen kit uses the factory MAF housing, but the APS kit often requires a different MAF mounting location. If the MAF is too close to a bend in the piping, the readings become erratic, causing lean conditions. A true speed-density tune (using MAP sensors) eliminates this problem but is more complex.

Boost Control Issues

Setting boost levels requires careful calibration of the wastegate spring pressure and the boost controller settings. A common challenge with APS twin-turbo kits is that the two turbos may produce unequal boost if the wastegate actuators are not adjusted identically. This can cause knock and overheating on one bank. A boost controller with two channels (or a single controller with a split circuit) is strongly recommended. Do not rely on the wastegate springs alone—they can creep at higher RPM.

Oil and Fuel System Upgrades

A turbo kit that pushes more than 400 whp demands supporting mods. The stock fuel system in a 350Z or 370Z is only sufficient for modest boost levels.

Fuel Pump and Injector Capacity

Both Stillen and APS specify upgraded fuel pumps (Walbro 255 or 450 lph) and injectors. However, installation of a larger pump requires modifying the fuel bucket assembly in the tank. If the pump is not installed correctly, it can cause fuel starvation under half a tank. Use a proper install kit with a fuel-sock and hose clamps. For injectors, ensure you use the correct connector plugs—some aftermarket injectors require adapter harnesses.

Oil Supply and Return to Turbochargers

As mentioned, the oil supply system is critical. The Stillen kit uses a sandwich plate that sits between the oil filter and block. This plate can leak if not torqued to spec. Additionally, the oil filter may become very hot and degrade over time. A remote oil filter mount is a smart upgrade. The APS kit requires welding an oil return bung into the oil pan. This must be at a level where the oil can drain freely, above the normal oil level. If the bung is too low, oil will not drain properly, leading to smoking on deceleration.

Step-by-Step Tips for a Smooth Installation

Based on the common challenges above, here is a consolidated checklist to guide your installation process:

  1. Prepare the car: Remove all necessary components (front bumper, radiator fan, intake ducting). Drain oil and coolant. Disable the battery.
  2. Dry-fit everything: Before tightening any bolts, place the turbochargers, intercooler, and piping in position to verify alignment. This is the best time to spot interference.
  3. Address clearance issues early: If the turbo hits the frame, use a hammer to tap the metal tab. If the piping rubs, use a file or grinder to create clearance. Never force a component into place—it will lead to premature failure.
  4. Wiring harness management: Wrap all electrical connectors near the turbo with heat reflective tape. Secure the boost controller solenoid with a bracket away from heat sources. Use zip ties to keep wires clear of moving parts.
  5. Use thread locker and anti-seize: Apply anti-seize on all exhaust studs and flange bolts to facilitate future removal. Use thread locker (blue or red depending on torque) on turbo-to-manifold bolts to prevent loosening.
  6. Prime the oil system: Before starting the engine, crank the motor with the fuel pump fuse removed for 10 seconds to build oil pressure in the turbo lines. This prevents a dry start.
  7. Check for leaks twice: After first startup, inspect all joints with a flashlight and mirror. Re-tighten clamps after an initial heat cycle.
  8. Schedule a professional dyno tune: Do not attempt to drive the car hard on a base map. An engine is an expensive lesson. Pay a tuner who has experience with Stillen or APS kits specifically.

Additional Resources

For further reading and community support, consider these external sources:

Conclusion

Installing a Stillen or APS turbo kit on your Z is a demanding but deeply rewarding project. The most common challenges—fitment conflicts, electrical gremlins, exhaust leaks, cooling integration, and tuning complexity—can all be managed with careful planning, patience, and the right tools. By understanding these issues before you start, you can avoid many mistakes that plague first-time installers. Dedicate time to dry-fitting components, use high-quality gaskets and clamps, and never compromise on tuning. With proper execution, your Z will deliver the reliable high-horsepower experience you built it for.