Understanding Supercharger Basics

Before diving into the specific sizes, it is essential to understand how a supercharger operates. Unlike a turbocharger that uses exhaust gases to spin a turbine, a supercharger is mechanically driven off the engine – usually via a belt connected to the crankshaft. A Roots-type supercharger uses a pair of meshing lobes to trap and move air from the intake inlet to the outlet. This positive displacement design means that for every revolution of the rotors, a fixed volume of air is forced into the engine. The result is immediate, linear power that builds with engine RPM, offering a driving experience that feels more like a naturally aspirated engine with a massive displacement increase. The size of the rotors (typically measured in millimeters) directly correlates with the volume of air moved per revolution – hence the significance of 68mm versus 78mm rotors for your 370Z.

The 68mm Roots Supercharger for the 370Z

The 68mm Roots supercharger kit is often seen as the "entry-level" forced induction option for the Nissan 370Z, but that label undersells its capability. This rotor size is commonly paired with a 1.9L to 2.3L supercharger unit (such as the Eaton TVS or similar). It provides a moderate increase in air volume without drastically altering the engine's natural characteristics.

Performance Characteristics and Dyno Numbers

On a typical 370Z with bolt-on modifications (intake, exhaust), a 68mm Roots supercharger will produce approximately 420–480 wheel horsepower (whp) and 380–420 lb-ft of torque, depending on boost pressure (typically 6–9 psi) and fuel quality. The power delivery is exceptionally linear, with a strong mid-range punch. The 68mm excels at low-end and mid-range torque, making the car feel significantly quicker from a stoplight or during daily highway merging. Throttle response is instantaneous because the supercharger is always engaged.

  • Low-end torque: Peak torque often arrives by 3000–3500 RPM, providing a "push you back in the seat" sensation.
  • Throttle response: No lag – the power is directly proportional to pedal position.
  • Drivability: Retains factory-like drivability for daily commuting, traffic, and normal driving conditions.
  • Heat management: Lower boost levels mean less heat generation, reducing the demand for an intercooler (many kits use an air-to-water or air-to-air intercooler, but heat is manageable).

When to Choose the 68mm

The 68mm is ideal for the enthusiast who wants a reliable, street-friendly power increase without the complexity or cost of a fully built engine. It works well with the factory fuel system (with an upgraded fuel pump) and does not necessarily require forged internals, especially below 500 whp. This setup is also popular for Z1 Motorsports and other tuners as a solid foundation for a street-driven 370Z.

The 78mm Roots Supercharger – Maximum Output

Stepping up to the 78mm rotor size (common in larger supercharger units like the 2.8L or 3.0L Eaton TVS series) dramatically increases the air-moving capacity. This is a serious performance upgrade aimed at owners who are chasing high horsepower numbers and are willing to invest in the requisite supporting modifications.

Performance Characteristics and Dyno Numbers

With a 78mm Roots supercharger, boost levels typically range from 10–14 psi, even higher with smaller pulleys. Power output can easily exceed 550 whp on a well-tuned car with proper fuel (E85 or race gas), and some setups push beyond 650 whp with built engines. The torque curve is broader and taller; the engine pulls hard from 2500 RPM all the way to the redline. However, this level of power requires more attention to engine internals, fuel delivery, and cooling.

  • Higher boost levels: More air per revolution translates directly to higher potential power.
  • Top-end power: The larger rotors maintain airflow efficiency at high RPM, preventing the drop-off that smaller superchargers experience.
  • Racing and track use: The 78mm is suited for drag racing, time attack, and spirited track days where maximum power is prioritized.
  • Cooling demand: Higher boost generates significant heat; an efficient intercooler (or charge cooler) and possibly water-methanol injection are necessary.

When to Choose the 78mm

The 78mm supercharger is for the owner with a clear goal of building a high-horsepower 370Z, often with a built engine, upgraded transmission (the OEM CD009 can handle up to ~600 whp with care), and a robust cooling system. It is not recommended for a purely daily driver unless you are prepared for the higher maintenance and fuel costs. For those seeking elite performance, companies like Stillen offer supercharger kits that utilize larger rotor sizes for maximum output.

Comparative Analysis: 68mm vs 78mm Roots Supercharger

To make an informed decision, you must evaluate the differences across several key dimensions:

Aspect 68mm (2.3L) 78mm (2.8L-3.0L)
Typical Boost (psi) 6–9 psi 10–14 psi
Estimated WHP (pump gas) 420–480 whp 500–600+ whp
Low-End Torque Excellent, early peak Very strong, wider torque plateau
Heat Generation Moderate High – requires upgraded cooling
Engine Internals Stock forged rods/pistons OK (if kept below ~500 whp) Built engine highly recommended
Fuel System Upgraded fuel pump + maybe injectors Full fuel system: pump, injectors, lines, FPR, return system
Drivability Near stock Still good but more aggressive
Cost (kit + labor) ~$5,000–$7,000 ~$7,500–$10,000+

Power vs. Reliability Trade-off

One of the most important considerations is the strain on the VQ37VHR engine. The 370Z's factory internals are relatively strong (forged rods, cast pistons), but they have limits. A 68mm kit at conservative boost levels is well within the safe zone. The 78mm kit pushes the boundaries – you will likely need forged pistons and rods, upgraded valve springs, and possibly oil pump upgrades to handle the extra cylinder pressure and RPM. Failure to do so can lead to ring land fractures or rod failure. Always budget for these supporting modifications when considering the larger supercharger.

Supporting Modifications: What You Need for Each Setup

No supercharger upgrade works in isolation. The increased airflow demands more fuel, better spark, and improved heat dissipation. Below is a breakdown of the necessary supporting parts for both sizes.

Fuel System Upgrades

For 68mm: A higher-flow fuel pump (such as Walbro 255 or 450) and 650–750cc injectors are typically sufficient. The stock fuel pressure regulator can often be retained if the pump is adequate. Some tuners recommend a return-style fuel system for easier tuning and consistency.

For 78mm: You will need a full return-style fuel system. This includes a larger fuel pump (e.g., Walbro 450 or dual pumps), 1000cc or larger injectors, an adjustable fuel pressure regulator, and upgraded fuel lines. E85 compatibility is almost mandatory to take full advantage of the higher boost levels and to help cool the intake charge.

Cooling System

Heat is the enemy of forced induction performance. The 370Z's engine bay is tight, and proper intercooling is crucial.

  • Intercooler: Air-to-air is common, but air-to-water (charge cooler) offers shorter piping and lower lag, ideal for Roots blowers. For 78mm, an upgraded core or a dual-pass cooler is recommended.
  • Additional cooling: Upgraded radiator (aluminum, increased capacity), oil cooler, and transmission cooler (especially for automatic) are recommended for sustained spirited driving. The 78mm setup may also benefit from a water-methanol injection kit to lower intake temps and reduce knock.
  • Thermal management: Consider hood vents or a vented hood to reduce underhood temperatures and improve heat extraction.

Engine Management and Tuning

Both setups require a proper ECU tune. The 370Z's ECU can be reflashed via platforms like UpRev or ECUTEK. For the 68mm, a flash tune with updated fuel and ignition maps is enough. For the 78mm, a stand-alone ECU (such as Haltech or MoTeC) may be necessary to achieve safe and precise control, especially if using E85 or high boost. Professional dyno tuning is non-negotiable – a poor tune can destroy an engine quickly. Many reputable shops like Torq Performance specialize in 370Z forced induction tuning.

Installation Considerations and Labor

Installing a Roots supercharger is a major mechanical job. While many enthusiasts can do it in a well-equipped garage, it typically takes 15–25 hours for a first-timer. Key steps include:

  • Removing the front bumper, grille, and radiator support to access the front of the engine for pulley and belt routing.
  • Replacing the intake manifold with the supercharger assembly and its associated ducts.
  • Routing boost pipes, intercooler, and coolant lines (for charge coolers).
  • Updating the accessory belt – often a dedicated shorter belt and idler pulleys.
  • Installing fuel injectors and tuning the ECU.

For the 78mm, the job is more involved because additional modifications (engine build, fuel system rework) are usually performed simultaneously. Expect significantly more labor hours and cost.

Professional Installation vs. DIY

If you lack experience with forced induction installations, paying a professional shop is strongly advised. Improper belt tension, leaking hoses, or a misaligned supercharger can cause serious damage. Several well-known 370Z specialists can handle the entire process, including tuning, and often offer warranty on their work.

Choosing Based on Your Driving Use Case

To simplify the decision, match the supercharger size to your primary use:

  • Daily driver / street cruiser: 68mm. You get substantial power gains without sacrificing reliability or comfort. The car remains easy to drive in traffic, and fuel economy is still acceptable.
  • Weekend canyon carver / occasional track days: 68mm or a moderately boosted 78mm (mild pulley). The 68mm will provide plenty of excitement on tight roads. If you want to compete for lap times, the 78mm offers the headroom to grow with future upgrades.
  • Drag racing / roll racing / high-horsepower builds: 78mm. This is the only choice when you want 600+ whp. Be prepared for a built engine and full fuel system.
  • Show car / maximum power with bling factor: 78mm. The larger supercharger case often looks more impressive under the hood, and the sound of the blower whine is unmistakable.

Cost Comparison and Budgeting

Beyond the supercharger kit itself, you must account for supporting parts and labor. A realistic budget for a 68mm setup (including tune and minor supporting mods) is $7,000–$9,000. For a 78mm setup with a built engine and full fuel system, expect $12,000–$18,000 or more, depending on labor and parts quality.

Funding a supercharger installation wisely can save money – buy complete kits when possible, and avoid used superchargers unless they come with full documentation and have been inspected. Websites like Six Sigma Autosports offer comprehensive packages that include all necessary components, streamlining the process.

Final Thoughts

The 68mm vs 78mm Roots supercharger decision for your 370Z is fundamentally about your power target, budget, and willingness to support the extra stress with stronger internals and cooling. There is no "wrong" choice if it aligns with your goals. The 68mm offers an excellent, reliable step up that transforms the 370Z into a swift street machine. The 78mm propels the car into serious high-performance territory, demanding a more comprehensive build. Whichever path you choose, invest in professional tuning and high-quality parts – your 370Z will reward you with an exhilarating driving experience that few modifications can match. With proper care, a Roots-supercharged 370Z remains a dependable and exciting car for years to come.