Building a 400‑horsepower VQ37 engine is a rewarding goal for any Nissan or Infiniti enthusiast. The VQ37, whether in the VQ37VHR or VQ37HR variant, is a robust 3.7‑liter V6 that responds well to modifications. However, reaching this power level without sacrificing daily drivability or long‑term durability requires a careful balance of OEM Nissan parts and carefully selected aftermarket supports. This guide breaks down the essential components, explains how they work together, and provides the knowledge you need to build an engine that will deliver reliable power on both the street and the track.

Understanding the VQ37 Engine Platform

The VQ37 engine family includes the VQ37HR (High Response) and the VQ37VHR (Variable High Response), which adds Nissan’s VVEL (Variable Valve Event and Lift) system. Both versions share a stout cast‑iron block, forged steel crankshaft, and a 10.6:1 compression ratio. The VVEL system on the VQ37VHR provides exceptional throttle response and mid‑range torque, but it also introduces additional complexity for tuning. For a 400 HP build, the VQ37VHR is the more common starting point because its factory heads and valvetrain can handle the extra airflow with minimal internal work. Understanding these nuances helps you make informed decisions about which components to upgrade and which to leave alone.

Key factory specifications of the VQ37VHR include a 95.5 mm bore, 86.0 mm stroke, and a redline around 7,500 RPM. Stock horsepower is roughly 330 at the crank (about 280 at the wheels for a 370Z or Infiniti Q60), meaning you will need to gain about 70‑80 wheel horsepower to hit a safe 400 at the crank, or roughly 330‑350 at the wheels. This is a very achievable target with the right combination of bolt‑ons and tuning, provided you respect the engine’s limitations.

OEM Nissan Parts: The Foundation of a Durable Build

Using genuine OEM Nissan parts where strength and tolerances matter most is the single best way to ensure your 400 HP VQ37 stays together for thousands of miles. OEM components are designed to exact specifications for fit, material, and heat treatment. Aftermarket alternatives can be excellent, but many builders rely on factory parts for the block, rotating assembly, and sealing surfaces.

Engine Block and Bottom End

The OEM VQ37 engine block is already extremely strong. Factory blocks have supported over 600 HP with proper tuning. For a 400 HP target, the only recommended upgrade is to install ARP main studs and ARP head studs to maintain consistent clamping force under boost or high RPM. Otherwise, the OEM block, main caps, and bearing clearances are more than adequate.

OEM pistons are cast but strong enough for naturally aspirated builds up to about 400 HP. If you plan to add forced induction later, consider aftermarket forged pistons (e.g., CP‑Carillo or JE) to handle detonation. For a pure naturally aspirated 400 HP, OEM pistons with fresh rings and a proper hone will work reliably.

The factory forged steel crankshaft is a standout component. It is cross‑drilled, nitrided, and balanced from the factory. You can safely turn it to 7,500 RPM without modifications. Similarly, the OEM connecting rods are powdered metal but strong enough for 400 HP. Many builders reuse them with new rod bolts (ARP 2000) for added safety. Replacing the factory rod bearings with King XP or ACL Race bearings is recommended for increased clearance and oil film thickness under high loads.

Valvetrain and Cylinder Heads

On the VQ37VHR, the OEM cylinder heads flow very well from the factory. The VVEL system provides variable valve lift and timing, which gives excellent low‑speed torque and high‑RPM power. For 400 HP, the stock heads need only a light port match and a valve job. Do not use oversized valves unless you are building a full race engine. The OEM camshafts are fine; the VVEL actuator essentially changes cam profile on the fly. Aftermarket camshafts for VQ37VHR exist (e.g., from JWT or Kelford), but they require a custom tune and can make idle quality poor. Stick with the OEM cams and VVEL for a reliable, street‑friendly 400 HP.

Replace the valve springs with upgraded units (e.g., Z1 Motorsports offers a set of dual springs) to prevent valve float at the higher RPM you will use. The factory retainers and keepers can be reused.

Gaskets and Seals

Never scrimp on gaskets. Use only OEM Nissan head gaskets, valve cover gaskets, and oil pan gaskets. Aftermarket head gaskets from Cometic or Tomei are acceptable if you need a different thickness (for compression ratio adjustments), but the OEM multi‑layer steel gaskets are excellent up to high boost levels. Replace all coolant hoses with OEM or high‑quality silicone hoses to prevent leaks under higher heat.

Aftermarket Supports: Unlocking the Extra Horsepower

Once the internal foundation is solid, aftermarket parts are what get you to 400 HP. The key is to choose components that work together without creating bottlenecks or causing drivability issues.

Intake and Exhaust Airflow

The stock intake system on the 370Z and Infiniti Q60 is restrictive above 350 HP. A cold air intake (CAI) such as the Stillen Gen 3 CAI or the Z1 Motorsports 3‑inch intake adds significant airflow. Pair this with a larger throttle body (76 mm or 80 mm) from NWP Engineering or Z1 Motorsports to reduce pressure drop. The aftermarket throttle body should be matched to the intake manifold. On the exhaust side, a set of long‑tube headers (e.g., ARK Performance or Berk Technology) and a full 3‑inch exhaust with high‑flow catalytic converters or test pipes will unlock at least 15‑20 wheel horsepower. A resonated test pipe is recommended to keep noise reasonable.

Fuel System Upgrades

Stock fuel injectors (at about 320 cc/min) will max out around 360‑380 crank horsepower. For 400 HP, you need upgraded injectors in the 550‑650 cc/min range. DeatschWerks 650cc drop‑in injectors are a popular choice. You will also need a higher‑flow fuel pump. The factory pump in the 370Z can provide enough fuel for about 400 HP with a boost‑a‑pump or by rewiring, but a safer approach is a Walbro 255 LPH or AEM 320 LPH in‑tank pump. For flex‑fuel capability (E85), upgrade to a 450 LPH pump and injectors around 850 cc/min.

Engine Cooling

Power adds heat. The stock radiator is marginal for sustained high‑power driving. Upgrade to a Mishimoto or Koyo aluminum radiator with an high‑flow thermostat (70°C opening). An oil cooler is mandatory for any track use. The CZP (Concept Z Performance) oil cooler kit with a Setrab core is a proven choice. Also consider a power steering cooler if you will be autocrossing or road racing.

Engine Management and Tuning

No 400 HP build succeeds without a proper tune. The stock ECU can be reprogrammed via Uprev Osiris, Ecutek, or Haltech Elite plug‑in ECUs. For a naturally aspirated build, a mail‑order tune from a reputable shop like AdminTuning or RS Enthalpy will work well. If you have added VVEL aftermarket adjustments or need fine control, a standalone ECU (Haltech, MoTeC, or AEM Infinity) may be necessary. Expect to pay $500‑1,500 for a professional dyno tune. The tuner will adjust fuel maps, ignition timing, VVEL lift and timing curves, and knock sensor sensitivity. A good tune is the difference between a reliable 400 HP and a blown engine.

Drivetrain Upgrades

400 HP will stress the stock clutch and differential. Replace the clutch with a South Bend Stage 3 or ACT Heavy Duty unit. The stock 370Z CD00A manual transmission can handle the power, but the differential uses an open differential or viscous limited‑slip. Upgrade to a OS Giken or KAAZ clutch‑type LSD for better traction on corner exit. Also consider upgrading the half shafts to stronger units from DSS (Drive Shaft Shop) or Z1 Motorsports if you run sticky tires.

Balancing Power and Reliability: Key Considerations

Reaching 400 HP is not just about adding parts; it is about ensuring every system in the car works in harmony. Below are critical areas often overlooked.

Oil System

The VQ37 is prone to oil starvation under high lateral G‑forces. An Accusump or a Killer B Motorsport oil pan with internal baffles is highly recommended. Use a high‑quality synthetic oil, such as Motul 300V 5W‑40 or Red Line 5W‑30. Change oil every 3,000 miles or after every track day.

Air‑Fuel Ratio and Knock Control

Do not exceed an air‑fuel ratio of 12.5:1 under full throttle (for pump gas). Use a wideband O2 sensor (AEM or Innovate) mounted in the downpipe for data logging. Knock should be kept at zero; any audible knock requires immediate ignition retard or richer mixture. A quality tune with adequate safety margins is essential.

Weight Reduction

Every pound matters for both performance and cooling. Remove unnecessary interior bits, swap to lightweight seats, and use a lightweight battery (e.g., Antigravity AGM). The less weight the engine has to move, the less heat it generates and the longer it lasts.

Common Mistakes When Building a 400 HP VQ37

  • Over‑scaling upgrades: Using a huge throttle body with stock intake manifold or small camshaft creates an imbalance that hurts power and drivability.
  • Ignoring the PCV system: High cylinder pressure can push oil into the intake. Install an oil catch can (Radium Engineering or Mishimoto) to keep the intake clean.
  • Cheap tuning: A mail‑order tune is fine for basic bolt‑ons, but for camshafts or VVEL changes you need a professional dyno tune. Do not rely on “off‑the‑shelf” maps.
  • Neglecting cooling: Many builds add power but forget to upgrade the radiator, oil cooler, and thermostat. Engine heat soak leads to detonation and pre‑ignition.
  • Using wrong fuel: 400 HP on pump 91 octane is possible with conservative timing, but 93 octane (or E85) gives you a safety margin. Never run lower than 91.

Cost Breakdown for a Reliable 400 HP VQ37 Build

This section provides rough estimates (USD) for parts and labor, assuming you do most of the work yourself. Prices vary based on brand and supplier.

  • Intake and tune: $1,200‑1,800 (including ECU reflash and dyno time)
  • Headers and exhaust: $1,000‑1,500 (cat‑back + headers)
  • Fuel injectors and pump: $500‑800
  • Cooling system (radiator, oil cooler, thermostat): $600‑1,000
  • Clutch and flywheel: $800‑1,200
  • Gaskets, studs, bearings, seals: $400‑600
  • LSD and half shafts: $1,500‑2,500 (if needed)
  • Miscellaneous (catch can, hoses, fluids): $200‑400

Total for a solid build: $6,000‑9,000 plus the cost of the donor car. This may seem high, but it ensures reliability and avoids expensive failures.

Maintenance for a 400 HP VQ37

Once built, the engine will need more frequent maintenance than stock. Follow this schedule:

  • Oil change: Every 3,000 miles or after 10 hours of track time.
  • Spark plugs: NGK LFR7AIX (one step colder) every 15,000 miles.
  • Serpentine belt: Inspect every 10,000 miles; replace annually.
  • Coolant flush: Every two years with Nissan genuine coolant.
  • Valve lash inspection: Check every 30,000 miles (shim‑over‑bucket design on VQ37VHR).

Regularly inspect all hoses, vacuum lines, and electrical connections. A 400 HP engine is more sensitive to small issues than a stock engine. Catching a leaking injector or a loose boost hose early can save you from a rebuild.

Conclusion

A 400 horsepower VQ37 is a thrilling, reliable powertrain when built with care. OEM Nissan parts provide the strong foundation needed for longevity, while strategic aftermarket supports deliver the additional airflow, fuel, and cooling required to hit that power target. The key is not to over‑complicate the build—stick with proven components, invest in professional tuning, and don’t neglect the supporting systems. Whether you are aiming for a fast daily driver or a weekend track car, this recipe will give you the dependable power you are looking for. Start with a healthy engine, use quality parts, and you will enjoy many miles of tire‑shredding performance.