Introduction
Valve springs are one of the most critical components in any engine, directly affecting airflow, RPM capability, and long-term reliability. On Nissan’s classic A-series engines — the A14 and A15 — the factory (OEM) valve springs were designed for low to moderate RPM daily driving. They were never intended for high-performance use.
As soon as an A-series engine is upgraded with a performance camshaft, raised rev limit, or forced induction, the limitations of the OEM valve springs become clear. This is where the STK Dual Racing Valve Spring Kit proves its value, offering superior valve control, durability, and performance under demanding conditions.
What OEM Valve Springs Are Designed For
OEM valve springs in the A14 and A15 engines were engineered to:
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Operate reliably with factory camshaft profiles
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Maintain stability within standard factory RPM limits
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Prioritise longevity, smoothness, and emissions compliance
For standard street use, OEM springs are sufficient. However, once performance demands increase, several weaknesses become evident:
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Valve float at higher RPM due to insufficient spring pressure
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Valve bounce caused by weak closing force
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Poor compatibility with aggressive camshaft lift and duration
When pushed beyond stock limits, OEM valve springs quickly become the weakest link in the valvetrain, limiting performance and increasing the risk of engine damage.
Why the STK Dual Racing Valve Spring Kit Is Better
The STK Dual Valve Spring Kit for Nissan A14 and A15 engines is purpose-built to address every limitation of OEM springs. It is designed for performance, durability, and precise valve control.
1. Dual Spring Design for Superior Control
Unlike the OEM single-spring setup, the STK kit uses a dual spring configuration consisting of an inner and outer spring working together. This design provides:
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Increased seat and open pressure for improved valve control
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Reduced valve float at high RPM
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Improved resistance to harmonic vibration and resonance
The result is accurate valve movement that follows the camshaft profile precisely, even under aggressive acceleration and high engine speeds.
2. Motorsport-Grade Materials and Manufacturing
STK valve springs are manufactured using high-grade chrome-silicon, a material chosen for its strength, heat resistance, and fatigue durability. Each spring undergoes advanced manufacturing processes, including:
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Precision heat treatment to enhance strength and lifespan
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Shot peening to reduce surface stress and prevent cracking
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Tight tolerance finishing for consistent installed height and pressure
These processes ensure that STK valve springs maintain performance under sustained heat and high RPM conditions where OEM springs fail.
3. Designed for High RPM and Performance Camshafts
Performance camshafts place significantly higher demands on valve springs. Increased lift, faster ramp rates, and longer duration all require stronger and more stable spring pressure.
STK dual valve springs are designed to:
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Support aggressive camshaft profiles
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Maintain consistent pressure throughout the full valve travel
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Prevent coil bind and pressure loss at high RPM
This makes them ideal for naturally aspirated performance builds, track cars, and forced induction A14 and A15 engines.
4. Improved Durability and Reliability
High-performance engines place extreme stress on valvetrain components. The dual spring design of the STK kit spreads the workload across two springs, reducing fatigue and extending service life.
Key durability benefits include:
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Reduced spring stress per coil
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Improved resistance to heat-related sag
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Consistent performance over repeated high-RPM cycles
This translates to fewer failures, better reliability, and longer engine life in demanding applications.
Real-World Performance Benefits
Upgrading from OEM to STK dual valve springs delivers clear advantages:
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More stable power delivery at high RPM
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Higher safe rev limits with reduced risk of valve float
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Improved engine reliability under performance conditions
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Full compatibility with aftermarket camshafts
Drivers will notice smoother power at the top end and increased confidence when pushing the engine hard.
Conclusion: Why STK Is the Smarter Upgrade
For any Nissan A14 or A15 engine that goes beyond basic daily driving, the STK Dual Racing Valve Spring Kit is a clear upgrade over OEM components.
It offers:
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Stronger and more consistent valve control
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Compatibility with performance camshafts and higher RPM limits
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Superior durability under heat and mechanical stress
Motorsport-level engineering tailored to A-series engines
Where OEM valve springs limit performance and reliability, STK dual valve springs unlock the full potential of the engine, making them the preferred choice for enthusiasts, racers, and serious engine builders.