S2000 valve spring and retainer limitations

The stock valve springs and retainers in the S2000 are widely acknowledged for their limitations. Notably, the original equipment manufacturer (OEM) retainers are prone to cracking, particularly in the AP1 models, leading to valve drops and catastrophic engine failures. Furthermore, the OEM springs fail to accommodate the valve lift necessary for substantial gains in naturally aspirated power.

In the aftermarket, valve spring kits often fall short in providing improved lift capacity, durability, or value. Many of these kits do not support lifts beyond 13mm. Others feature titanium retainers that, despite their design intent, have led to instances of bending or excessive wear among S2000 owners. And while there are kits that meet the requirements for lift, durability, and weight reduction, their pricing often exceeds $800, making them a less accessible option.

Driven by the need for a superior solution, we embarked on the development of a valve spring kit that supports greater lift and enhanced durability without compromising the total cost of ownership. Our goal is to deliver performance and reliability in a package that represents a prudent investment for S2000 owners.

Cost optimizing design

Central to our cost-optimization strategy is the reuse of OEM bases and keepers. The OEM bases serve the simple yet crucial function of anchoring the bottom of the spring, and we see no disadvantage in their continued use. Our design philosophy is to engineer our valve springs to be compatible with the OEM base, rather than creating a new base to fit a standard off-the-shelf spring. This approach not only conserves the integrity of the original design but also eliminates the need for replacing valve seals when reusing OEM valves, further diminishing the total costs.

Moreover, our research indicates that the AP1 OEM keepers are robust, with no notable issues concerning reliability or durability. Their weight is also sufficiently optimized, negating any need to alter their shape or material composition for weight reduction. Consequently, our retainers are engineered to accommodate OEM keepers. By leveraging the existing OEM components — base spring locators and keepers — we substantially lower both the immediate and long-term total cost of ownership (TCO). We specifically utilize the AP1 keepers due to their ubiquity and larger circumference compared to the AP2 counterparts, ensuring broader compatibility and ease of use.

*Note the AP1 keepers do not have any issues unlike the potential cracking of the AP1 retainers.

Single Spring

A pivotal aspect of our design philosophy is the adoption of a single valve spring configuration. Single springs are advantageous due to their reduced mass compared to dual spring setups, leading to lower momentum and stress within the valvetrain. This reduction in mass directly translates to enhanced valve control and the capacity to sustain higher RPMs at comparable spring rates.

There is a prevalent misconception in the industry that dual valve springs offer greater reliability than single springs by providing a fail-safe mechanism should one spring fail. However, this belief is unfounded. In a dual spring system, each spring is engineered to contribute only a portion of the required pressure to maintain valve integrity at elevated RPMs. Consequently, if one spring were to fail, the remaining spring would not be able to sustain the necessary pressure alone. This would likely result in a rapid second failure or valve float, ultimately leading to catastrophic engine damage through piston-to-valve or valve-to-valve contact.

Higher spring strength

URGE designs Ultra Valve Spring kit uses the highest quality Chrome Silicon Vanadium (CrSiV) alloy with a thicker wire diameter, providing valve spring liner rate of 341 lbs per inch.  A stronger spring rate improve valve control at higher RPMs and reduces the number of coils needed increasing valve lift support to 0.650” or 16.5mm.  Fewer coils also means less weight which further supports higher RPM.

Below convey the number of coils for the URGE designs Ultra Valve Spring (right, 5 coils) vs OEM (left, 6+ coils)

URGE designs Ultra Springs, higher strength springs weigh 10% less than OEM

Spring Endurance Enhancements

In addition to enhancing valve lift and redline capabilities, URGE Design’s Ultra-Valve Springs are engineered to improve spring endurance significantly. It is well-understood that most aftermarket springs are susceptible to degradation from intensive use, particularly at high RPMs or during track sessions, and thus should be routinely replaced as part of maintenance. However, URGE Design’s Ultra Valve Springs undergo a rigorous process of shot peening and heat treatment to mitigate surface and sub-surface stresses that are inherent in the manufacturing process. Such stresses can exacerbate under demanding conditions, diminishing spring tension and potentially causing failure. The shot peened and heat-treated material utilized in URGE Design’s Ultra-Valve Springs has been demonstrated in various high-stress applications to retain full spring pressure, even under repeated and intense usage.

valve spring Retainer Materials

Another misconception prevalent in the market is the belief that titanium retainers are not robust enough to withstand high lifts and RPMs. This is partly because some aftermarket spring kits have shown signs of excessive wear or bending. One manufacturer even categorizes their titanium retainers as consumables that require frequent replacement.

Countering this narrative, URGE Design’s Ultra Valve Spring kit incorporates Ti-17 titanium alloy, one of the most formidable titanium alloys available, boasting a yield strength greater than 1100 MPa. This makes it approximately 30% stronger than the more commonly used Ti 6Al-4V alloy. Furthermore, Ti-17 exhibits superior surface hardness, with a rating of HRC 39-40 compared to Ti 6Al-4V’s HRC 36, which translates to reduced wear rates. When compared to steel, Ti-17 also demonstrates roughly 10% greater strength than quenched 4140 chromoly steel, often used in steel spring retainers.

For those who may still harbor doubts regarding the capabilities of Ti-17, it may be compelling to note that this alloy is employed in the manufacture of turbofan blades, which operate under some of the most strenuous conditions imaginable where failure is not an option.

Titanium retainers weigh about 40% less than steel retainers supporting a few hundred RPM higher redline and reduce overall stress in the valve train, increasing longevity.

The URGE designs Ultra Valve Spring retainers (left) weigh about 40% less than the OEM retainers(right)

Overall, the URGE designs Ultra Valve spring kit weigh >15% less than OEM and 20% less when considering the top end weight all while improving valve lift support, higher RPM control and increased durability