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Proven Fatigue Tests: The Severe Duty? Valves have undergone rigorous fatigue tests. In normal operation, valves experience 20,000 to 25,000 lbs of applied stress. When valves bounce on the seat, this stress soars to 40,000 to 60,000 lbs. Manley exhaust valves, tested at 40,000 psi and 1400?F, impressively endured up to 100,000,000 (one hundred million) cycles. In contrast, competitors' offerings failed after just 100,000 cycles, showcasing a staggering 1000 times better fatigue life.Designed for High Temperature Gasoline Engines: Engineered for superior performance in high-temperature gasoline engines.Chrome Stems and Hard Tips: Incorporating chrome stems and hard tips for enhanced durability and longevity.Optimized Combustion: Swirl polished under head areas and fully machined combustion faces for improved airflow and combustion efficiency.XH-428 for Exhaust: No competitor worldwide offers the exceptional XH-428 as exhaust valve material. It boasts nearly double the ultimate tensile strength at 1500?F compared to the competition's EV-8.NK-844 for Intake: Our intake valve material, NK-844, is equally unmatched, displaying over four times the ultimate tensile strength of the competition's best intake valve material at 1000?F.