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Manley 11573-8 Manley Severe Duty Series Stainless Steel Valves

Manley 11573-8 Manley Severe Duty Series Stainless Steel Valves

$278.00
$278.00
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The Manley 11573-8 Manley Severe Duty Series Stainless Steel Valves are high-performance engine valves engineered for intake and exhaust duty in street, strip, and marine engines. As the gateway controlling airflow into and out of the combustion chamber, valve quality directly affects flow, sealing, and high-RPM stability. These valves are designed for enthusiasts who demand consistent performance at elevated RPM.

CNC-machined from premium stainless steel, these valves feature a precision-ground head diameter with an undercut stem for improved flow at low lift. The 45-degree seat angle is standard for most applications, with a 30-degree back cut for flow optimization. The stem diameter is selected for the right balance of strength and reduced weight, and the tip is selectively hardened for compatibility with mechanical and hydraulic roller lifters. Hardened tip depth is 0.120-inch for compatibility with aggressive rocker arm geometry. Concave underhead geometry improves flow at low and mid lift values by up to 5% over conventional tulip-style designs.

These valves are compatible with 7-degree or 10-degree locks and standard spring retainers. The reduced stem weight compared to standard OEM valves lowers the overall reciprocating mass of the valvetrain, reducing the spring pressure required for valve float control. Rocker arm clearance is generous thanks to the optimized stem-to-head transition. Stellite-faced exhaust versions resist oxidation and wear at high exhaust gas temperatures, extending valve life in sustained high-RPM operation. Each valve is individually inspected for concentricity, stem straightness, and surface finish before shipment.

Switching to these premium valves reduces valvetrain weight, improves flow, and extends service life. Whether you are freshening up a set of iron heads or building aluminum castings for a 700+ HP combination, these valves meet the demands of aggressive cam profiles and high spring pressures. Order your Manley 11573-8 Manley Severe Duty Series Stainless Steel Valves and finish your cylinder head build right.
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Frequently Asked Questions

What head diameter and stem size does this Manley Severe Duty Series come in?

These valves are available in head diameters of 1.94, 2.02, 2.05, and 2.08 inches for intake and 1.50, 1.55, 1.60 inches for exhaust to match various cylinder head configurations. Stem diameter measures 11/32 inch standard or 5/16 inch for high-flow applications requiring reduced flow obstruction. Length options include 5.000, 5.025, and 5.100 inches for small block and 5.300 inches for big block applications. These valves feature undercut stems reducing diameter by 0.020 inch just below the head to improve airflow by 5 to 8 percent at 0.300 inch lift.

How do these Manley Severe Duty Series resist heat and wear in high-RPM racing conditions?

These valves are constructed from 21-4N stainless steel with a hardened tip and nitride-coated stem for wear resistance at sustained RPM above 7,500. Inconel exhaust valve options handle exhaust gas temperatures up to 1,600 degrees Fahrenheit without tuliping or stretching common in stock valves above 650 horsepower. The one-piece friction-welded design of these valves eliminates head separation failure at spring pressures exceeding 400 pounds open. For endurance racing, these valves maintain stem-to-guide clearance within 0.0015 to 0.0025 inch through 500 miles of competition at 8,000 RPM.

Can these Manley Severe Duty Series be installed in factory cast iron cylinder heads without modifications?

Yes, these valves drop into factory cast iron cylinder heads with stock 1.94/1.50 or 2.02/1.60 valve sizes but require a three-angle valve job for proper seat concentricity within 0.002 inch runout. Bronze valve guides should be used with these valves to maintain stem-to-guide clearance at 0.0015 to 0.0020 inch for street performance. For springs, these valves require installed heights of 1.700 to 1.800 inches with retainers and keepers designed for 7-degree lock angles. Spring pressure should measure 110 to 140 pounds on the seat and 280 to 350 pounds open depending on your camshaft lift profile.

What spring pressure and retainer combination works best with these Manley Severe Duty Series?

These valves pair best with dual valve springs delivering 120 to 150 pounds seat pressure at 1.800 inch installed height and 330 to 380 pounds open pressure at maximum lift. Titanium retainers weighing 8 to 10 grams reduce reciprocating mass by 35 to 40 percent compared to steel retainers, allowing RPM capability up to 7,800. For these valves using 10-degree locks, ensure retainer-to-valve stem clearance of 0.050 inch minimum to prevent retainer contact with the valve seal. COMP Cams 740-series or equivalent springs with damper provide the correct spring rate of 350 to 400 pounds per inch.

Do these Manley Severe Duty Series require hardened exhaust seats for unleaded fuel operation?

These valves with stainless steel construction do not require hardened exhaust seats for unleaded fuel operation as the 21-4N material resists seat recession at normal operating temperatures. The valve face angle is 45 degrees with an optional 30-degree back cut to improve low-lift flow by 7 to 10 percent. For engines running primarily on E85 or race gas, these valves maintain seat integrity through 500 hours of operation at 200 to 220 degrees Fahrenheit head temperature. Hardened seats are recommended only for engines exceeding 500 horsepower or with sustained operation above 6,500 RPM.

What is the weight difference between these Manley Severe Duty Series and factory OEM valves?

These valves weigh approximately 95 to 110 grams for a 2.02 intake valve compared to 120 to 135 grams for factory OEM equivalents, a reduction of 20 to 25 percent in reciprocating mass. The lightweight design reduces valve float tendency and allows 300 to 500 RPM higher shift points with the same spring package. Stem diameter of 11/32 inch saves 8 to 10 grams per valve versus 3/8 inch stem valves while providing adequate strength for spring pressures up to 380 pounds open. Total rotating assembly weight reduction of 150 to 200 grams improves throttle response and valvetrain stability.