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Porsche > 964 (911) (1989-1994) > Engine Rebuild Parts > Engine Valves / Guides / Springs >

Engine cylinder head exhaust valve. Porsche 993 C2 / C4 1996-98 ❭ 99310541906

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OE Match

99310541906/1

Product Information

Exhaust Valve - Varioram Engines
Sold each - 6 required per car

Maintain the performance, efficiency and reliability of your Porsche 993 Varioram engine with this OE Match Exhaust Valve. Designed specifically for Porsche 993 Varioram engines including M64.21, M64.22, M64.23 and M64.24 engine variants, this exhaust valve plays a critical role in the combustion process by allowing spent exhaust gases to exit the combustion chamber efficiently.

Fits:

Porsche 993 (911) C2 1996-97
Porsche 993 (911) C4 1996-97
Porsche 993 (911) RS 1996-97
Porsche 993 (911) C2S 1996-97
Porsche 993 (911) C4S 1996-97

Diagram Ref No 10

Operating under extreme temperatures and pressures, exhaust valves are among the hardest-working components within the engine. During every combustion cycle, they must withstand intense heat while maintaining an effective seal against the valve seat to preserve compression, power output and engine efficiency.

Manufactured to OE Match specifications, this exhaust valve is ideal for engine rebuilds, cylinder head refurbishment, top-end overhauls and preventative maintenance projects.

Technical Specification
Valve Head Diameter: 43.50 mm
Valve Stem Diameter: 8.00 mm
Valve Shaft Length: 109.00 mm
Valve Seat Angle: 45°
Suitable for Porsche 993 Varioram engines: M64.21 M64.22 M64.23 M64.24

What Does the Exhaust Valve Do?

The exhaust valve is responsible for controlling the exit of combustion gases from the cylinder.

Its primary functions include:

Releasing burnt exhaust gases
Maintaining combustion chamber sealing
Supporting efficient engine breathing
Preserving compression
Assisting engine performance
Supporting fuel efficiency
Maintaining smooth engine operation

Correct exhaust valve operation is essential for maintaining the power and responsiveness expected from the Porsche 993 Varioram engine.

Why Do Exhaust Valves Fail?

Exhaust valves are exposed to some of the harshest operating conditions within the engine.

Common causes of failure include:

Extreme heat exposure
Valve seat wear
Carbon build-up
High mileage wear
Detonation damage
Valve guide wear
Overheating

Over time, valves can become worn, burnt, pitted or damaged, reducing their ability to seal effectively.

Symptoms of a Worn or Damaged Exhaust Valve

Common warning signs include:

Reduced engine compression
Loss of power
Rough idle
Increased exhaust emissions
Misfires
Excessive oil consumption
Poor throttle response
Unusual engine noise

In severe cases, a burnt valve can significantly affect engine performance and drivability.

When Should Exhaust Valves Be Replaced?

Replacement is recommended when:

Carrying out a cylinder head rebuild
Performing a top-end engine overhaul
Valve seat damage is present
Compression loss is identified
Burnt valves are discovered
Valve stem wear exceeds specifications
Rebuilding a high-mileage engine
Completing a full engine restoration

Professional engine builders routinely inspect and measure all valves during rebuild work.

Why Replacement Matters

A worn exhaust valve can compromise engine performance, reliability and efficiency.

Benefits of replacement include:

Restored compression
Improved power delivery
Better engine efficiency
Smoother operation
Improved combustion quality
Reduced emissions
Increased engine reliability
Long-term engine protection

Replacing worn valves during a rebuild helps ensure the longevity of expensive engine components.

Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.

99310541906

99310541906

993.105.419.06

3342.239

864428-6

99310541943

The product you are viewing cross references to these numbers

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Valve spring. Porsche 911 1965-89 / 964 1990-94

90110590151/1

Product Information

Valve Spring
Sold each

The Porsche Valve Spring is a critical component of the valve train system fitted to numerous Porsche 911 and Porsche 964 models from 1965 to 1994. Designed to maintain precise valve operation throughout the engine's RPM range, the valve spring ensures that intake and exhaust valves close correctly after being opened by the camshaft.

Fits:

Porsche 911 1965-1968 2.0L / 912 SWB (F)
Porsche 911 1968-1973 2.2L / 2.4L / 2.7L RS LWB (F)
Porsche 911 1974-1977 2.7L / 1976-77 3.0 Carrera
Porsche 911 1978-1983 3.0L / SC
Porsche 911 1984-1986 3.2L
Porsche 911 1987-1989 3.2L G50
Porsche 911 1975-1977 3.0L Turbo (930)
Porsche 911 1978-1989 3.3L Turbo (930)
Porsche 964 (911) C2 1989-93
Porsche 964 (911) C4 1989-93
Porsche 964 (911) RS 3.6L 1991-93
Porsche 964 (911) RS 3.8L 1991-93
Porsche 964 (911) TURBO 3.3L 1991-93
Porsche 964 (911) TURBO 3.6L 1991-93

Diagram Ref No 13

In Porsche's legendary air-cooled flat-six engines, accurate valve control is essential for maintaining combustion efficiency, engine performance, reliability, and long-term durability. The valve spring works continuously under extreme mechanical stress, cycling thousands of times per minute to keep the valve train operating correctly.

Whether you're rebuilding a classic Porsche engine, restoring a 911, or carrying out a cylinder head overhaul, replacing worn valve springs helps maintain factory performance and reduces the risk of costly engine damage.

What Does the Valve Spring Do?

The valve spring is responsible for returning the intake and exhaust valves to their closed position after each opening cycle generated by the camshaft.

Its key functions include:

Maintaining correct valve timing operation
Ensuring valves close fully and consistently
Keeping the valve train under proper tension
Preventing valve float at higher engine speeds
Supporting engine compression and combustion efficiency
Protecting the valve train from instability and excessive wear

Without adequate spring tension, valves may not close correctly, leading to poor performance and potential engine damage.

Why Does the Valve Spring Fail?

Valve springs are constantly subjected to compression, heat, vibration, and high engine speeds. Over time, these factors can lead to material fatigue and a gradual loss of spring tension.

Common causes of valve spring failure include:

Metal fatigue from repeated cycling
High mileage wear
Prolonged exposure to engine heat
Over-revving the engine
Corrosion or contamination
Performance modifications increasing valve train loads
Age-related weakening of spring material
Improper engine assembly or valve train geometry

As spring pressure decreases, valve control becomes less precise, particularly at higher RPM.

Common Symptoms of Worn Valve Springs

A weakened or damaged valve spring may cause:

Loss of engine performance
Valve float at higher RPM
Rough idle
Engine misfires
Increased valve train noise
Reduced power output Inconsistent compression readings
Premature wear of valves, guides, and camshaft components

In severe cases, a broken valve spring can result in valve-to-piston contact and major engine damage.

When Should You Replace Valve Springs?

Valve springs should be inspected whenever the cylinder heads are removed and replaced if any signs of fatigue or wear are detected.

Replacement is strongly recommended:

During complete engine rebuilds
During cylinder head refurbishment
On high-mileage engines
When installing performance camshafts
If valve float is present
When spring tension falls below specification
During preventative maintenance on restoration projects
Whenever a spring shows signs of corrosion or damage

Many experienced Porsche engine builders replace all valve springs during rebuilds to ensure consistent valve train performance and long-term reliability.

Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.

90110590151

90110590150

90110590151

The product you are viewing cross references to these numbers

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Engine cylinder head exhaust valve. Porsche 993 C2 / C4 1996-98 ❭ 99310541906