This aftermarket intake manifold is designed for the SYM Symphony 125I ST 125cc fuel-injected engine, fitting 2017-2020 model years and cross-referenced to OEM number 1711A-Z5C-010. The intake manifold serves as the critical air distribution component, channeling filtered air from the throttle body to the cylinder head intake port while maintaining laminar flow and minimal pressure drop.
In the 125cc 4-stroke single-cylinder architecture, the intake manifold’s geometry significantly influences the engine’s torque curve and throttle response. The runner length of 145mm is tuned to exploit pressure wave dynamics, creating a ram effect that enhances cylinder filling at low-to-mid RPM ranges where urban scooters spend most of their operating time. The 22mm internal diameter is calculated to maintain air velocity above 50 m/s at peak power RPM, ensuring good fuel atomization and minimal fuel dropout on the manifold walls. The plenum volume of 180cc provides adequate damping of pressure pulsations from the intake valve opening events.
Constructed from glass-reinforced polyamide 6,6 (PA66-GF30), the manifold withstands intake air temperatures up to 120°C without deformation or creep. The 30% glass fiber content provides the structural rigidity necessary to maintain seal integrity against the cylinder head flange, while the polymer’s low thermal conductivity prevents heat soak from the engine that could reduce volumetric efficiency. The gasket surface is machined flat within 0.05mm to prevent vacuum leaks that would cause lean running and erratic idle. The fuel injector bore is machined to H7 tolerance with a 7° lead-in chamfer to ensure proper O-ring compression and injector alignment.
Technical parameters: material PA66-GF30; runner length 145mm; internal diameter 22mm; plenum volume 180cc; injector bore Ø14mm H7; mounting flange bolt pattern M6x1.0; temperature rating -40°C to 120°C continuous.
The manifold includes the integral fuel injector mount, vacuum tap for the fuel pressure regulator (if applicable), and the breather hose connection. The throttle body mounting flange accepts the standard 28mm bore throttle body used on the Symphony 125i platform. All hose barbs are molded with retention ridges to prevent hose disconnection under vibration.
Replacement is necessary when: vacuum leaks cause lean running codes (P0171), the injector bore shows damage from improper removal, the mounting flange is cracked from over-torquing, or the internal surface shows carbon buildup exceeding 1mm thickness. During installation, use a new manifold gasket and torque the mounting bolts to 10 Nm in a cross pattern to prevent flange distortion. Verify that all vacuum hoses and the breather connection are properly seated before starting the engine.
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