The S14 and S15 generations are known for their variable valve timing, ball bearing turbos, and top mounted throttle body. A throttle body in this position places the inverted intake plenum on top, above the fuel injectors, making the top-feed conversion more difficult. Initial assessments revealed that the OEM steel idle air bypass line tubing was causing fuel rail clearance issues. To solve this, a billet IACV spacer with a threaded port was designed.
This allows the use of a rubber hose to bypass air for the idle motor while eliminating interference with the fuel rail. It was also discovered that Nissan has discontinued the S14/S14 IACV gaskets which lead to a Radium produced version which is included in the fuel rail kit and available separately. Even with the limited overhead space created by the S14/S15 intake plenum, a high quality, 0.69" (17.5mm) high flow top-feed fuel rail fits. This fuel rail has a similar port arrangement as the other two Nissan rails. However, there is no 1/8NPT port on the fuel rail. If a 1/8NPT port is required for a pressure gauge or transducer, Radium Engineering offers a fitting with the provision for this.
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