Fuel Rail Adapter - Making an Adapter for Non-Metric Thread Fuel Pressure Gauges
Two fabrication methods for making a metric-to-SAE adapter that allows a 1/4-inch flare fuel pressure gauge to connect to the 12 mm × 1.5 thread 944 fuel rail end cap.
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Introduction
If you want to check fuel pressure on a 944 with a standard 0–100 psi gauge fitted with a 1/4" flare fitting, you need a metric-to-SAE adapter to connect to the 12 mm × 1.5 thread fuel rail end cap. Two fabrication methods are described below — choose the one that best matches your tools and available materials.
Tools and Materials
Note: When sourcing brass fittings, you may find a 1/4" NPT-to-1/4" flare fitting more readily available than a 1/8" NPT version. If so, use a 1/4" NPT tap instead of a 1/8" NPT tap. The 1/8" NPT thread is specified here because its smaller diameter makes it easier to see the thread transition when drilling halfway through each side of the adapter.
Option 1:
- Spare fuel rail cap nut, Porsche P/N 928 110 475 01
- 1/8" NPT tap
- Brass male-to-male fitting (1/8" NPT to 1/4" flare)
- Teflon thread tape
Option 2:
- One piece of round stock, aluminum or mild steel, 7/8"–1" diameter, approximately 1" long
- 1/8" NPT tap
- 12 mm × 1.5 tap
- Brass male-to-male fitting (1/8" NPT to 1/4" flare)
- Teflon thread tape
Option 1 — Modified Fuel Rail Cap Nut
- Obtain a spare fuel rail cap nut (Porsche P/N 928 110 475 01).
- Drill and tap a 1/8" NPT thread hole in the center of the cap.
- Apply Teflon thread tape to the brass male-to-male fitting and thread it into the cap nut.
Option 2 — Machined Round Stock Adapter
- Center punch a starting indent in the middle of the round stock and drill a small pilot hole all the way through.
- From one end, drill approximately halfway through the stock using a 10 mm (or 13/32") drill bit.
- Thread this opening with the 12 mm × 1.5 pitch tap.
- From the other end, drill approximately halfway through using an 11/32" drill bit.
- Thread this opening with the 1/8" NPT tap.
- Obtain a 1/8" NPT to 1/4" flare (male-to-male) brass fitting and thread it into the adapter.
- Optionally, mill or file flats on opposite sides of the adapter to allow tightening with a 17 mm wrench.