Fuel Injection: How to Build a Fuel Injection Manifold

Lead Image
  • 4-8 hours
  • Advanced
  • 125-250
What You'll Need
Head flange
Intake runners
Throttle body
Plenum chamber
End plates
Injector bosses
Fuel rail
Hole saws
Drill press
TIG welder
Fuel rail

Fuel injection is a fuel delivery system mostly used in automotive engines for mixing air with fuel. Each fuel injection system is designed and regulated according to the type of fuel it will handle. Fuel injection systems can be used for diesel and gasoline applications. Their effectiveness and performance has made them a preferred replacement for carburetors. Follow these steps to build a fuel injection manifold for your vehicle.

Step 1: Attach the Head Flange

Attach the head flange to the intake runners and plenum chamber. However, before you do this, make holes for the intake runners in the head flange. This can be done with the help of a hole saw. Ensure that the holes are of the right size for the runners. With a drill press, drill bolt holes in the head flange. When this is done, place the intake runners and plenum in the flange and measure it for straightness. Lightly tack weld the pieces together at both sides so that they can still be moved around. When you are sure of the joints, TIG weld all the joints, the throttle body flange and end plate caps. Allow it to air cool.

Step 2: Connect Injector Bosses to Intake Runners

Cut holes in the intake runners. These will allow the injector bosses to poke through. To do this, etch a line across the intake runners where the center of the injectors will be. Then intersect each of these marks with another line through the center of each tube. Punch mark the runners and drill a ¼-inch hole. Use a ½-inch drill and drill straight through. When you have pierced the tubing, lean the drill slowly at a 45 degree angle. This will help to oval the hole of the runners.

Step 3: Join the Bosses to the Injectors

Place the injector bosses over the oval holes. Ensure that there is adequate space around the flange and boss joint so that they can be welded easily. Place the injectors into the fuel rail and slip the bosses over the injectors. Align the assembly together carefully with the injectors exactly in the middle of the holes in the runners. Secure these in position and recheck the assembly.

Step 4: Secure the Manifold with Bolts

Once you are sure of the assembly, tack weld all the bosses in position quickly and lightly. Water quench the tacks or pull the injectors out immediately to prevent them from heat damage. If you are sure that everything is in place, weld the bosses. Ensure that the bosses are welded in straight and at similar depths so that they can be sealed properly. Bolt down the attachment bolts for the manifold and tabs on the fuel rail. A few ¼-inch bolts will be sufficient.

Clean the fuel injection manifold with hot water, soap and lacquer thinner. Finally, powder coat or finish it with a good quality engine enamel.