This is a brief "How-to" article for modifying an aluminium intake manifold for electronic fuel injection.
* First decide if it is cheaper to purchase a manifold that is ready to accept injectors. Don't forget to take into account the time (labour & difficulty) and if you have access to the tools (or a friends workshop
) to carry out the required machining.
* If the manifold is thick enough you may be able to machine the injector pockets directly into the manifold. If it is not thick enough weld on extra material or machine injector pockets to weld in.
* The injector pockets can be made on a lathe,
The dimensions shown here can be adjusted to suit different applications. These were to suit GM LS1 injectors.
The important dimension is the O-ring seal (diameter 14.0mm in the diagram below) this must provide the correct amount of crush to seal the injector & manifold. Debur the edge after drilling and use silicon o-ring lube when fitting the injectors to prevent damage to the o-ring.
*The manifold can then be machined to accept the pockets (or machined dirrectly if enough metal has been added by welding).
Injectors are usually mounted as close to the head as possible and angled to spray at the back of the intake valve(s). This gives good idle and economy. Race cars sometimes have the injectors mounted at the top of the intake runner to give better top-end performance.
Note the angle of the hole relative to the runner airflow.
Try to keep all the injector pockets at the same height (this will make it easier to manufacture the fuel rails).
As you can see the counterbore has cut into the intake runner. This is ok as the injector pockets will be welded around the outside to seal and the inside of the runner can be ground out afterwards.
The pockets in place ready for welding to finish the job.
My appologies for the images, I only had the camera phone.