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6 Port Manifold on 4 Port Engine

The stock 13B 6 port lower intake manifold is a useful starting point for making your own low profile manifold. It is a little heavy compared to fabricating one from scratch out of aluminum plate and tubing but it has the advantage of being already there and comes "free" with the engine. After removing the unnecessary EGR valve and secondary port valve actuators, it weighs about 6.5 pounds and can be lightened further by removing the outer EGR jacket with a die grinder. The holes for the rotary valve actuator shafts were used for the secondary injector mounting points. Details on converting the lower manifold for a low profile manifold can be found in "The Mazda Papers".

When I replaced my old 6 port engine with a 4 port engine about 400 hours ago, I was forced to either make a new lower manifold from scratch or modify the 6 port manifold I had been using. The stock 4 port lower manifold is much taller than the 6 port version and does not have a convenient place to mount the injectors. Since I enjoy flying more than endless hours of fabricating, I decided to modify the old 6 port manifold.

Shown below is the face of the 6 port manifold which mates to the engine block.

On the left side you can see how I removed the web between the two secondary ports using a die grinder. On the right side you can see how epoxy putty was used to fill the top port area and match it up with the 4 port engine. The odd shaped openings below the outside ports are EGR passages. They are plugged with epoxy putty.