I have what is said to be a street ported 83 12a with a Racing Beat intake supporting an Edelbrock 4 barrel. Switching to a Mikuni side draft. When I pulled the RB intake I noted that the center ports on the intake and the engine were about a half inch taller than the gasket that was used, causing apparently restricted flow. The gasket perfectly fits the intake for the Mikuni. Looking at the MAZDATRIX site I see a gasket with taller center ports openings for an earlier engine, but it doesn't have the rectangular hole beneath the center ports that are on my engine. The engine center ports appear to have the rough surface of a casting, so it doesn't look like they've been opened up? Doesn't make sense. Can I just run the Mikuni manifold with the shorter ports or should I port it out to the dimenson of the ports on the engine and trim a new gasket to fit?

 

Thats actually pretty common. Most will tell you port matching is not a good idea.

 

Just run the intake with the short ports and you will be fine.

 

Do not port match the intake to the block, it reduces air flow/velocity in the long run, not a good thing. At most, I would ease/round the edge on the intake for a smoother transition, but nothing more than that.

 

Thanks for the replies. Consensus seems to be run the shorter manifold ports which match the gasket as is. I read the Yaw article on flow which advised not matching the intake ports to the engine. I'm just surprised that the difference between the manifold and the engine are so extreme.