Other than fly cutting the flange mating surface, boring the tube
counterbores and drilling the bolt holes, will any additional material be
removed to take some of the bulk out of it?
...Chrissi

The amount you cut off to save weight depends on what
year Mazda engine you have. Bolt holes are in different
locations for 93 and later engines. This is the reason it 
was done this way. A drill and a hacksaw can be used to 
cut material off you don't need.

Boring the counter bores is optional. You could just tig
weld on the pipe or tubing bends. One of the reasons
this manifold is only 90 degrees is so it can be ported with
a die grinder to accommodate those people that are porting 
their engines and would like to use larger dia. runners. The 93 
and later ports are larger than the 93 and earlier of course. 
It is set up for 1-1/2 and 1-1/4 pipe Sched 40 right at the moment 
because the bends are half the cost of tubing bends. .065 wall 
2 inch tubing is pretty close to that for the large size.

You could also use composite runners from here on out since
heat from the exhaust and a turbo if used is less of an issue. 
A flange can be molded on the composite
runners with four or six 6-32 or 8-32  hold down screws.
Drill and tap the top of the manifold for the screws.

I tried to design this manifold for maximum flexibility.

Paul Lamar
 
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