There are some mistakes on the intake, and i have fixed them.

The holes in the spacer plate are smaller than the carb and the intake. The primairy holes are 24mm, but the carb and intake are 28mm. The secondary holes are 32mm, but the carb and intake are 34mm.
The one on the right is made bigger to match the carb and intake.




There is a channel between the two primairies. Horrible aerodynamic airflow.





I binned the spacer, and made my own. (ignore the wedge shape). Just holes, no channel between the primairies.




The channel between the primairies is however needed. I made it by making a channel in the intake.




There are channels between the primairies and secondaries. These channels are edgy and square. Not aerodynamic at all. I don't see the benefit to join primair and secondair. So i closed the channels.




Now the intake have separated primair / secondair runners. Both with aerodynamic runners, without horrible square edgy connection channels.

And one rotor is properly feeded by 2 primairies. The 2 primair runners are now properly aerodynamic joined, instead of horrible square edgy connection channels.



I haven't dyno'ed it yet, but the primairies are feeling much stronger.
But i don't notice difference on the secondaries.
And it is 10% more fuel efficient

 

The stock layout of the manifold and spacer was for gas mileage on a stock port 12A and emissions prposes. We all want more power. Maybe we can find it in the intake manifold.

I think you did all of that with good intentions, but let me clarify some of it for you.

The stock spacer provides an anti-reversion lip, which you eliminated with your new spacer.

The stock channels connecting primary to secondary don't need to be aerodynamic to flow well, and they are a good idea to keep. I've experimented with both channeled and separate runner and determined channels perform over all better. I'd keep them if I were you.

The stock spacer is phenolic which has some heat insulation properies. Yours is metal.

Did you block off the coolant ports and the ACV port? Oh wait, you've got a 79 manifold there that doesn't cover over the ACV port. Never mind. But you still should block off the coolant holes with 20mm freeze plugs if you haven't yet.

When I was experimenting without any spacer at all, just using short carb mount studs and a shorter OMP lifting rod, I didn't add a small channel under the primaries and just let the stock channel under the carb handle that. The results at idle weren't much different. But I'm willing to give it another go when I swap back to NA. It's currently got a turbo with a phenolic spacer and does well (until it sees boost whioch upsets the carb, but that's a whole other thread so I won't muck up yours with it any further).

So in the end Mazda didn't make any mistakes with the intake. What they did was all calculated carefully for reasons of emissions and fuel mileage. But there are ways to get the intake manifold flowing greater than stock, but I don't think blocking off the channels was the right way. Perhaps doing what Sterling and Glazedham42 did by increasing the width of the channels and smoothing the edges is the way to go. Oh and keeping the phenolic spacer. But I understand your car isn't a a Mazda and some of the carb angles might be corrected with a wedge shaped spacer - it just should have been a wedge shaped phenolic, like what Mazda did on the RX-2 Nikki setups.

 

I think Jeff said what I was going to say but there are different diameters on purpose. It's basically part of "tuning the intake" tract if you will... It helps to keep the glow going in the correct direction. Similar idea as the intake in the lemans 787b four rotor.. Although that had an intake that changed length via actuator with load and rpm this is purposely done to make "sound/pressure waves" hit that lip and go back toward the engine... Let's see some before and after dyno vids

 

Well, i am happy with the results. It is more powerfull on the primairies, and more fuel efficient.

This is without increasing the primairy venturies. Maybe that's the next stage.

I also want to separate the air intake. A short circuit to the secondairies, and a long circuit to the primairies. Some kind of a frankenstein air filter pipe work.
And then dyno it!


This is from last year dyno, without all these mods.