I've been around rotaries for some time now and haven't seen too many aftermarket intake manifolds. My experience with every other engine I've worked on has shown that the difference they can make is quite significant. One thing the plenum needs is volume, and the stock 13B plenum has none.
In our spare time we'e built a manifold that takes care of a few of the shortcomings... has volume, larger ports, less restrictive flow path, and utlilizes perhaps the most popular throttle body upgrade (Q45). This also keeps the TB in the same location, allowing for the use of the existing IC piping.
There are a few members on here that have shown great results using custom intake manifolds, and as no one makes once, so why not...

 

That's really nice...

 

I love shiny.....

 

Dyno results? Any factual comparisons you can make over the factory? You setting up a group buy? This is an idea that would sell well if the data is there to back it up.

 

looks like you cut a 13b-rew manifold in half and attached a plenum similar to the 13b-re manifolds.

13b-re manifold:


is your new manifold made from scratch or does it use a 13b-rew 'donor' - i would guess that you used 1/2 of a 13b-rew uim because even though its polished you can still see some of the original texture on the rew half.

 

I thought the REW UIM was really pretty good, I've seen a few one-offs that really didn't show much of a power difference.

If you remember a while back, Ernie T had a really nice custom plenum and it didn't really do anything for him (and he's pushing lots of power where it would make a difference if it could).

But who knows, maybe this one will get the job done.

 

The manifold was constucted using a section of the uppe intake manifold runners. A pipe was then welded to these runners and cut in half. All the ports were opened up and bellmouthed for better flow. The pipe was then welded back together after all the porting was completed. Working on plans to do a back to back dyno with it. Also keep in mind that dyno numbers do not always show the full story on a manifold. The additional plenum volume can also be nice on the track where reserve air is needed for quick throttle modulation. Here is a picture of the inside of the manifold to see the porting. Sorry for the poor quality. Also attached are other manifolds that we have done. Its not like I am making my first one.

 

ah i knew it!

again, very nice work. sexy mirror finish!

 

Here is another one that we did for a 2jz quite a few years back and a toyota v8. We've been making intake manifolds for the past 7 years mostly for nissan, toyota, lexus, and now mazda.

 

Beautiful.

 

looks great but looks more suited to a 4-cyl or a high rpm race 13B...

In stock form the primary ports and primary single throttle work for lower rpm intake charge velocity, the secondary throttle remains closed while the secondary ports are "connected" through the secondary manifold runners and providing a resonant volume (at least this is the intention) to help have better throttle response and low end torque; at higher rpms the secondaries provide additional flow. Having all four ports like that will kill low rpm charge velocity and any already low low-rpm response and torque won't it?

 

I understand your point and it makes a good bit of sense. The manifold will have to tested to know for sure, but the goal of this peice would be to increase top end power, lets face it the rotary is not made for low end torque so if a sacrifice is made there I would not think it would be a big deal as out motors are not doing much down there anyway.