Awesome work. :icon_tup:

very nice work. i wish i would have done something similar when i had my turbos off...

Actually the air will still flow over. Remember under acceleration, the primary turbo is still providing boost pressure. So no matter what the secondary side will still pressure up even past that divider.

100% agree!

Everyone here (including the OP, at least with how he configured the animation on his drawings) has the wrong idea on the original concept behind inserting a divider into the y-pipe.

The concept is not to gain better primary turbo flow and improve response there; the idea is to improve flow from both turbos into the y-pipe/crossover tube once the secondary transition has occurred. Because both turbos are flowing into the y-pipe junction after transition, a lot turbulence (which hinders airflow) occurs because of the opposing turbos' airflow colliding at that point. The idea is to smooth the airflow into the intake tract, thereby theoretically improving flow (and hence, power) past the transition. Whether it actually accomplishes this to any noticeable extent is, yes, a matter of debate.

Oh yes, and this would theoretically benefit NS twins as well because of this concept.

100% agree with that too. This mod appears to cause a slight lag ( maybe not even noticable) of the primary turbo but yet benefits in the top end. Sounds like a good trade off.

From what I can tell, this would actually benefit a NS setup more so than a S setup...

The Y-Pipe split mod ~
 

Saw it posted as a how to a while ago. Seem's the JDM boys do it too ~

http://page4.auctions.yahoo.co.jp/jp/auction/d73422202

doesnt that mean less volume to allow for air flow?

no, it's less turbulance for the air.

There was a guy who did this mod a few months back. Search and you shall find.

yea kinetic (not right spelling)i believe created this mod

No, he didn't "create" it; the modification was featured in a Japanese magazine some time ago (which he mentions in the very first post).

While the divider appears as if it might "constrict" airflow from either of the turbos (probably what the one post means by "less volume"), the improvement in flow when both turbos are in full function was deemed worth any possible restriction (which would be very small IMHO, because neither turbo really flows that much by itself). For that reason, I don't see why this modification would benefit a NS setup more than a sequential setup, either.

Because, like I said before, the air coming from the primary turbo would have to go over the divider and into the secondary turbo's area. I'm not sure exactly how the airflow would look using arrows or anything. I'm guessing, since the primary turbo obviously doesn't begin to compress until the piping is filled, it would have to fill all of the piping going forward, and then right before it begins to compress, the air would have to creep back into the secondary area. I think this would either cause a lot of turbulence, or just a *slight*, probably unnoticeable delay in response. With a NS setup, they would both be pushing air at the same time anyways, so it wouldn't have the same effect.

This is just an observation, correct me if I am wrong.

The volume into the secondary turbo portion of the y-pipe doesn't change-- that's the important part. The airflow doesn't have to flow "over the divider and into the secondary turbo's area" first before it flows into the y-pipe and crossover tube; all it will do is basically backfill that area once it pressurizes the intake tract, and there won't be any turbulence that would be any worse than that created by having to force the airflow past the open space in the secondary turbo duct if the divider wasn't there. Because the volume is the same, that aspect won't change, so there won't be any delay in response caused by this.

In 1996 (I think??), Mazda engineers (very intelligent engineers) redesigned the y-pipe to flow better. I think it's a fair assumption that they tried a lot of different designs before coming up with the better flowing "efini" y-pipe. I would bet that they (very intelligent engineers) tried a similar design to the one in this thread, and found it to be inferior.

Doesn't the charge control valve stop air creeping into the secondary?

The Charge Control Valve controls the transition from Primary to combined Primary and Secondary Turbocharger operation. When ever the pressure applied to both Chambers of the Charge Control Actuator are equal, the spring force of the Charge Control Actuator will open the Charge Control Valve.

Below 4500 RPM this actuator is ON, (actuator rod pulled in), this closes the valve between the Primary and Secondary Turbochargers. This valve seals the air passage the same way as a throttle butterfly valve.

Yes, the CCV door seals off majority of the secondary turbo portion of the y-pipe, but there is still a small open space in the y-pipe before the door.
It's a fair assumption, but no guarantee. Remember that Mazda was already in financial straights by that time, and the (very intelligent) Mazda engineers were surely constrained by company bean counters in just what improvements they install, much of that in order of importance. Testing costs a lot of time and money, both of which were surely in very short supply to the (very intelligent engineers) at that time. On the flip side, it's also a fair assumption to say that moving the bypass valve tube out of the airflow path in the Efini y-pipe is more of a change that could be done without any testing; it's an easy theoretical idea to smooth the intake tract, just like the divider.
That said, I'm not saying that the y-pipe divider modification is guaranteed to improve power either. I'm only explaining the concept behind it.

Kento,

Sometimes some of these engineers show up for sevenstock. If I go this year, I will try to remember to ask them.

Cool, that'd be great to hear their views.