this mod sounds like the air tornado thing on tv. are there any fuild dynamic scholars in the house? time to apply what you learned. :) help us out here. does it really work? what's the physics behind the two small cross sections as compared to one large one again? what about flow characteristics in a semi circle as compared to a circle? etc, etc.

My point is on the exhaust side of the equation so the laminar/turbulent flow do not apply. My suggestion is merely to separate the exhaust turbines from one another. Since they force compressed gasses against one another, if you could eliminate this reversion at say 60K rpm and up the turbos WOULD produce more boost and much more efficiently since they wouldn't be working against one another.
Art

They'll be working against each other anyway.. You still have to pressurize the entire system before you can build boost. It would eliminate some turbulance down at the Y to maybe ease the transition, but once both turbos are spinning, I can't see how you're flowing any more air..

... which brings me to my idea for the non-seq guys. Why not just block off the primary turbo outlet? It's not pushing boost, all it's doing is providing an alternative path for the secondary air as it spools = more lag. Has anyone tried blocking it off or just putting in a pipe from the 2ndary outlet directly to the x-over pipe?

-pete

YGBSM!

Turbulent BLs would be better anyways because the flow would stay attached longer around sharp turns. Thats why golf balls are dimpled....

Been smoking again? I don't think I understand what you are saying. To me it sounds like you are saying to kill the primary turbo. One turbo only?

Been smoking? no. Do you have any idea at all how non-seq works?

Pay attention smartass:
Non-seq doesn't use the primary turbo at all , by locking in the turbo control rod and leaving the CCV wide open you've just told the primary to fuck off. Let's take this point by point:

1. The turbo control arm mod:
This directs most of the exhaust gas away from the primary. Notice the change in exhaust pitch with NS? That's the less backpressure of the secondary. Notice the missing sound of a primary spinning up with NS?

2. The CCV mod:
This makes the (very slowly) spinning primary try to pressurize an even slower spinning secondary compressor outlet stage. The end result is no boost until the secondary can reverse this flow. Even if the primary had full exhaust (which it DOESN'T) it still couldn't boost because it would just try harder to backspin the secondary.

3. Pre-control mod: (optional I know) This directs yet more exhaust away from the primary turbine see (1).

IDIOTS VERSION: Non sequential is just secondary mode for the turbos. You are not getting any useful flow out of the primary turbo. That's why you get stuff all power below 4500 in 1st 4000 in 2nd and 3750 in 3rd.

I'm happy to draw you a picture if you like.

Now as to what I was saying - When the turbos are in secondary mode, the only thing stopping the secondary compressor from forcing air into the primary is the fact that the primary can still have +ve flow until redline. It cannot flow as much as the secondary and as a result causes the secondary to bleed off pressure - losing you power. If you bypassed the primary altogether - I cant see why you shouldnt get the performance of a reasonably sized single.


-pete

Uhh.. what?

Let me get this straight.. You're trying to say that the secondary turbo makes all the power after the transition? You do understand that it's sized exactly the same as the primary turbo, don't you? It's no bigger at all. So why would just spinning the secondary take longer to spool than just spinning the primary, genius? Why would spinning just the secondary make more power than the primary? Hmmm... Haven't thought this out, have you?

NON-seq runs the turbos together. THAT's why you don't hear just the primary spooling. Because they're BOTH spooling. But please, draw us a picture. I'm curious to see exactly how your car runs.. do you even have an FD?

Turbine sizes:
-------------------------------------
Primary 51mm (50mm for 99+)
Secondary 57mm

LOL I can just see you fuming away there. That makes it all worth it :)

-pete

LOL!

Hmmm, where did you happen to run across that info???

If your talking about US 93-95 FD twins your info is wrong. The 2 cartridges are completely identicle

You sure a bloken apex seal didnt go thru your pri and chew about 6mm off it lol

STEPHEN

Pete, don't get all defensive or anything, butyou have got that all wrong. When you go nonsequential you are simply taking out (or opening up) the doors that allow the turbos to spool independently. The stock sequential system at 4,500+ rpm, and a nonsequential system at any rpm are simply dividing the exhaust gases (relatively) equally to both turbos. The reason it takes so long to spool the turbos with nonsequentil is because you have twice the mass to rotate (i.e. two turbos instead of one). There is no need for all the hostility. P.S. the turbos are the same size.

I guess he was smoking. Don't worry; I felt the same way when I learned that you don't use an apostrophe "s" after "it" to convey possession. I also felt stupid, but I got over it.

:rofl::rofl::rofl:

That was fantastic...

Wow ... I was really worried about my understanding of the FD for a minute.

Pete,

Definitions:

Sequential - One at a time, Take your turn children!
Non-Sequential - Both at the same time, every man for himself!

During sequential mode, the low volume of exhaust at lower RPM's is enough to boost one small turbo efficiently but not one large or two small ones at the same time. Since the primary turbo is small, at larger volumes of exhaust flow at higher RPM's, it becomes inefficient and high back pressure on the exhaust would result. Now comes the little flapper doohickey bypass. It allows some of the exhaust pressure to pre-spin the second turbo and allow it to reach close to operating speeds and temperatures faster. Now open up the full flow to the second turbo, your boost drops. This is because your exhaust volume is the same at this point, but now your flow goes through twice the volume as before because the second turbo flap is opened and taking about 1/2 the flow and energy from the exhaust stream. Boost increases again as the RPM's increase and the exhaust volume increases until the wastegate says: "Whoa dude, too much boost, dumpin' excess now!"

Non sequential allows all of the exhaust gas to flow through both turbos at the same time. Thus you have turbo lag (low RPM's not enough volume to spin both turbos efficiently) and late power band boost.

Remember, the reason that Mazda went with two turbos to begin with was to nearly reduce or eliminate turbo lag. This is what they advertised. Otherwise, they would just go with a big single and have a more dependable car.

Now today's technology is allowing better and more efficient turbo boost patterns and giving the RX7 different options for single turbo upgrades.

Tim

Um, no offense, but....was there a reason for resurrecting this thread by replying to a post nearly a year old?

Kento,

It's not a late reply, he just types slow.

Why does it matter how old the post is?

Yes,

I did a search, found this, felt I had something to contribute, answered and never checked the thread date.

MODERATORS should lock all threads that have had no posts in 30 days. If someone want's to open it back up, they would need to repost with a reference to the original. I have thought this all along, but never voiced my opinion about it.

Besides that, I was going to write a 5 page dissertation about laminar versus fluid flow since most people have it wrong, but I will let that up to another aerospace engineer to correct.

Tim

Tim

Tim, Very nice definitions and discussion as to how the turbos operate. For us non-engineers we would love to hear the "laminar vs. fluid" dissertation when time permits.

Paul

I like this mod - it just makes Ghetto sense!

I'm going to use a band saw to cut the entire pipe in equal halves and then tack weld in a divider to COMPLETELY separate the sides, then weld the pieces back together. I plan on using a piece of metal for the divider roughly the same width as the band saw blade in order to maintain the overall dimensions.

Hell, while there, might as well smooth the interior of the pipe - can't hurt!

Before I start welding, does anyone have a guess as to what type of metal the y-pipe is cast from?

I GOT IT!!!!

GET THE TORNADO!!!

Sorry for shouting guys, I was excited.