Okay, so I got my 1st FD today. HORAH!!!!! It's a 93' Touringm but my main question lays towards the sequntial Twin Turbo set up.....

The 10-8-10 Deal...... does this mean that the first turbo spools to 10psi and then there's a 2 psi drop when the second turbo spools up, and then boost stops at 10 psi again? if so what's the purpose for the secondary turbine? also, going from a sequntial setup to a standard duel set-up, what are the major differences? thanx and also if you can tell me what to search under, you don't need to waste time answering my ? thanx ya'll

 

The exhaust bleeds off to pre-spool the secondary turbine as the first one is running out of capacity. The secondary turbo comes on line and the boost dips a bit.

 

The benefits of having the twins from my understanding is that even though it is running the same PSI as on the primary, the intake temps drop dramatically because the exhaust is routed through both turbos, instead of just the primary. As for the differences in the sequential system vs. a parallel set up, it seems that the reason people do the non-sequential swap is to get away from the problematic sequential system. I personally love the sequential response, theres no subsitute for the quick spooling power. But the parallel set up tends to have less problems...

 

ahhh..... so the stock boost setting is 10psi at full then? if so, then when increasing boost, is there 2 wastegates, or 1 that controls both turbines?

 

http://www.autosportracetech.com/RX-7/rx7stuff.htm

Good luck with your FD, this should get you started.

 

the reason two turbos are employed instead of one is for spool. one small turbo spools up for the first half of the rpm band, then one turbo isnt enough anymore so another on ekicks in to pick up the slack. im sure temperature is adversely affected by this, but this is a side issue. the purpose is to get instant boost.

 

There is one wastegate to control both. However, there is a thing that is really similar to a wastegate that bleeds exhaust off during primary-only operation and pre-spools the secondary turbo. But when both turbos are running, the wastegate-like-pre-spool-gate has no effect on boost level -- the single wastegate is the only way to regulate the boost level.

One of the stock turbos could not provide enough flow to make 10 psi at redline. And it would be way out of its efficiency range long before that, raising the intake temps to dangerous levels. So, with the sequential system you can have one small turbo run at low RPM for good response, and then bring a second turbo in when the first one starts to run out of flow. The two turbos are the same size, and both of the turbos are in use above 4500 RPM (aka "the transition") when you are under boost.

-Max

 

thanx ya'll, good explanations from everyone, IT MAKES SENSE!!!! WOO HOO!!!

 

just so you know... do NOT increase the boost without an ECU. our stock ECUs are NOT mapped for any higher boost than 10 psi. you can do flow mods like intake/dp/cat back, but keep the boost in check. a boost gage is a huge reliability mod on these cars. look out for spiking on transition instead of a dip, caused by too much prespool without enough wg open in primary operation.

 

This may be too late, but I have some extra turbo info at
www.davidgeesaman.com.

 

^Just scanning some of the topics and looks like very good info, especially on the hose job, which I'm about to undertake. Thanks.

 

I thought that the wastegate was entirely shut until 4500. I would check on my sources, but I dont have them with me. Could you elaborate on wg-pc door operation or point a source?

[edit] Check the service highlights, page F22. It indicates the wastegate stays shut until midrange. (its on my site)

Dave

 

Dave,

I believe that max's post says exactly what your write up says - prespool door regulates boost below transistion and wastegate regulates boost after transition. That is what I got from max's post when I read it. You may have misunderstood because he says the prespool door is "wastegate-like".

 

This is also the reason that the 99 primary turbo is known for "running out of breath" since the 99 turbos are a true sequential system (first turbo is smaller then the second). The primary turbo simply can't provide the flow the engine needs at higher rpms. If you look at a dyno graph for a 7 equipped with the 99 turbos you will see a slight loss in power before the transition begins.

 

screw it all. throw it away and get a smaller size single. you won't miss the sequential setup.

 

You sure about that?

 

Not positive, but I seem to remember reading all the info I previously posted in an old thread. If someone knows better please correct me.

 

Sequential refers to the way the turbos are staged, not the size.

93+ RX-7s are all factory *TRUE* sequential twin turbos.

 

You're wrong. Both turbos are the same size. The Cosmo used different size turbos for its sequential setup, not the RX-7.

 

That's most likely where I remembered it from. Thanks for clearing that up as I was searching through the 99 spec twins threads looking for the proof to back up my claim and was coming up empty.

However, I am almost certain I remember reading a thread of someone that dyno'd his 99 spec twins and it clearly showed his power curve leveling off before transition and the explanation was that the primary on the 99 twins "runs out of breath" earlier then the previous turbos. Of course it was in the 3rd gen dyno section which seems to have been cleaned up recently.

I think you know what I meant

 

No, I don't think I did.

I *thought* you said that the 93-98 weren't true sequential turbos, which I thought I politely corrected.

 

Just to clarify; in my original post I wrote "the 99 turbos are a true sequential system (first turbo is smaller then the second)." The section in parenthesis is what I was using as an interpretation of what I meant by "true sequential system." I wasn't saying by any means that the pre 99 turbo systems weren't sequential turbos, but was indicating that my definition of a "true" sequential turbocharger system would be to have a smaller primary turbo for good low end response and a larger secondary turbo for greater flow on top end. I realize I should have made my initial post clearer and checked my sources before posting erroneous info.

 

Youre right - my bad. Max knows his stuff, so I read it twice, but apparently I still didn't see it correctly.

Dave