In the late 80's, an Koenig (Ferrari tuner) made a QUAD turbo Testarossa. For this vehicle, they ran 2 small turbos sequentially into 2 larger turbos, each pair operating on one bank of the V12.

 

Apparently the Mkiv supra TT does use a sequential TT setup: from mkiv.com faqs:
turbo system
1. how does the ssts (sequential twin-turbo setup) work?
first off, the is no #2 wastegate. there is only one wastegate and it comes off the #1 turbo because that turbo is always on line, therefore you always have a wastegate. there are 4 sets of vsv's, actuators, and control valves for the sequential turbo system. each vsv is simply a solenoid that is either 100% open or closed, allowing manifold pressure to pressurize the different actuators that open/close the four different valves.
wastegate: when the manifold reaches 11#'s of boost, the ecu sends a signal to the wastegate vsv, that allows manifold pressure to build in the wastegate actuator which opens the wastegate.
exhaust gas bypass valve (ebv): somewhere around 3500 rpm, the ecu sends a signal to the exhaust gas bypass valve vsv, which allows manifold pressure to build in the exhaust gas bypass valve actuator which opens the bypass valve. this is a small opening inside the #2 turbine housing which allows some exhaust gas to go through the turbine of the #2 turbo which makes it start spinning, and dumps the exhaust gas out the exhaust piping coming off of #1 turbo. since it is a small amount of exhaust gas, it pre-spools the turbo and does not get it up to full operating speeds. this will smooth out the transition from 1 to 2 turbos. This valve is similar to a wastegate in design, but is located after the turbine wheel instead of in front of the turbine wheel like a wastegate would be. this is not a wastegate!
exhaust gas control valve (egcv): this valve is located in the exhaust piping downstream of the #2 turbo. when this valve is closed, all exhaust gas must go through the #1 turbine wheel to get out through the rest of the exhaust system. at around 4000 rpm, the ecu sends a signal to the exhaust gas control valve vsv, which allows manifold pressure to build in the exhaust gas control valve actuator which opens the control valve. this allows exhaust gas to go through #2 turbo and out the exhaust system which brings the #2 turbo up to full operating speed.
intake air control valve (iacv): this valve is located in the intake tract coming off of #2 turbo. it is closed below 4000 rpm so that boost pressure coming off of #1 turbo cannot backup through the #2 turbo and back out the air cleaner/suction of #1 turbo. there is also a 1 way reed valve within the same housing of the intake air control valve. as the #2 turbo starts to pre-spin at 3500 rpm, it will build some boost. if it builds enough boost, it will open the 1 way reed valve to allow this boost into the intake tract to join with the discharge boost pressure coming off of #1 turbo. at somewhere over 4000 rpm, the ECU sends a signal to the intake air control valve vsv, which allows manifold pressure to build in the intake air control valve actuator which opens the control valve. this allows the full boost pressure coming off #2 turbo to join in with that coming from #1 turbo and you are now fully on line. Usually, the exhaust gas control valve will open first, which gets the #2 turbo spinning at full rate so that it is building good boost before the intake air control valve opens, allowing this boost to join in with that coming off #1 turbo. if the intake air control valve opens before the exhaust gas control valve, the boost pressure coming off #1 turbo will go backwards through #2 turbo, spinning it backwards if there isn't sufficient exhaust energy to keep it spinning forward. when the exhaust gas control valve opens, and the #2 turbo has to reverse the direction of the spin. this is a tremendous strain on the turbo shaft and bearings. if the sequential operation is not a well orchestrated symphony of motion, it is easy to see how the #2 can be prone to failure. for an alternate explanation including diagrams, see the new car features section. the appropriate pages are 91-95.



So, from this infromation, combined with previous knowledge... maybe V engines use Twin Turbos that run at the same time, while inline 6s use a sequentila Twin Turbo setup.

 

being a twin turbo 300zx owner I was going to jump in on this thread and clear up alot of stuff. However, you folks handled that pretty well. Bottom line is this. The 350z is one beautiful car. I am in love with the silverstone and I will purchase one in time to come. However, if nismo,greddy, hks , or whoever offer forced induction, GO FOR IT! Also, for you folks that are in the bay area and never rode in a TTZ Myself or Kyle would be glad to give you a ride and introduce you to the powers of the boost. If there is another meet at strickly Z and we are there. just ask and I am sure we will oblige you...

 

That's a damn good looking TTZ man.

 

Positive proof that the Italians invented spaghetti, Not the Chinese!

Dead

 

The gray/dark silver seems to be the best color, imo, on the Zs throughout the generations. I had an NA Z31 that was also dark gray. It looks really good on your Z32, and SS looks really good on the Z33!

 

I would like to see a biturbo configuration designed for the Z. I think a t32 sized turbo being powered by each cylinder bank would make for an interesting torque curve and nice power up top.

 

THere are some in the works right now. Greddy has something going on, and I think one other company, but I don't remember which.

 

Twin turbo versus single turbo, one isn't necessaily "better" than the other. Rather, it depends on the application and the power goal. A single turbo kit, however, is usually less expensive, because it tends to require less parts (including one less turbo).

A single turbo can have less lag than a twin turbo and vice versa. Once again, it depends on the size of the turbo, the trim of the turbo, the qualities of the turbo (variable area turbine nozzle, ball bearing(s), aerodynamics of the compressor wheel, etc...)

I have twin aerocharger turbos on my Mr2. These twin turbos are running parallel and are being pushed by only 2.0 liters of displacement. However, there isn't a one single turbo kit on the Mr2 that has more throttle response, less lag threshold (initial lag), and lag while spooling up than my car. This is due to the VATN system and the fact that my turbos have ball bearings. Hence, I can get full boost at around 2800rpms, when most single turbo kits that can put out the same amount of power at the same boost level as my setup get full boost around 4000rpms.

However, MIKV Supras come from the factory with twin Toyota C12b turbos running sequentially. When Supras go single, most of them decrease lag, but it really depends what size turbo you go with. There are various reasons for this. For one, when one puts a single turbo kit on, they tend to do other mods that help the turbo breathe better, such as adding a downpipe, removing the cats and adding a performance exhaust. Second of all, the aftermarket turbo itself may be a more performance oriented turbo. The compressor wheel may have better aerodynamics, it may be using ball bearings to help spool up, etc... Lastly, you are harnesses 3.0 liters of displacement to push one turbo rather than two.

Then again, some Supras go with twin turbo kit upgrades such as the HKS GT series upgrades where they may use two Gt25 or Gt28 turbos. The HKS GT series turbos is made by Garrett and is part of their new line of Ballistic turbos. Updated compressor wheels and dual ball bearings paired up with a nice combination of a small turbine housing, and a decent szed compressor stage makes this twin turbo setup match the lag of a single turbo setup. Like I said before, it really depends on the application.

Power is determined more on the efficiency of the turbo than on whether you are going with a twin turbo or not. If I am aiming for 1000 horsepower, it might be better for me to use two turbos capable of 500hp each rather than one turbo capable of 1000 horsepower. Using one turbo to achive that number would require me to be boosting a lot. Depeding on the efficiency of the turbo, this might be out of its efficiency range and create more heat. Not only is hot air less dense than cold air (thus less power), but it can cause heat soak and also increase the chance of detonation. It might be better in that instance to pick two turbos that hit 500hp in their efficiency range.

Likewise, If I wanted to hit about 400rwhp on my Mr2, I would better going with something like a Gt3037 single turbo rather than my twin turbo setup, since at those power levels, that turbo is better suited.

Twin turbos can be run in parallel or sequentially as people have mentioned before. Sequential setups are good in theory, however, are complicated in practice. Look at how much trouble Mazda had to go through to make it work on the Fd3s Rx-7. To this day most Rx-7 owners still have boost problems since the vacuum hoses leak and premature from the heat of the rotary engine. Toyota did a better job, however, the second turbo kicking in puts a lot of stress on it and it was suceptible to 2nd turbo failure. Most aftermarket kits just run the turbos in parallel, to avod the complexity. If the turbos are sized correctly, it will have comparable lag anyways. Moreover, turbs running parallel actually are more predictable on the track. Sometimes the driver can spin out when the second turbo kicks in on the sequential turbo. What is more is that sometimes there is a huge dip in the power band during the transition from single to twin turbo.

Finally, whether going twin or single turbo depends on your engine setup. It is easier to go twin turbo on a V setup. However, with long piping you can make a single turbo happen.

The bottom line for most people is that a sigle turbo setup is usually less expensive, since you deal with at the very lest one less turbo. Moreover, the single turbo kit can perform just as well as the twin turbo kit if size and trim was selected properly for the application.