Hey guys,

I started reading this thread on Supra forums and it got me thinking. First, here is the thread:
http://supraforums.com/forum/showthr...hreadid=156380
*Edit: It gets REALLY interesting after the second page. Gets very technical, first page or two is mostly BS. But in the later pages you read of a guy developing a sequential system.

It mentions the Porsche 959 in there, and I also know that Porsche has been turbo'ing cars before I was born. Also, Porsche enthusiasts seem to be very knowlegable people so that is what brought me here.

Did the 959 or any other previous P-cars use sequential turbocharging? I know the 996 is a true twin turbo setup (both turbos are same size and are both constantly spooling). I know Audi also uses the same philosophy in the S4, RS4 and RS6 (biturbo).

A sequential setup would be where one turbo is constantly spooling, and then a second one turns "on" (begins spooling / producing boost). Adding to the total boost.

In this thread, however, they attempt to use two different sized turbos. And then the same discussion comes in. When the bigger one begins to produce boost, should the smaller be shut off? Will the smaller overspin if it isn't shut-off? Should both turbos be constantly spooling at higher RPMs?

It is VERY interesting stuff IMO, and I was wondering if this sort of thing has been done before. I know sequential turbochargers has been done (in the stock Supra, where both turbos are the same size). However I've never heard of a sequential setup with different sized turbos? Also, did Porsche ever have sequential setups?

Discuss...

 

Hi. In 1985 Porsche's Group B 959 sports racer had sequential
turbos. Yes, the smaller turbo must be shut down at higher RPMs.
It is the control and proportioning of the intake flow that makes
a sequential turbo setup complicated.
Joe

 

"Discuss." LOL
Feels like a college essay exam....

 

from my knowledge sequential turbos are usually two turbos of different sizes usually one that is (primary) turbo and (secondary) turbo.. the concept of this is to virtually have no turbo lag whatsoever, basically using te samller turbo to spool up quicker and when the smaller one tops off have the bigger one start spooling up..

people usually call a true twin turboa sequential turbo.. while the true twin turbo has two exact same turbo's connected to the manifold i.e. Z32 chassis of the nissan 300zx and the 1jZGTE motor that was available for the 89-91 toyota supra for the japanese market, which had two c-12 ceramic turbos, and the old 1ggteU motor on the 87-88 toyota supra turbo.


sorry for the tangent the late body rx-7 came in a sequential turbo format also,

but peopel usually excange the setup for a big A$$ turbo instead, junking the sequential setup for the big boy turbos seen in hks, greddy cars..

i hoep this info helps..

 

Alright, that answers most my questions.


Basically, the sequential turbo system has been done with two different sized turbos, that's very interesting. However, they all seem to be using one turbo or the other. I believe in that Supra thread they plan on using the smaller all the time, and the bigger one at higher RPMs. That may be a first, but from what i've read, who knows if it will work and if it does, will it be efficient and useful?

 

It will work if the plumbing/control ensures the smaller turbo
never gets too much exhaust input to push it beyond it's
efficiency region, and if the pressure downstream of the turbos
is retained and not leaked back through the non-running
big turbo at low RPMs/exhaust flows. If one turbo is producing
X psi of boost and the other is producing less, the higher boost
is in effect reverse-driving the other. (I'm guessing)
Joe

 

In a prior 'turbo' thread I brought up the topic of the "Variable Area Turbine Nozzle" (VATN) Turbo. In essence it is a big turbo that can opperate as a small turbo buy altering the velocity of the exhaust gas in the turbine (hot) side. Velocity of the exhaust can be increased at low speeds/rpm by changing the angle of the 'vanes' in the turbine side. Appearantly, you can have a big turbo that can act as a small turbo at low RPM's.

"The response time of the VATN is approximately half that of the standard turbo."

quoted from MAXIMUM BOOST - Designing, Testing and Installing Turbocharger Systemd by Corky Bell.

To me, this technically sounds like the best of all worlds. Anyone know why it hasn't been developed to the point where it rivals sequential or twin turbo set-ups?

Mike

 

Kevin -> seeing as you are "THE" Turbo Guy, it would be timely for you to make some very technical "Turbo Guy" comment.

 

i have that book at my home, (maximum boost) i even had the chance to talk to corky bell when i was in the process of installing a T04E on my toyota supra, very help ful gentleman

 

I guess only the future can tell. But cars are constantly becoming more efficient and if manufacturers want to continue doing so, they will need to explore this technology.

I like a sequential setup but you are always adding weight, VATN seems like the best but it is also the most complex, and thus has the greatest chance of failure.

Also, I know Honda makes a diesel civic in europe with a VATN, so its already being produced.

 

I read somewhere that they were having the computer periodically open and close the movable nozzles to sweep the carbon off. Supposedly this resolved the sticking problem. I'm sure we'll see variable nozzles on future Porsches, diesel Mercedes, etc. They're also working on electric motor assist to get the impeller spinning.

 

Thanks for the input Turbo Meister!