dual stage turbos

Post by **dreamsOfSkylines** » Thu Feb 20, 2003 9:04 pm

I know the porsche 959 had them, and maybe the late model RX-7s. How do they work? My understanding is you had one smaller turbo for low revs and then one big one for high revs. But how would you switch between the two, redericting exhaust seems inpractical. Or is it just a specialized twin turbo set up?

Post by **themadscientist** » Thu Feb 20, 2003 9:04 pm

there is a swing valve in the manifold that controls the routing of the exhuast to the turbos.

Post by **Onizuka** » Thu Feb 20, 2003 9:04 pm

wouldnt that cause massive turbo lag for the second, larger turbo? I mean if i wasnt getting exaust gas before that means it has to start from a standstill.

it also sounds like a piping nightmare...

Post by **themadscientist** » Thu Feb 20, 2003 9:04 pm

It doesn't snap open it feathers the second turbo in so no lag is felt. They are ok but most cars with this type of system;RX7 and Supra do better when it is yanked in favor of a big single at the price of a little lag.

Post by **lessthanjakejohn** » Thu Feb 20, 2003 9:04 pm

Do RX7s have dualstage turbos? or is it one turbo then two turbos

Post by **themadscientist** » Thu Feb 20, 2003 9:04 pm

the 7 has a larger second turbo I beleive in a sequential arangement like the Supra.

Post by **dreamsOfSkylines** » Thu Feb 20, 2003 9:04 pm

I think the BOV vents into the second turbo to spool it up. The 959 pulled the arrangement off nicely. I guess aftermarket it would be pretty hard though.

Post by **themadscientist** » Thu Feb 20, 2003 9:04 pm

dreamsOfSkylines wrote:I think the BOV vents into the second turbo to spool it up.

No, if that happened you would fill your motor up with gasoline and maybe blow the muffler off the car. Can you imagine what would happen if you vented all that nice oxygen rich air into the exhuast stream. Your O2 sensor would think you just went wildly lean and hammer open the injectors and the unburned fuel already in the exhuast might explode in the now combustion freindly environment in your exhuast tract, yikes! :firedevil

Post by **big jon's 240** » Thu Feb 20, 2003 9:04 pm

themadscientist wrote:No, if that happened you would fill your motor up with gasoline and maybe blow the muffler off the car. Can you imagine what would happen if you vented all that nice oxygen rich air into the exhuast stream. Your O2 sensor would think you just went wildly lean and hammer open the injectors and the unburned fuel already in the exhuast might explode in the now combustion freindly environment in your exhuast tract, yikes! :firedevil

That would actually be kinda neat to see! Unless it was your car.

Post by **themadscientist** » Thu Feb 20, 2003 9:04 pm

actually I'm a goof, if someone got it on tape so I could laugh too I probably wouldn't care. Just send it into real TV and use the coin to buy a new muffler and a clue.:pface

Post by **dreamsOfSkylines** » Thu Feb 20, 2003 9:04 pm

i mean wastegate, i confuse the two sometimes.

Post by **C-Kwik** » Thu Feb 20, 2003 9:04 pm

themadscientist wrote:No, if that happened you would fill your motor up with gasoline and maybe blow the muffler off the car. Can you imagine what would happen if you vented all that nice oxygen rich air into the exhuast stream. Your O2 sensor would think you just went wildly lean and hammer open the injectors and the unburned fuel already in the exhuast might explode in the now combustion freindly environment in your exhuast tract, yikes! :firedevil

Actually, someone did his in an Eclipse. It kept the turbo spooled up quite a bit. Probably wore the turbo out quite fast. It was in a race car many years ago.

Post by **C-Kwik** » Thu Feb 20, 2003 9:04 pm

As far as the sequential set-up, it runs one turbo at lower loads/RPM, then spools the second one in parallel as RPM and load increases. The Supra uses the same turbo for both but since the exhaust flow and airflow requirements are split up between two turbos, it acts more like one big one after both are spooled. I believe the RX-7 uses a similar set-up from diagrams I've seen, but not sure if the same sized turbos are used or not. Either will work as my buddy had modified onlt the second turbo in his Supra and when it switched over, the car became a monster. It was more like what first turbo?

Post by **Red Lightning** » Thu Feb 20, 2003 9:04 pm

What's the advantage of running a sequential setup over two parallel turbos? It seems like a parallel tt is easier than the squential.

Post by **lessthanjakejohn** » Thu Feb 20, 2003 9:04 pm

A sequential means less lag. It is also more expensive

A parralel is used when your car has to much flow for one turbo or the placement of the cylinders (V) means that using two turbos would be easier and more efficient. Normally one turbo is more efficient than two.

Post by **themadscientist** » Thu Feb 20, 2003 9:04 pm

if done properly a sequential setup would get you going from a stop strong and bring on the second turbo just as the first one tapers off in a nice linear fashion. It would require a lot of skill, knowledge and experience to design such a system.

Post by **WDRacing** » Thu Feb 20, 2003 9:04 pm

Nothing better then N20 for turbo lag I always say. I will always go with a larger single unit over 2 smaller ones.

WD

Post by **C-Kwik** » Thu Feb 20, 2003 9:04 pm

lessthanjakejohn wrote:Normally one turbo is more efficient than two.

I disagree with this in the fact that this is not entirely true. It will depend on the turbos that are used, the flow and the boost level. One poorly matched turbo will not be as good as two well matched turbos. Secondly, even if the efficiencies were the same all across, there is some possible benefit to be had with the fact that using two turbos may place the turbos closer to their respective exhaust gas sources. And lastly, there could be some benefit from the lower momentum of having two smaller wheels then one larger one. I doubt so many extremely high HP Supras would agreewith you either. All of the highest HP versions out there seem to be running some kind of parallel TT arrangement. I would say that for most out there, slap on a good single turbo and it will probably put a nice smile on your face.

As far as sequential set-ups, probably a waste of money and time for the average person. Hell, I wonder how much cheaper it would have been to design the Supra with a somewhat larger single turbo then the messy, complicated, HEAVY, sequential set-up. Not to mention, it would probably be faster out of the box. Hell, if I cared about a broad torque band, I would just get the NA version.

Post by **lessthanjakejohn** » Thu Feb 20, 2003 9:04 pm

Well C-Kwik notice I said normally. And IN high horsepower, lots of boost, you Are goi ng to have lots of flow aren't you? Also, with two turbos =more pipes = more heat loss = slower spool up. Also at some point in high hp you are also going to run out of turbos to use, so you have to use two. ALso a big turbo might not fight in the engine bay too well....

Hell, if I cared about a broad torque band, I would just get the NA version.

Why would that be? your only going to be low on torque from below 3500 rpm. and the torque will only be able 10-30 percent lower than the NA version. Do you know anyone who races at below 3500 or 4000. Again that is normally...I have to do homework now and that was kind of a quick dirty answer but oh well...

Post by **WDRacing** » Thu Feb 20, 2003 9:04 pm

Most Supra's I've seen are running singles. Even Titan Motorsports is running a single.

Post by **machinehead** » Thu Feb 20, 2003 9:04 pm

only place where the sequential is more fun is on the street.

Post by **C-Kwik** » Thu Feb 20, 2003 9:04 pm

John, what is normal to you is not normal to everyone else. Which is exactly why I disagreed with the statement.

And as far as flow or lots of boost, who said I was talking about high HP? Flow affects the compressor's efficiency. Just take a look at a compressor map. Pick a flow rate and draw a line down that axis. Notice it changes with the amount of boost. Now pick a boost level and do the same. Notice efficiency changes with flow rate. That's what I was referring to. Not high flow. I was strictly referring to the fact that effeiciency changes with these factors.

Twin parallel set-ups on a I-6 can yield shorther runners than a single set-up. Lets assume an equal length mani. The length of the runners would need to minimally be as long as the distance betwwen the farthest port to the turbo. If the turbo's turbine sat equidistant from the #1 and #6 port, then it would be the at least length of the runner that goes from the #1 or #6 ports to the turbine. Now say you do go with a twin parallel set-up. Place the rubines equidistant from the #1 and 3 ports for one turbo and the #4 and #6 for the other. The minimum length of the runner would be the distance from the outer runner for each set of ports to the turbine. Now actual design may vary and of course fitment itself will also be dependent on the turbos fitting. But the point I made has to do with this concept. Since the twin set-up could have shorter runners overall there would be less loss of heat.

As far as fitting a large turbo, if you can fit two small turbos, in most cases you will be able to fit one rather large turbo in it's place.

As far as the NA comment, I was referring to having a broad torque band. I never said that is what I prefer. I just said if I CARED for one. And why would I only be low on torque up to 3500 RPM. This could vary with turbo size. And who said it was for racing? You make assumptions that you are not stating and are not obvious. I never disagreed with you entirely. Consider it a clarification.

Post by **lessthanjakejohn** » Thu Feb 20, 2003 9:04 pm

Post by **I am Technoman** » Thu Feb 20, 2003 9:04 pm

I herd a turbo pop the other night. It sounded wired I even herd the shaft snap. Me and a friend were driving at night down I-4 me in my Nissan and my fiend was in his 95 civic I know, I know but anyways this old 88 turbo MX-6 in front of me tried to pull on my friend and they start racing. I stay right behind the Mx-6 and a flame came out the muffler and I hear this “ping” Then their were flashers and the Mazda was dead.

End of story

dual stage turbos

dual stage turbos

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