I just had an idea, and was wondering what you guys thought of this. The idea is a Twin Turbine Turbo. Its just as it states, a turbo with two seperate turbines that are connected by a shaft. The first turbo would be relatively small and spool up very quickly, it would have a shaft connected to the second turbo sitting next to it. That shaft will have a centrifigual clutch on it. So once the smaller turbo spools fully the second turbo starts to spool. Thus allowing twice the boost with none of the lag. what do you guys think of this idea?

The problem with that is the heavy rotating assembly - two turbines, a clutch, etc. Spool would probably be pretty slow even with a small turbine. A better solution is a sequential twin-turbo setup, where there is a valve that diverts the exhaust to one turbine or the other, like the stock turbo setup on a Supra. This system works well, but its rather complex. Also, the cam is only going to be very effective through a few thousand rpm, so having a wide boost range isn't all that beneficial. 3500rpm of powerband is plenty, after that you shift anyways. It would make the car more driveable, but as for accelleration, there is little to no difference.

Try a VNT turbo, similar idea but more effcient.

If any turbo idea pops up in my head it would be a twin exhaust turbine solid shaft double sided compressor arrangment.....

Turbine-------Compressor--------Turbine

with the compressor you have 2 inlets 1 outlet , and with 2 turbines you can put more exhause energy into spinning up the compressor

With a V engine you could position each turbing to connect with each bank from the exhaust headers.

you could place it in front of or in back of the engine depending on space... and plumbing issues wouldn't be as bad. if up front you might be able to run a stright pipe from the outlet right into the intercooler.

with this you wouldn't have the weight of another compressor so it would be about 3/4 the weight.

the larger spaces between the turbines and compressor would allow more room for water cooling jackets and bearing oiling, but overall put space between the compressor and hot turbines. but i guess that would kill the weight advantage.

who knows i can't think of any more benefits of this arrangment over seperate turbo charging units. i guess you could really call it a Bi-Turbo or a one-half-turbo.

I'll leave the rest of you to criticize my thoughts. :smile:

Divided inlet is the only thing I can think of.

Other than that, go with a parallel setup or a sequential.

Personally I would prefer one large turbo with the lag than two small ones. But thats just preference. To each thier own.

Your idea for twin turbines on one compressor is interesting, but it wouldn't be of much(if any) benefit over 2 separate turbos. If you've ever taken a turbo apart, you know that the turbine wheel and shaft make up the vast majority of the rotating assembly in a turbo - you've doubled both of those, and saved the weight of one compressor wheel. So instead of having two turbines, two shafts, and two small compressor wheels, you have two turbines, two shafts, and one large compressor wheel(or two small ones, same difference). If you have two inlets and one outlet, that would mean two compressors, right? So you've just joined two turbos at the compressor. In reality, you've just complicated a twin setup.. How would you route the compressor inlet if there would be a center section(i guess it would be half sections now?) on either side of the compressor wheel(s)? A clever setup using a banjo type inlet might work, but why? You've also taken another of the big advantages of a twin setup away from the V/HO engine - seperate exhaust systems to prevent cracking with thermal expansion. You've also made it less flexible in placing it, and larger than a single 'big' turbo. Interesting idea, but not much merit to make it worth producing.

yeah it was just an idea. . .i wasnt planning on doing or anything, just something for discussion.

i think a two sided compressor would be a great idea as they use them in some turbojets (usually APUs). the only difficulty i could think of would be pulling the intake air (for the compressor closest to the turbine) around the axle.

has this been done? if not, why?

Since the turbocharger is using a single axle the compressor and turbine must be designed for the same speeds so one can't just mix small compressors with large turbines. In gas turbines two compressors are usually used for stages, to increase the pressure more than one stage can. Some turbines also use separate shafts for compressor and turbine with gearing in between.

Turbochargers use very high speeds, the typical automotive turbocharger use 100,000-250,000 rpm dependning on its size. At these speeds everything is very complicated and even small friction losses is a large issue. Shaft motion and stiffness of the bearing section is also very important.

In a turbocharger the turbine is the main reason for the inertia of the rotating assembly, for that reason any weight reductions should be concentrated to that part. Turbines can be made of titanium aluminide or ceramics to reduce inertia. A TiAl turbine has around 60-70% of the inertia of an inconel turbine.
Friction is mainly a concern for spool-up and low turbo speeds as the turbine power is then limited.

well a simple centrifugal (as apposed to axial) gas turbine uses one stage of turbine and only one stage of compression though the compressor is dual sided (same compression and flow from both sides). this is done because while it may weigh the same or slightly more than a larger single sided compressor, that weight is focused closer to the center of the compressor, allowing it to spool faster and more efficiently.

well a simple centrifugal (as apposed to axial) gas turbine uses one stage of turbine and only one stage of compression though the compressor is dual sided (same compression and flow from both sides). this is done because while it may weigh the same or slightly more than a larger single sided compressor, that weight is focused closer to the center of the compressor, allowing it to spool faster and more efficiently.
Yes, this is the reason why 2 turbos offer slightly less 'lag' than a single large compressor. However, it is more of the smaller turbine than the smaller compressor, as was already mentioned. The turbine is the vast majority of the weight. Two turbos vs one offer VERY slight spool advantage, and that is reducing turbine diameter - going from one large compressor to two smaller ones would offer an extremely small ammount of lag reduction, probably nothin noticeable.

The TRUE reason that twin turbo offer better spool-up is that the exhaust pulses are more separated, leading the a more pulsating pressure in the turbine inlet and thereby a higher turbine reaction. This method is also employed by the twin scroll turbochargers.

Most APU's and similar small gas turbines are using a single radial compressor, one axial turbine for powering the compressor and an axial power turbine. This is how the Garrett JFS100 and Plessey Dynamics Solent.
Larger turbine engines using centrifugal compressors are usually using a multistage axial flow compressor and a centrifugal compressor as the final stage, among these I can mention Rolls Royce Gems and Nimbus, GE T700 and the Allison helicopter engines. Some engines are using two stage centrifugal compressors like the LHTEC T800.
Double sided impellers are quite uncommon, there are also some discs that serve both compressor and turbine.

The inertia of a turbocharger compressor is insignificant compared to its turbine. Performance of both is dependant on blade tip speed.

ellaborate on the twin scroll. i was always curious about specific details of it. (and too lazy to find out)