Okay, I read some of this thread (but not all... I'm sick with the herp... I mean, cold--I got through page 2 or so). Brian, I think what you're goal is--this is an okay way to go, but there's a better way and you can easily make the uber flat torque curve, but you're not going to like what I have to say.

You should make your own sequential turbo manifold/system. If you do a compound turbo you're going to run into a few problems, especially when you want to get a specific torque curve. Since you're flowing the exhaust flow into a small turbo, then into a large turbo (st, lt, etc), you're actually removing a certain amount of energy from the exhaust flow in the st which will cause the lt to be under spooled. If you can by-pass the small turbo such that it's on pep the entire time the large turbo has matched the pressure output of the lt you will have a much flater torque curve than a compound.

The way I imagine the sequential manifold set up is by two wastegates. When the pressure of the small one hits the target value, the waste gate activates and dumps the wasted gas into the lt. lt reaches peak pressure and will be more efficient in it. For instance (and just as an example), here are some compressor maps from turboneticsinc.

http://www.turboneticsinc.com/sites/...files/60-1.gif
http://74.208.101.201/pageimages/tec...sor_map_01.jpg

As you can see from these two turbos the 60-1 will run out of steam just as the HP76 is kicking in. You then get more mass flow of air compared to the 60-1 and no bad will come of this. Since the 60-1 is just getting enough exhaust to stay on pep it will always be ready for action when you let up the throttle and the large turbo drops back out of its efficiency range, and you wouldn't have the energy losses from compounding the exhaust stream.

Put it another way: There are three different scenarios that the above performs.

1) The small turbo spools quickly providing the torque you want early on the large turbo dumps its slightly less compressed air into the intake stream of the small turbo to help the large turbo spool quicker.
2) The large turbo spools to the same pressure as the small turbo and you run with an increased mass flow of air
3) The large turbo exceeds the small turbo pressure and as a result the small turbo dumps its charge into the intake stream of the large turbo which is better at the higher rpm.

This and both turbos receive the full benefit of the temperature difference from the exhaust.

In fact, I have an idea about how to do both the intake and exhaust manifold.... I believe this very well is the only way to get the torque curve you want without the downsides of the compound turbo set up. There is another way you may want to look into:

Basically instead of pressurized air being pushed back into the intake, the turbo directly puts the energy on the e-shaft (through a series of gears to increase torque).

I found a pic to what I'm talking about:
http://www.heat2power.net/images/com...bocompound.jpg
http://www.heat2power.net/en__benchmark.php

The good stuff was in pages 3 and 4. ;)

I'm not sure I really followed what you said vex... The 60-1 is a pretty decent size turbo to be using for fast spool, it works well as a medium size turbo and is a good compromise between power and lag for a single turbo setup. Not ideal for instant response, but that really makes no difference for the theory....

If you're saying have a small turbo basically setup like normal, and then a big turbo that's run off of the wastegate exhaust of the smaller turbo... I don't think that would work well. The amount of exhaust energy coming out of the wastegate pales in comparison to that coming out of the turbine outlet. The large turbo would have very little exhaust pulses to get it moving, and would probably contribute very little extra air to the engine.

Next, the large turbo would be a restriction to the wastegate which would almost certainly cause an over-boosting situation for the small turbo.

The other system you mentioned, which seems to be separate from your first idea, is generally called a turbo-compound system. Where a series of gearing is attached to the compressor instead of a compressor wheel. This system adds so much complexity, and would only work well in a diesel application where massive amounts of exhaust gas and pressure is created.

Compound turbocharging (like we have been discussing), where one turbo flows into the other would make a very flat torque curve with properly sized turbos. With a small primary turbo you could have full boost before 2000 rpms and with a properly matched larger turbo maybe a gt42r you could make well over 700 hp if desired. I think you will lose a little engine efficiency from the added exhaust restriction, but the additional power made by the setup will vastly exceed anything lost. I would be concerned with backpressure creating too much heat and excessive EGT's. Only testing would show if this is an issue.

Another idea is to use a roots style supercharger for instant boost, and make it a compound setup using a larger turbo. This would actually remove restrictions in the exhaust since you can use a larger A/R housing, and the supercharger will give you instant response and boost. I personally think this is the simplest and most logical solution to having your cake and eating it.

Sorry, I'm on cold meds and my thought process will be fuzzy for a few days until I'm over this. I just used the 60-1 and the other Turbo as examples of their respective comp maps.
No, not set up like that. You have both turbos plumbed such that the first turbo (60-1 in the example) received a majority of the exhaust stream to ensure quick boost build and response. The remaining exhaust would be routed in through the large turbo so the exhaust flow would still be causing the larger turbo to spool. As soon as the smaller turbo starts to eek out past its efficiency range or the desired pressure is reached, the exhaust is then diverted via an external wastegate to the large turbo stream. The temperature difference should be negligible to allow the large turbo to spool to the desired pressure.
That really depends on the wastegate and how the pressure in the exhaust system will behave. With nominal exhaust temperatures the large turbine should not be the restriction in the exhaust flow, but rather the small turbo will be and as such the diverted exhaust gases from the manifold, and from the wastegate will feed to the large turbine, causing the large turbo to increase energy conversion.
It's actually been used fairly effectively in aircraft applications as well. Though the gearing I don't think would be that complex. A simple unit similar to a transmission should allow for easy application to a car. From the picture I posted it is actually from a Volvo engine.
I think it will be a vary large issue and would need to be evaluated prior to doing any testing. I think it's all in the sizing as you and others have said, though I see it becoming a much larger problem as there is no by-pass for the exhaust. Looking at my friends tuned sequential FD the torque curve was ridiculously flat, and I honestly think that's where the best performance is going to come from; something similar, but with a much more scrutinized design.
This idea has merit, and I agree.

Oh I didn't know you were suggesting the turbine outlet of the SmallT would be dumping into the the LargeT. That would work fine then, the velocity would still be high enough to spool the LargeT. You do realize the compound turbos have wastgates too right? They are plumbed in the same manor you're talking about. Sounds like there is really no difference in operation for the exhaust side of what you're suggesting. And in both cases you still run into the problem of two exhaust housings/wheels in the stream of the exhaust which will increase back pressure/EGT, especially if the first is a small housing to help spool.

The only difference I see now, is the cold side. In a compound turbo the LargeT cold side feeds into the inlet (where the air filter goes) of the SmallT. This is where the compounding takes place. The boost is "compounded" or multiplied. While in a sequential system, there is usually a butterfly valve to keep the turbo that's "working", flowing only into the manifold, then the butterfly opens and allows the second turbo to contribute to the total volume of air, but it in itself would not increase boost pressure. The difference is much like the following diagram of 2 pumps in series vs parallel. Series would be compounding, and parallel would be sequential.

http://i10.photobucket.com/albums/a1...emaaan/pvs.jpg


Here you can see the wastegate in the image below of a compound turbo.
http://www.atsdiesel.com/ats_new/ima...2272202942.gif

I'm sure you know this already, but exhaust gas velocity plays almost no part in turbine spooling. It's temperature and pressure differentials that play the biggest role in it. What I was suggesting was that the small turbo not take up 100% of the exhaust gas flow from the manifold, but that the manifold feeds both the small and the large--which is different than all the compound turbo setups I've been shown thus far. The manifold would need a "wastegate" or a gas diverter to ensure that the large turbo would not "steal" all the temperature/pressure of the exhaust, but have just enough to spool when the small is reaching its efficiency limit.
I'm aware, but the exhaust flow in the compound setup is different from what I'm suggesting. Couple it with the fact that a small turbo has a very limited efficiency range you really become limited in the turbos one will be able to run. Couple this with a rather large increase in AIT and I see a bad time coming. Even if you held the AIT's low by some super intercooler process the pressure levels one would tune for would not be worth headache the system offers.

EDIT: Just saw your direct comparisons, care to elaborate on those plots?

I have two routes that I'm going to be taking with the FD. If one doesn't work because of mechanical/temperature limitations, I'm still going to try this out. The way that I see it working best is basically 3 wastegates. The Smaller Turbo being internally gated as well as a rather large WG right at the merge coupler. The Larger Turbo being internally gated, but with a LARGE internal gate. The exhaust shall merge at a collector prior to the ST. The ST being internally gated to control boost to a preset level. Once the ST's internal gate is 100% duty cycle, the gate on the collector will begin to open to control boost yet again. This will happen rather low in the RPM range, I'd shoot for ~3k. After the other gate begins to open and the LT is spooling, it becomes a juggling act as to when the LT becomes "active" I think y-valve or a exhuast cut-out would need to be used. This is more of a sequential system though.

So, Exhaust flows from the block to the ST. From there, the DP if you will of the ST feeds the turbine of the LT. The external gate will alse feed the LT. The LT is internally gated and has ultimate control over the boost so it needs to be large.

I believe, after doing a bunch of research that the compound will generate too much boost. As a multiplier, I think it's might be a little much. Although, there's still a ton of research to do on the subject and it is something that I still believe has merrit. I think there are simpler ways to get the torque curve that I want. If anyone says V8 I will kill them :rofl:

A super intercooler system isn't something that is too hard to accomplish. My setup works retardedly well and the core is somewhat small.

Aux injection is something else that can be employed although I'd rather not. We'll see in a few months when I really start humping on the FD.

I spoke to a guy running a compound turbo setup on a eagle talon running 8.97 at 156 mph. He said he did it because the turbo he was running, a 1.32 T6 s475 wouldn't spool until 7000 rpms on his car, so he was using nitrous to help spool it. Then he added a t3 50 trim in a compound setup and it sees full boost around 4000 rpms.

This is what I found out from him, peak power is pretty much the same at the same boost levels. In his case he runs about 40 psi, which is medium boost for his engine. You do not have to run extremely high boost levels in a compound setup.

You choose the large turbo for whatever max power you want, and you choose the smaller turbo for whatever spool you want. Obviously they will have to be somewhat matched or you won't have the large turbo spooled before the little one runs out of breath.

His intake temps are the same, though he never measured pre-intercooler temps which would be more accurate. He said his drive pressure to manifold pressure is really good being 1:1, "Which is not going to happen on a single turbo that will actually spool on the car" (his words)

The advantage of the setup is much faster spool with a high top end, disadvantage is complexity and cost. He's running 2 wastegates on the first turbo to keep it from boost creeping, the second turbo also has a wastgate that he uses to adjust the boost level.

It sounds like a really good way to go, and the concern of needing to run high boost is not the case. The pressure ratios are divided between the 2 turbos. Almost like it's one turbo with a very broad map. Exhaust restriction and high AFR's are also not the case.

As I mentioned, they have higher boost than backpressure on compound setups for diesels! If I had the $$$ I would do it with the 13B!

That could mean 40lbs of boost and 39 psi though. EMAP on a rotary needs to be kept as low as possible. Anything over a bar and the EGT's get a little high, or so I've found.

I would like to know what Dudemann's EMAP is.

I would also like to know what the EMAP is of a bunch of other singles

The stock turbos would definitely have a high emap considering how restrictive the manifold is. It would be difficult to have a fast spooling turbo with a low emap, since restriction is what really helps get the turbo moving. One day I'll check mine. I have a feeling the manifold back pressure won't be too bad in the compound setup since so much gets diverted around the first turbo once it is spooled and the wastegates open. The only issue is it will require multiple gates or a very large gate to divert say 600 hp worth of exhaust.

The stock twins EMAP isn't nearly as high as everyone thinks. It's internet lore. I stay within a 2:1 ratio. I've posted the datalogs before, but they're not as bad as everyone thinks.

The thing with the rotaries is that .... and this is MY theory.... that the EMAP needs to be kept as low as possible for a variety of reasons. I think with large enough gates and proper turbo's it can be done.

I would love to know what some of these mani's are making in terms of EMAP. The problem with the stock mani is the internal maze. Make something tubular and I bet it would go way down. Then you're outflowing the turbo's though (Roen) so the stock hitachi's won't work.

Meh, it all depends what the manufacturer says when I call them in a few months. I'm getting the itch to work on the FD. I'm getting the itch to work on the FD when I have two FC's to completely assemble and one to paint in the next 5 weeks from yesterday :banghead:

lol, I got called out without even being present in this thread.

It's a tough mission finding something to provide greater power than 450 whp while maintaining Mazda's sequential system.

Fix your damn sig, Brian!