[dudemaaan]

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.