[TitaniumTT]

Spew all the thoughts that you want in here, that's the purpose of the thread.

Diesel AIT's vs Rotary AIT's - not all that critical in diesel applications as diesels compress the air to superheated status THEN inject the fuel causing combustion. Typical diesel comp ratio's are 20+:1 and boost is in the 40+ range....... yeah. We all know what a poor intercooler can do for a rotary.

As for the function of them..... This is what I'm wondering as well. My friend was thinking about going twin charged - and infact there are some Yanmar diesels (I'm a marine guy too) that use twin charging. The way the Yanmar system is setup to work is with a supercharger and a BIG turbocharger. The supercharger gives the instant response and is run off a clutch system. When the ECU detects mani pressure above what the supercharger can produce, the supercharger is shut down and the turbo does the rest. Interesting.

What I'm gathering from these compound turbo's is the smaller gives the instant reponse while the larger is spooling up. This of course hurts backpressure which is a major hindrance for a rotary. But how much? Dunno until it's tested. For YEARS internet myths surrounded the twins saying they were a backpressure nightmare. In reality they are no worse than MOST other turbo's. I stay with in the generally accepted 2:1 ratio but I believe I am right at the limit of the effeincy of the stock hitachis. I would love to see what the BNR's could do BUT it's not all that much of a challenge.

After my ramblings....... the compound system, it seems like the smaller provides the instant repsonse that I'm looking for while the larger is gaining momentum. But when the larger somes online is the positive pressure from the larger being further compressed by the smaller turbo? I would say..... yes, yes it is. So then air temps as Phil pointed out can come into play. Such to the point that a LARGE Air-to-Water intercooler are needed. OK, not a problem.

Maybe the thing to do is not plumb the outlets of the turbo's in series, but instead use some sort of boost activated exhaust cut-out instead? Size the turbo's such that as one is out of breath, the other is ramping up. But then will that throw the smaller into surge? Is that why they are plumbed the way they are in the first photo?