[TheSnail]

Originally Posted by 90RS13

You are talking about compound turbocharging. Many tractors and heavy machinery use it, as well as some semi's. The second turbo doesn't "act as a restrictive heater", the set up does generate more heat in the charge air, than a single or sequential system, but with a large intercooler it's usually not a problem. As far as spooling goes it's great. You use very small turbo's, so they spool very quickly. Just think, a 1.4 pressure ratio can be easily achieved with a very small turbo. Ok now look, in a single turbo system, when your turbo is at a pressure ratio of 1.4, you would get get 5.8 psi of boost pressure. [atmosphere at sea level)*(pressure ratio)-(atmosphere)=(boost pressure.]Not enough for most enthusiast. But when in series, with 2 turbo's at a 1.4 pressure ratio, you will have 14.1 psi, of boost pressure. So with the spool time you would get from a turbo optimized for 6 psi, you can have 14.1. For perspective, a turbo at a pressure ratio of 2, you would get 14.7 psi. If you know turbo's, the difference between 1.4 and 2 is more than it sounds. Now there has to be a catch right? There are many. It's alot harder to have the room for a compound turbo system. It also does generate more heat, so you need a bigger intercooler and seperate oil, and/or water feed lines for each turbo. It can also be hard to find small enough turbo's to use for daily drivers. Also, when you start flowing alot of air, the small tubines create a lot more back pressure. It has beed done, even on performance cars though, and with success. Hope that makes sense. Tell me if I forgot anything.

Good stuff, I wish we had more Germans on Zilvia.