Quote Originally Posted by chinacrisis View Post
1. is it correct to say that a well-tuned venturi/emulator conversion will be able to maintain the FC and power of the car at low rpms (up to 4k)?
No. Venturi systems can get close but not equal the FC of gasoline. Expect a loss of fuel mileage of 5% to 10% depending on tuning. Running lean, it is possible to match or exceed the gasoline FC figures but performance suffers as possibility of engine damage in the long term.

2. is it correct to say that the FC and power loss inevitable with a venturi/emulator conversion will be found only at higher rpms (5k and above?) ?
Yes. Also air filter condition can affect FC figures as well.

3. is it correct to say that the advantage of a closed loop system versus the open loop system is that the settings for tuning it will be provided by the ECU, but on-the-fly performance will be the same as a well-tuned open loop system?
SGI systems still have an advantage of potentially better air-fuel mixtures at ALL rpm range. Even a well tuned venturi system has one major drawback, the venturi itself. This constricts the air-flow which increases the intake manifold vacuum pressure at higher RPMs. SGI systems don't restrict the air flow, hence better high RPM performance.