I may be wrong but are you sure your not confusing twin entry with twin scroll ? What you have described to me here sounds like twin entry.
Twin scroll as I understand it -
The scroll area dictates lag, the larger it is the more it flows up top but the more laggy it is. At low rpm's there is less exhaust gasses flowing out the exhaust and hence is harder to spin the turbo, so a smaller port is used (only one of the exhaust ports are open), after a certain rev range or boost range, an actuator opens the second exhaust port to the turbo allowing more gases to enter and spin the turbo.
The idea of the twin scroll is to minimize turbo lag.
As I said, I may be wrong .....
Quote:
Originally posted by texan
the twin scroll is just a more advanced tubine housing design that helps to enhance exhaust gass energy utilization while minimizing ehxaust manifold backpressure and hence potential for reversion.
Think of your average inline 4 cylinder. Ever notice how in 4-2-1 headers they always pair cylinder 1 with 4 and cylinder 2 with 3 when merging the 4 pipes into the 2 secondaries? The basic firing order dictates that pairing these cylinders together will give the longest possible gap between exhaust pulses traveling through the pipes, thus enhancing flow while minimizing reversion. The twin scroll operates with the same basic principle in mind: keep the cylinders firing into an exhaust pipe that isn't already stuffed full of exhaust from an adjacent cylinder. With turbo cars this can be especially important as at higher RPM exhaust backpressure is usually significantly higher than atmospheric pressure, and often higher than intake manifold pressure as well.
So the twin scroll creates two exhaust paths instead of one, allowing for that increased separation in exhaust flow that is key to keeping everything from stacking up behind the turbo and causing reversion. It also helps to preserve the exhaust velocity of each pulse by offering a smaller overall volume to hold each one, so the turbine impeller is more easily spun up by a given total amount of flow than an equivalent single scroll design. Or at least that's the theory behind them. Answer your questions?
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