Twin scroll?
 

Ok so whats a twin scroll when referring to turbos because someone has a twin scroll turbo for sale very cheap so i was wondering? whats the advantage / disadvantage?

twin scroll was used on the s4 turbos

s5 turbo's did away with it by using equal runners and by not angle'n the manifold.

not an FD thing. They prolly meant something with the sequential turbos.

What are twin scroll or divided inlet turbine housings? What are the benefits of using a twin scroll turbo?
A "twin scroll" or "divided inlet" means that there are two separate volutes within the turbine housing. The main reason for doing this is to isolate the pulses coming from each exhaust port and maintain more of the pulse energy from each cylinder all the way down to the turbine wheel. There are no differences between the turbine wheels used in open or single inlet turbines compared to those used in twin or divided inlet turbines.
Generally speaking, a divided inlet turbine setup will respond faster and produce boost quicker than single or open design of the same nozzle area, of course this is dependent upon proper execution. The simple fact that a divided housing is used does not guarantee these results.

While it does not cause any problems or harm to run a divided inlet turbine housing on a manifold that is an "open" design, none of the benefits of the twin inlet will be seen.


info from http://www.forcedperformance.net/faq.aspx

mazda went a bit further

on the twin scroll on the FC's there is a flapper door to quicken spool.

Both the turbos are technically twin scroll by that def (divided) but only the s4's are refered to by twin scroll b/c the actuator. That's it what Mazda called the system they designed.