is there any way to make a "quick spool valve" for a non twin scroll turbo... in my head i'm thinking, if i used a butterfly half the diameter of the turbine housing entrance. so really half a half circle. it would have the same effect but i've had people tell me it wouldn't work and frankly i don't wanna hafta build it to find out.
my turbo is off a grand national and the inlet is a circle

or is it the split housing of a twin scroll that makes all the diference?

 

your idea will only cause slower spool. The reason a quick spool valve works is a twin scroll turbo has separate scrolls.. you end up forcing all the flow through one scroll instead of both when the valve is closed. IE you artificially created more back pressure for the motor, and temporarily created a condition where your turbine housing A/R is about half of what it is with both scrolls. This tends to help more for larger motors than smaller 4 cyl motors.

Now without two scrolls, all you would be doing is adding restriction that the exhaust flow would have to travel around before filling up the whole housing. It would work about as good as putting a block of plate on half of each exhaust port.