I have had some older sets of twins but what i noticed was they come on sooner and pull evenly but compared to the hit of a single, they did not hit as hard as my 2.8. They were easier to light in spur of the moment hits but was not the "awesome you gottta get twins" that i was told.
The reason they technically should spool faster is because the atmosphere turbo is doubling the pressure on the top turbo. We breath in 15 lbs or something like that so the big charger is putting 30 lbs to the high pressure turbo so it has to work less to move more air. But now you got twice the air and like most people have twice the fuel all still going through the same little exh housings and turbin wheels which to me is overloading them (too much drive pressure) which causes heat, blown hg and poor performance. I do not think internal wg's are enough to compensate for 80- 100 lbs of boost going through stock or slighty bigger turbos. To do it correctly and get fast spoolup, you need like a ED wastegate and bypass the exh past the atmosphere charger so to not overspeed it.
Long story short, my experiance is it is a pain in the butt for the maybe little bit of improvement twins provide unless you want to spend money on custom sets like MPI's or others that do this research for you. Simply hanging a s400 under the stocker is pointless in my opinion. GIVE ME A SINGLE ANYDAY.
Tim
