Originally Posted by search

Why would I want to convert my sequential twin turbo over to a non-sequential twin turbo?
If your car is bone stock you probably do not want to convert it.
If you have replaced your pre-cat with a downpipe and your main cat with a mid pipe, the pre-spool timing of the stock system will be off due to faster turbo spool up.
If you are running an aftermarket boost controller it will most likely not be designed to also control the turbo pre-control gate which can and will quickly cause excessive wear to your transmission and drivetrain.
Add an aftermarket intake and a larger intercooler and the prespool timing problems will increase.
With the above mods you will need to enlarge your wastegate anyway which is trivial to do while the turbos are apart for the NS conversion.
Some say there will be excessive turbo lag with a NS system...Is this true?
If the exhaust is otherwise bone stock, then yes there will be considerable turbo lag.
If the main cat is in place and the pre-cat is replaced with a downpipe, and the engine is *mildly* street ported, stock IC (or upgraded IC) and upgraded intake, stock cat back (or upgraded), the lag will not be a major concern except for the hard core Auto-X racer (who should have a fully open exhaust at this point anyway)
With a fully open exhaust it is not a concern.
With a fully open exhaust and an upgraded intake and IC it is even less of a concern than above.
What are the major benefits besides correcting the pre-spool timing problems with an open exhaust
There will be considerably less vacuum lines to worry about, and you will no longer need the 2 black vacuum and pressure tanks which will provide larger paths for air to flow around the engine cooling it more and helping to prevent the baking of underhood vacuum lines and components.
A smooth consistant, predictable boost curve that will come on strong and stay there through redline unlike the stock 10-8-10 PSI mess. This smooth boost curve means you no longer have to worry about the transition point occuring during a corner (which could and sometimes does send the car into a tailspin)
Less restrictive exhaust path, which ultimately results in less backpressure being seen by the engine (IE more power, and less internal heat)
It will become trivial instead of impossible to troubleshoot problems with the turbo system (if you have any :)
What are the drawbacks?
The dealer service department will not know how to work on the car with all the vacuum lines ripped out...wait they can't normally work on the stock system anyway :)
You will have to work on the car yourself due to the above reason...wait thats good because of the above reason.
Will knock you out of the showroom stock class (not a big concern if you are racing only for fun and not trying to go for nationals)
Excessive, but livable turbo lag when you are driving the car that one day a year with the stock exhaust system on it :)?