Flat shifting isn't new, but after my recent install, I have noticed a number of advantages, which apply to supercharged applications. So, if you're using an aftermarket computer which supports flat shifting (such as megasquirt), then IMO its worthwhile wiring it in....
Flat shifting is where you have a clutch switch tied into your megasquirt, which tells it when your shifting. You set an activation rpm, and an minimum rpm to hold the engine at, while your shifting, that is, if you shift really slowly.... As your shifting, you hold the throttle a WOT and the MS cuts fuel until your engine slows to the holding rpm.
The miata has 2 clutch switches, one of which tells the stock computer when you have the clutch in, which is perfectly suited for this application.
Here are the reasons why:
1. Boost gets back to maximum, right away after a shift.
Sure, the boost returns pretty quickly with a supercharger, but it's not immediate. The bypass valve needs to close, and then the SC needs to fill the intercooler (if equipped) and intake manifold. For my car (which has a large intercooler and bigger than stock manifold), I calculate .18 seconds to reach full boost, after reapplying the throttle.
2. You can shift quicker.
-first off, you don't need to think about co-ordinating a throttle lift, so you can focus more on the other parts.
-second, since the supercharger is working hard, generating boost, your engine will decelerate quicker. In my application, the engine slows down nearly twice as fast, with the supercharger pumping. This matches the engine rpm to the next shift rpm you want quicker, making the synchros work less and the shift itself easier.
Here is a screen shot of a shift event, captured on a MS2. (click on image bar to see it full size)
White=RPM Red=boost Green=fuel.
The time from fuel cut to restore = .2seconds (yes, according to MS2, but regardless, datalogs reported a reduction in average shift time)
For more information, do a search on flat shifting (links dating back to 2008!)
I adjusted my switch, so it would active just before the clutch disengages.