Not sure this would be a good idea. Based on my experience the OEM ECU overfueled when I ran a boost controller and a 3" decat downpipe. This produced loads of black smoke when everything was spooled up on the rolling road. The danger is you can get bore wash running this rich i.e. unburnt fuel dilutes or even removes the lubricating oil from the bores and rings resulting in severe wear and consequent loss of compression. On track (Donington) I experienced some bangs when accelerating out of the final chicane (Goddards?) onto the pit straight. Sounded a bit like fuel igniting in the exhaust. I was worried it would damage the exhaust. Not sure if there were flames but my supercharged Elise flamed at the same spot according to onlookers and following drivers. Fortunately no bangs or explosions that I recall.
When I had later fitted a MoTeC M4 ECU it was set up with no over-run (i.e. off-throttle) fuel cut and ran fine. Later I activated over-run fuel cut in an effort to get better fuel economy. Shortly after this, during a track day, my engine detonated, destroying the ring lands and necessitating a complete rebuild. Although my water injection had also failed I suspect that the combustion chamber temperatures were higher than before due partly to the absence of cooling from the fuel being injected on the over-run. From observing most race cars they don't seem to use fuel cut. Having witnessed the Aussie V8 Supercars when I was at the Australian Grand Prix and Barbagallo in Perth they make a lot of banging noises when they change gear and spit flames.
On my track toy engine I am not planning to enable over-run fuel cut.
Hope that helps you decide what to do!
