I can make my Cosworth spit flames at overrun if I want
All I do is turn off overrun cut off, igniton table at about 0 at overrun, and AFR table at about 10 at overrun. After 1 or 2 pulls with full boost it spits flames at overrun
I do the same thing on a mates car to keep the turbo spinning during braking before corners.
-Ford Sierra Cosworth 4x4, project car with MS3X, IAW Weber mode and sequential fuel. T3/T4 hybrid ballbearing turbo. RS500 type IC and radiator, and about 1 bar more boost more than OEM, controlled by MS.
-84 Ford Sierra 2,0ohc GL, soon to be MS'd, NA tuned with rallyecam and TBI.