Originally posted by wac
I'm pretty sure the ECU doesn't cut fuel in "mid-fire". Most ECU's use microcontrollers with PWM control registers to set and operate injector duty cycles. It would be pretty stupid for FHI to override the PWM auto-reload registers or gate the transistor output drivers to allow partial lean conditions that can lead to engine failure (and drive up warranty costs), when there are zero-cost ways of doing fuel cut at the rev limit by designing the firmware correctly.
I'd be surprised by a standalone use only ignition cut for a rev limiter. At those high rpms, the last thing you need is fuel (probably at max duty cycle) washing oil off your cylinder walls. I'd stay away from those standalones if I were you. Perhaps you're thinking about the MSD ignition-only products, where they have no control over the fueling?
Well, you're dead wrong.