Researching the addition of a ZEX nitrous system to my 2013 GT 5.0. Came upon a long discussion somewhere on the issue of rpm limiters and nitrous sytems. I searched here and found little so, some correct info for the curious. My 2013 PC/ED manual say on the 2013 Mustang and most all other 2013 Ford products, rpm limiters work by disabling some or all of the fuel injectors. With the ZEX system which adds raw fuel into the CAI after the mass air flow but ahead of the throttle plate, this means a lean mixture condition since the fuel injectors are not functioning to keep the thing roughly stoichiometric while the rpms are above limit. It also seems to me, that with spark still present that lean engine will keep on truckin until something bad happens unless the driver gets out of the thing quickly. With your mind on racing, getting off the throttle quickly may not be at the top of the memory stack. Moral of story is this with a ZEX system; an rpm window switch would seem to be a really good idea for the nitrous/fuel arrangment they use in 2013 Mustang applications. Hope this is useful info.