[Walt Fricke]

Well, the 80-83 3.0s used fuel pump cutoff as the rev limit. No problems there, and it sure is quick - pressure drops below injector open pressure pretty much instantly. Just as fast as ignition cutoffs of various sorts.

I don't know as much about 3.6 EFI, but I am dubious that there is any significant overrun. However, where ignition is powered directly from the ignition switch, I'd put a relay into that circuit if I wanted to use that as a cut-off. Way too much current flow to want to run through that little switch.

Here is something else to consider. Our cars have a nice cut-off switch - the key. The only use for these battery/engine cutoffs is racing, so corner workers can shut off the battery so sparks don't create trouble after a crash., fuel pumps can't keep running, and so on. And, incidentally, to turn off the engine should it happen still to be running.

I don't think hard starting is going to be a practical issue. For most of us, this switch is used on a running engine on those rare occasions where race officials are checking safety equipment.

Carbs are a different matter when it comes to cutting the fuel pump off - they will run on, so that's not an option - the engine has to stop promptly.