| Message | don't know how fast our ecu clock is or how many clock cycles it takes for our ecu to sample a piece of engine data (rpm), make a caculation with it, and excecute  what's neccesarry (add fuel, decrease fuel,cutoff fuel), but I would think it would have to be at least in the low ms range(probably µs range) since engine conditions usually changed pretty quick.  I don't think the ecu would have a problem detecting it, unless whatever sensor is used to detect rpm has a slower ramp-up time than our engine.  Than again it wouldn't makes sense to use a sensor that slow for a critical part. Ash of anyone would probably know this answer since he's an ecu guy. I think the stock tach is just not mechanically accurate enough at high rpms to be able to tell, I dunno... 
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