your running a chevy right they like to have wide open headers they run better with almost no back pressure.
fords make better power with back preasure.

i've been around the tracks and engine builders for years now and this is the first time i heard anything of this sort.
most of the time the reason u here drag cars rev at the line right before they stage is to clear the carbon out.because race gas in a car just idleing can foul a plug up fast if the tune is off some what and there tring to clean the plug of any debrie on the tip.