The effectiveness of equal length header tubes is widely debated.
Assuming that a header is otherwise properly designed (and many headers are not), equal length primary tubes offer some benefits that are not present with unequal length tubes. The benefits are smoother engine operation, tuning simplicity and increased low-to-mid range torque.
If the header tubes are not equal length (most commercial headers are not equal length), both inertial scavenging and wave scavenging will vary among engine cylinders, often dramatically. This, in turn, causes different tuning requirements for different cylinders. These variations affect air/fuel mixtures and timing requirements, and can make it very difficult to achieve optimal tuning. Equal length header tubes eliminate these exhaust-induced difficulties.
If a header is otherwise properly designed for it’s application, equal length header tubes are, of necessity, longer than unequal length tubes. The lengths of both primary and collector tubes strongly influence the location of the torque peak(s) within the powerband. In street and track performance engines, longer header tubes typically produce more low-to-mid range torque than shorter tubes and it is torque that moves a vehicle. This begs the question... Where in the powerband do you want to maximize torque?
In order to keep the torque curve the same for all cylinders, it is important that primary pipes be equal in length. Exactly how equal they have to be is more critical on uncorked race cars than for the vast majority of mild-engined street cars running through mufflers. In most applications, pipe length deviation of 2 to 3 inches on a set of full-length headers is not a problem.
As high pressure forces that gas toward an area of lower atmospheric pressure at the end of the headers, it creates an expanding vacuum in the primary pipes. At the collector, the gases suddenly hit an area of much larger volume, which causes them to slow down. At the same time, the vacuum draws a refracted wave back up the primary back toward the engine. Since all 3 pipes at one bank of the engine meet at the collector, a wave might move back up one or more of the other 2 primaries, which enhances the scavenging in the correlating cylinders. Collector size is as important as primary size, and just like with primaries, exhaust moves faster through smaller-diameter collectors. The length of the collector affects the torque curve in the same way as primary length--a longer collector improves low-rpm torque.
Has anyone ever tried the Top Speed Headers? 
