Quote:
Originally Posted by wparsons
Unfortunately, that's not correct on these engines. They only have a single cam profile, it's not like VVTiL in a 2ZZ that has a second cam profile.
As for the reason not all headers behave the same, it all comes down to flow and resonance in the header. If you look at the length of the primaries in the nameless long tube they're quite longer than most of the other headers out there. There's simply no room for a cat in the header with the longer primaries, so you need a cat in over pipe if you need one. Diameters, steps, length between steps, etc all play a part as well.
4-2-1 headers also do better with low end torque than 4-1 headers, but typically at the cost of a little bit of power up top.
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It's not incorrect per se but rather a bad choice of words to decribe what I am guessing they meant. Low speed "profile" and high speed "profile" should have probably read low speed cam "timing" and high speed cam "timing". In layman terms this would essentially result in different flow characteristics at different speeds hence them using the term "profile". I am only going out on a limb here because I dont know who wrote this but it does sound like they may have understood what they meant but just didn't convey it correctly. The headers do smooth the graphs out but the cam timing does in fact have a role in the dip we see as they transition through cam phasing. In your defence I understand how you interpreted what was written to be incorrrect because there are cam systems out there that literally ramp from one side of the lobe to the other that do essentially have different "profiles". When it comes down to it all these parts work in unison and one change affects them all in some way regardless of how small it may be. The alternative header options allow the engine to exhale a little better which translates to a smoothed out area on a graph. If everyone really wants to combat the dip just force feed it with forced induction
